Patent Publication Number: US-2010127848-A1

Title: System, apparatus, method and sensors for monitoring structures

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to civionics and, in particular, to detecting moisture, condensation, leaks, humidity, temperature, pressure and other physical features of structures, such as buildings, and structural materials thereof. 
     2. Description of Related Art 
     Detecting, measuring and monitoring moisture in building materials of buildings provides data and information that can be valuable in the construction, restoration, maintenance and appraisal of such buildings. 
     U.S. Pat. No. 7,142,123 to Kates discloses a method and apparatus for detecting moisture in building materials. Kates discloses a moisture sensor system that includes a plurality of sensor units located throughout a building which communicate with a base unit through a number of repeater units. When a sensor unit detects an anomalous condition, the sensor unit communicates with and provides data regarding the anomalous condition to the base unit directly or through a number of repeater units. At programmed intervals, the sensor unit also “wakes up” and sends status information to the base unit (or repeater) and then listens for commands for a period of time. The sensor units use wireless techniques to communicate with the base unit and/or repeater units. Each repeater includes a first transceiver for communications with a sensor unit and a second transceiver for communications with the base unit. The base unit communicates with a monitoring computer system, which contacts a building manager, maintenance service, alarm service, or other responsible personnel using one or more of several communication systems such as telephone, pager, cellular telephone and/or the Internet and/or a local are network. There may be multiple base units. 
     However, the system of Kates is limited to base units that are unable to perform measurements in the manner of a sensor unit, and is limited to sensor units that are unable to perform functions of a base unit such as communicating by wired communications with the monitoring computer system. 
     Kates also discloses an impedance sensor provided to an impedance probe configured as a pair of conductive strips; an impedance sensor configured to measure impedance using an impedance bridge in which the probe is one leg of the bridge; and an impedance probe configured as a flexible tape, which may have an adhesive and a peel-off layer on the back and/or front of the tape. However, the impedance sensors and impedance probes of Kates are limited in their useability and ease of manufacturing. 
     Canadian patent no. 2,583,006 to Vokey et al. discloses a moisture detection sensor having a first pair of exposed conductors mounted on an insulating substrate for detecting surface moisture and a second pair of penetrated conductors mounted on the insulating substrate to measure moisture content at selected probed locations. A diode guide arrangement allows a monitoring unit to monitor the exposed conductors for surface moisture and the penetrated conductors for moisture content by reversing polarity of the voltage across the conductors. However, the system of Vokey et al. is limited to separating surface moisture measurement from moisture content measurement. 
     SUMMARY 
     The above shortcomings may be addressed by providing, in accordance with one aspect of the invention, a system for monitoring structures. The system includes a measurement acquisition unit having first and second connection points, the measurement acquisition unit being operable to receive at the first connection point a sensor unit electrically connected to the structure, the measurement acquisition unit being operable to receive at the second connection point an electrical connection to the structure, the measurement acquisition unit being operable to electrically isolate the second connection point from the first connection point when invoking the sensor unit so as to produce a measurement result for monitoring the structure. 
     The electrical connection may include a wired communications bus for wired communications with a monitoring center, the measurement acquisition unit being operable to communicate the measurement result to the monitoring center via the wired communications. The measurement acquisition unit may include a third connection point for receiving a distributed power wire, the measurement acquisition unit being operable to electrically isolate the second and third connection points from the first connection point when invoking the sensor unit so as to produce the measurement result. The electrical connection may include a distributed power wire for supplying power to the measurement acquisition unit, the measurement acquisition unit being operable to establish an auxiliary power source for powering the measurement acquisition unit while the measurement acquisition unit is electrically isolated from the distributed power wire. The measurement acquisition unit may be operable to communicate the measurement result via wireless communications, the measurement acquisition unit being operable to select, from among one or more available recipients, a recipient for receiving the measurement result from the measurement acquisition unit, the measurement acquisition unit selecting the recipient such that the number of transmissions required to communicate the measurement result to a monitoring center is minimized. The measurement acquisition unit may be operable to select the recipient so as to maximize signal strength of communications with the recipient if a plurality of the available recipients have associated therewith a same minimal number of transmissions required for communicating the measurement result from the measurement acquisition unit to the monitoring center. The measurement acquisition unit may be operable to set, in response to the measurement result, an amount of time to elapse before producing a subsequent measurement result. The system may include a plurality of the measurement acquisition units, the plurality of the measurement acquisition units comprising a first the measurement acquisition unit wherein the electrical connection comprises a wired communications bus for wired communications with a monitoring center, the plurality comprising a second the measurement acquisition unit being operable to communicate the measurement result via wireless communications to a recipient selected from among available the measurement acquisition units, the second measurement acquisition unit selecting the recipient such that the number of transmissions required to communicate the measurement result to the monitoring center is minimized. The second measurement acquisition unit may be operable to select the recipient so as to maximize signal strength of communications with the recipient if a plurality of the available measurement acquisition units have associated therewith a same minimal number of transmissions required for communicating the measurement result from the second measurement acquisition unit to the monitoring center. The structure may define one or more faces. The first measurement acquisition unit and the second measurement acquisition unit may be located adjacent one of the faces. The first measurement acquisition unit and the second measurement acquisition unit may be aligned for line-of-sight communication therebetween. 
     In accordance with another aspect of the invention, there is provided a system for monitoring a structure. The system includes: (a) measurement acquisition means for producing measurement results, the measurement acquisition means comprising first connection means for receiving a sensor unit electrically connected to the structure, the measurement acquisition means comprising second connection means for receiving an electrical connection to the structure; and (b) isolation means for electrically isolating the second connection means from the first connection means when invoking the sensor unit so as to produce the measurement results. 
     The measurement acquisition means may include wired communication means for communicating the measurement results via wired transmission and comprises wireless communication means for communicating the measurement results via wireless transmission. The measurement acquisition means may include internal powering means for powering the measurement acquisition means when invoking the sensor unit. 
     In accordance with another aspect of the invention, there is provided an apparatus for producing a measurement result to facilitate monitoring a structure. The apparatus includes: (a) a first connector for receiving a sensor unit electrically connected to the structure; (b) a second connector for receiving an electrical connection to the structure; and (c) a switch for electrically isolating the second connector from the first connector when invoking the sensor unit so as to produce the measurement result. 
     The apparatus may include a wired communication transceiver for communicating the measurement result to a monitoring center via wired transmission when a wired communications bus is connected to the second connector. The apparatus may include a third connector for receiving a distributed power wire for supplying power to the apparatus, the switch being operable to electrically isolate the second and third connectors from the first connector when invoking the sensor unit so as to produce the measurement result. The electrical connection may include a distributed power wire for supplying power to the apparatus, the apparatus further comprising an auxiliary power source for powering the apparatus when the switch is electrically isolating the second connector from the first connector. The auxiliary power source may include a capacitor. The apparatus may include a wireless communication transceiver for communicating the measurement result via wireless transmission. The apparatus may include a sensor circuit operable to selectively invoke a reference resistance, the apparatus being operable to receive a measurement sensor having a pair of spaced apart conductors and an impedance circuit electrically connected in parallel with the pair of conductors, the impedance circuit having a finite impedance. 
     In accordance with another aspect of the invention, there is provided a method of monitoring a structure. The method involves: (a) receiving at a first connector of a measurement acquisition unit a sensor unit electrically connected to the structure; and (b) invoking the sensor unit so as to produce a measurement result for monitoring the structure, wherein invoking the sensor unit so as to produce a measurement result for monitoring the structure comprises electrically isolating a second connector of the measurement acquisition unit from the first connector. 
     The method may involve receiving at the second connector a wired communications bus for communicating the measurement result to a monitoring center via wired transmission. The method may involve receiving at a third connector of the measurement acquisition unit a distributed power wire for supplying power to the measurement acquisition unit, and wherein electrically isolating a second connector of the measurement acquisition unit from the first connector when invoking the sensor unit comprises electrically isolating the second and third connectors from the first connector when invoking the sensor unit. The method may involve receiving at the second connector a distributed power wire for supplying power to the measurement acquisition unit, and wherein electrically isolating a second connector of the measurement acquisition unit from the first connector when invoking the sensor unit comprises establishing an auxiliary power source for powering the measurement acquisition unit. Establishing an auxiliary power source for powering the measurement acquisition unit may involve charging a capacitor by power received from the distributed power wire. The method may involve: (a) determining a number of available recipients operable to receive the measurement result from the measurement acquisition unit via wireless communication; (b) if there are one or more the available recipients, selecting a recipient from among the one or more available recipients; and (c) if there are no the available recipients, storing in a memory of the measurement acquisition unit the measurement result and a measurement count in association therewith. If there are one or more the available recipients, selecting a recipient from among the one or more available recipients may involve selecting the recipient such that the number of transmissions required to communicate the measurement result from the measurement acquisition unit to a monitoring center is minimized. Selecting the recipient such that the number of transmissions required to communicate the measurement result to a monitoring center is minimized may involve, if a plurality of the available recipients have associated therewith a same minimal number of transmissions required to communicate the measurement result from the measurement acquisition unit to the monitoring center, selecting the recipient such that signal strength of communications between the recipient and the measurement acquisition unit is maximized. The method may involve transmitting by the measurement acquisition unit to the recipient via wireless communication the measurement result and any previously stored measurement results and associated measurement counts not previously transmitted by the measurement acquisition unit. The method may involve receiving by a second measurement acquisition unit the measurement result, and transmitting by the second measurement acquisition to a monitoring center via wired communication the measurement result. The method may involve setting, in response to the measurement result, an amount of time to elapse before producing a subsequent measurement result. 
     In accordance with another aspect of the invention, there is provided a measurement sensor for detecting moisture. The measurement sensor includes: (a) a pair of spaced apart conductors; and (b) an impedance circuit electrically connectable in parallel with the pair of conductors and having a finite impedance such that when the impedance circuit is connected an impedance of the measurement sensor greater than the finite impedance indicates an impaired connection. 
     The impedance circuit may connected to the pair of conductors proximate to a connection end of the measurement sensor. The impedance circuit may be connected to the pair of conductors proximate to a terminal end of the measurement sensor. The impedance circuit may include a thermistor such that the impedance of the impedance circuit varies with temperature. The impedance circuit may include a diode such that the impedance of the impedance circuit varies with the polarity of a voltage applied to the measurement sensor. The impedance circuit may include at least one sub-circuit electrically connectable in parallel with the pair of conductors, the at least one sub-circuit comprising at least one diode in series with at least one other electrical component. The at least one sub-circuit may include first and second sub-circuits, the first sub-circuit comprising a first diode disposed in a first direction, the second sub-circuit comprising a second diode disposed in a second direction opposite the first direction. The measurement sensor may include a non-hydrophobic material attached to the pair of spaced conductors. The measurement sensor may have a first diode connected to the pair of conductors in a first direction at a connection end of the pair of conductors. The measurement sensor may include a second pair of spaced apart conductors. The measurement sensor may include a second diode connected to the second pair of conductors in a second direction at a second connection end of the second pair of connectors. The measurement sensor may include a second impedance circuit connected to the second pair of conductors proximate to a second terminal end of the second pair of conductors. The second impedance circuit having a second finite impedance such that an impedance of the measurement sensor that is determined in accordance with the second direction to be greater than the second finite impedance indicates an impaired connection. 
     In accordance with another aspect of the invention, there is provided a termination module for a moisture detection measurement sensor, the sensor comprising a pair of spaced apart conductors. The termination module includes: (a) a base attachable to the sensor; and (b) an impedance circuit supported by the base such that the impedance circuit is electrically connected in parallel with the pair of conductors when the base is attached to the sensor, the impedance circuit having a finite impedance such that when the base is attached to the sensor an impedance of the measurement sensor greater than the finite impedance indicates an impaired connection. 
     The base may include a printed circuit board dimensioned to receive a pair of probes, the impedance circuit being electrically connected between the pair of probes when the pair of probes is being received by the printed circuit board. The termination module may include a temperature sensor supported by the base. The impedance circuit may include a diode such that the impedance of the impedance circuit varies with the polarity of a voltage applied to the impedance circuit. The impedance circuit may include first and second sub-circuits, the first sub-circuit comprising a first diode disposed in a first direction in series with at least one other electrical component, the second sub-circuit comprising a second diode disposed in a second direction opposite the first direction. 
     In accordance with another aspect of the invention, there is provided a moisture content measurement sensor for measuring moisture content of a structural material. The moisture content measurement sensor includes: (a) a pair of spaced apart conductors enclosed within an electrically insulating material; and (b) a plurality of electrically conductive probe supports, each of the probe supports being attached to one of the conductors and dimensioned to receive a probe for insertion into the structural material, each of the probe supports forming an electrical connection between the one conductor and the probe. 
     Each of the probe supports may include an eyelet rivet. The moisture content measurement sensor may include an impedance circuit electrically connectable in parallel with the pair of conductors and having a finite impedance such that when the impedance circuit is connected an impedance of the measurement sensor greater than the finite impedance indicates an impaired connection. The plurality of electrically conductive probe supports may include at least one pair of the probe supports, the at least one pair being dimensioned to receive a termination module comprising a base and an impedance circuit supported by the base such that the impedance circuit is electrically connected in parallel with the at least one pair when the termination module is received by the at least one pair, the impedance circuit having a finite impedance such that when the termination module is received by the at least one pair an impedance of the moisture content measurement sensor greater than the finite impedance of the impedance circuit alone indicates an impaired connection. 
     In accordance with another aspect of the invention, there is provided a measurement sensor for monitoring a structure. The measurement sensor includes: (a) measurement sensing means for measuring a feature of the structure; and (b) connection test means for indicating an impaired connection of the measurement sensor, the connection test means being electrically connectable in parallel with the measurement sensing means and having a finite impedance such that when said connection test means is connected an impedance of the measurement sensor greater than the finite impedance indicates the impaired connection. 
     Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of embodiments of the invention in conjunction with the accompanying figures and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In drawings which illustrate by way of example only embodiments of the invention: 
         FIG. 1  is a perspective view of a building installation of a system for monitoring a structure according to a first embodiment of the invention; 
         FIG. 2  is a block diagram of a data acquisition unit of the system shown in  FIG. 1 , showing a sensor circuit controlled by a processor; 
         FIG. 3  is a schematic representation of sensor circuitry of the data acquisition unit shown in  FIG. 2 , showing first and second reference resistors; 
         FIG. 4  is a flow diagram of a method of the system shown in  FIG. 1  of monitoring a structure in accordance with the first embodiment of the invention; 
         FIG. 5  is a flow diagram of an exemplary method of performing the step shown in  FIG. 4  of determining an operating mode of the data acquisition unit shown in  FIG. 2 ; 
         FIG. 6  is a flow diagram of an exemplary method of performing the step shown in  FIG. 4  of providing a measurement result in accordance with the operating mode; 
         FIG. 7  is a flow diagram of an exemplary method of performing the step shown in  FIG. 6  of producing the measurement result in wired mode, showing the step of electrically isolating from a bus; 
         FIG. 8  is a flow diagram of an exemplary method of performing the step shown in  FIG. 6  of updating a profile of the data acquisition unit shown in  FIG. 2 ; 
         FIG. 9  is a flow diagram of an exemplary method of performing the step shown in  FIG. 6  of producing the measurement result in wireless mode, showing the step of electrically isolating from a power conduit; 
         FIG. 10  is a flow diagram of an exemplary method of performing the step shown in  FIG. 6  of transmitting the measurement result to a preferred recipient, showing steps for selecting the preferred recipient; 
         FIG. 11  is a flow diagram of an exemplary method of performing the step shown in  FIG. 6  of setting a power state of the data acquisition unit shown in  FIG. 2 , showing reconfiguring pins for low leakage; 
         FIG. 12  is a flow diagram of a method of the system shown in  FIG. 1  of responding to a communication received from the data acquisition unit shown in  FIG. 2 ; 
         FIG. 13  is a top view of a prior art leak detection tape, showing a pair of spaced apart conductors and a substrate; 
         FIG. 14  is a sectional view along lines  14 - 14  of the prior art leak detection tape shown in  FIG. 13 , showing an adhesive layer; 
         FIG. 15  is an end view of an encloseable moisture content sensor suitable for use with the system shown in  FIG. 1 , showing two spaced apart adhesive layers; 
         FIG. 16  is a top view of a moisture content sensor suitable for use with the system shown in  FIG. 1 , showing an enclosure made of an electrically insulating material; 
         FIG. 17  is a sectional view along lines  17 - 17  of the moisture content sensor shown in  FIG. 16 , showing an eyelet rivet in cross-section; 
         FIG. 18   a  is a top view of a measurement sensor suitable for use with the system shown in  FIG. 1 , showing a schematic representation of an impedance circuit comprising a reference impedance; 
         FIG. 18   b  is a top view of the measurement sensor shown in  FIG. 18   a , showing a schematic representation of the impedance circuit comprising a thermistor; 
         FIG. 18   c  is a top view of the measurement sensor shown in  FIG. 18   a , showing a schematic representation of the impedance circuit comprising a diode; 
         FIG. 18   d  is a top view of the measurement sensor shown in  FIG. 18   a , showing a schematic representation of the impedance circuit comprising a dual reference impedance circuit; 
         FIG. 18   e  is a top view of the measurement sensor shown in  FIG. 18   a , showing two pairs of conductors and a diode arrangement for selection therebetween; 
         FIG. 19   a  is a top view of a termination module suitable for use with the system shown in  FIG. 1 , showing a printed circuit board (PCB); 
         FIG. 19   b  is a top view of the termination module shown in  FIG. 19   a , showing the termination module attached to a leak detection and moisture content measurement sensor at its termination end; 
         FIG. 20   a  is a top view of a variation of the termination module shown in  FIG. 19   a , showing a cable housing; and 
         FIG. 20   b  is a top view of the termination module shown in  FIG. 20   a , showing the termination module attached to a condensation sensor at its connection end. 
     
    
    
     DETAILED DESCRIPTION 
     A system for monitoring a structure includes: (a) measurement acquisition means for producing measurement results, the measurement acquisition means including first connection means for receiving a sensor unit electrically connected to the structure, the measurement acquisition means including second connection means for receiving an electrical connection to the structure; and (b) isolation means for electrically isolating the second connection means from the first connection means when invoking the sensor unit so as to produce the measurement results. The measurement acquisition means may include wired communication means for communicating the measurement results via wired transmission. The measurement acquisition means may include wireless communication means for communicating the measurement results via wireless transmission. The measurement acquisition means may include internal powering means for powering the measurement acquisition means when invoking the sensor unit. 
     Referring to  FIG. 1 , the system according to a first and preferred embodiment of the invention is shown generally at  10 . The system  10  is operable to monitor a structure such as the building  12  shown in  FIG. 1 . The system is operable to monitor the building  12  by measuring moisture, condensation, leaks, humidity, temperature, heat flux, pressure, air quality, presence of gases, presence of volatile chemicals, and other physical features of the building  12 . The terms measure, measurement and grammatical variations thereof are used herein to refer to any form of sensing, quantifying, representing or detecting any physical phenomena related to any form of structure, structural material or the environment of or within a structure or structural material. 
     The building  12  may have any structural size and shape with one or more faces such as the walls  14  shown in  FIG. 1 . While  FIG. 1  shows the building  12  having the exemplary vertically planar exterior walls  14 , the faces of the building  12  may have any contour and have any slope at any point thereof. A face of a structure may be a sloped and curved rooftop and/or roof membrane (not shown), for example. 
     The system  10  includes any number of measurement acquisition units such as the data acquisition units  16  mounted on, installed in or otherwise located in proximity to the building  12 . Each data acquisition unit  16  is operable to cause measurements for monitoring the building  12  to be performed. Preferably, at least one data acquisition unit  16  is operable to provide measurement results of such measurements to a monitoring center such as the gateway  18  shown in  FIG. 1 . The system  10  may include any number of gateways  18 . Each gateway  18  is typically mounted on or installed in the building  12 . However, any given gateway  18  may be mounted or installed at any location within wired or wireless communication range of one or more data acquisition units  16 . 
     The gateway  18  may, for example, be any computing device such as a general purpose computer, microcomputer, minicomputer, mainframe computer, distributed network for computing, functionally equivalent discrete hardware components, etc. and any combination thereof. 
     In the first embodiment, the gateway  18  can receive data, such as digital data representing a measurement result, from at least one of the data acquisition units  16 . As shown in  FIG. 1 , the data may be received by wired communication, wireless communication or any combination thereof by any communication network arrangement between the gateway  18  and the data acquisition units  16 . 
     The gateway  18  in at least some embodiments can process data received from a data acquisition unit for monitoring the building  12 . Such data processing might include for example communicating the data to a central monitoring center (not shown) by any industry standard or proprietary communications technique including by Internet or other network connection (not shown); uploading data for inclusion in a webpage of a website; storing data in a database (not shown) for later retrieval; data analysis such as to produce monitoring status, statistics or information related to the building  12 ; triggering an event such as an alarm event in response to the received data; communicating an event to personnel or a processor by e-mail, SMS (Short Message Service) message, pager message, graphic display, visual indicator, audible indicator, tactile indicator such as a vibration, initiation of a mechanical force such as activation of an electromechanical relay, and any combination thereof; communicating event-related information to one or more data acquisition units  16 , such as communicating an alarm to a data acquisition unit  16  in response to data received from that data acquisition unit  16 ; activating an actuator such as by relay activation; and any combination thereof. 
     The gateway  18  in the first embodiment is operable to communicate with at least one data acquisition unit  16  by a wired connection such as the CAN (Control Area Network) bus  20  shown in  FIG. 1 . In the exemplary embodiment shown in  FIG. 1 , the CAN bus  20  extends between the gateway  18  and eight data acquisition units  16  located along the periphery of the top of the building  12 . In general, the CAN bus  20  may include any number of separate or connected wired connections and may form or include a star, tree, cluster, ring or any other wired network arrangement, for example. In the system  10 , at least one data acquisition unit  16  is preferably operable to communicate directly with the gateway  18 , which in the first embodiment includes communicating directly with the gateway  18  via the CAN bus  20 . 
     Communication between data acquisition units  16  may occur by any suitable technique, including by wireless and/or wired communication. In the exemplary embodiment shown in  FIG. 1 , twelve data acquisition units  16  not directly connected to the CAN bus  20  are visible, including eleven data acquisition units  16  located adjacent an exterior wall  14  and one data acquisition unit  16  located within the interior of the building  12  and made visible by the cut-out of  FIG. 1 . In the first embodiment, each data acquisition unit  16  is operable to communicate with a specifiable other data acquisition unit  16  by wireless communications. In the exemplary embodiment shown in  FIG. 1 , the wired and wireless data acquisition units  16  form a wired/wireless hybrid network with a tree cluster type network arrangement. Along a given wall  14 , a number of data acquisition units  16  not connected to the CAN bus  20  are operable to cause measurements to be performed and to communicate measurement results by wireless communications to a data acquisition unit  16  connected to the CAN bus  20  and located near the top of the given wall  14 . The data acquisition unit  16  connected to the CAN bus  20  is then operable to transmit measurement results received from other data acquisition units  16  to the gateway  20  via wired communications along the CAN bus  20 . Furthermore, any number of data acquisition units  16  may be located within the interior of the building  12  and operable to communicate measurement results to a data acquisition unit  16  located at the exterior of the building  12  such as for retransmission to a data acquisition unit  16  connected to the CAN bus  20 . 
     The number of transmissions required to deliver a communication from a given data acquisition unit  16  to a data acquisition unit  16  in wired communication with the gateway  18  may be referred to as the hop count for that given data acquisition unit  16 . For example, the data acquisition units  16  connected to the CAN bus  20  each have hop counts of zero. Data acquisition units have a hop count of one if operable to communicate with a CAN bus  20  connected data acquisition unit  16 . Other hop count values are possible. 
     Locating at least one data acquisition unit  16  at a given wall  14  for receiving measurement results from a number of other data acquisition units  16  also located at the given wall  14  advantageously permits line-of-sight wireless communication between the at least one data acquisition unit  16  and the other data acquisition units  16 . As shown in the exemplary embodiment of  FIG. 1 , the wall  14  has a generally flat exterior surface, thereby permitting visual line-of-sight communication between the at least one data acquisition unit  16  and the the other data acquisition units  16 . However, in general the wall  14  may have any contour, and the line-of-sight wireless communication need not be limited to visual line-of-sight communication. The system  10  is operable to advantageously make use of the wall  14 , having any countour, as a ground plane for wireless communications, thereby improving the signal-to-noise ratio of such communications. 
     Any communication between data acquisition units  16 , between a data acquisition unit  16  and the gateway  18 , and/or with the central monitoring center (not shown) may be transmitted in accordance with any communications protocol, including employing encryption or other techniques for enhancing security of communications. Any communication of the system  10  may involve transmission at any frequency, frequencies or ranges thereof, including using an available 900 MHz and/or 2.4 GHz frequency band. 
     Referring to  FIG. 2 , the data acquisition unit  16  in the first embodiment includes a processing circuit, such as the processor  22 , and a memory circuit such as the memory  24 . 
     The processor  22  is typically a processing circuit that includes one or more circuit units, such as a central processing unit (CPU), digital signal processor (DSP), embedded processor, etc., and any combination thereof operating independently or in parallel, including possibly operating redundantly. The processor  22  may be implemented by one or more integrated circuits (IC), including being implemented by a monolithic integrated circuit (MIC), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), etc. or any combination thereof. Additionally or alternatively, the processor  22  may be implemented as a programmable logic controller (PLC), for example. The processor  22  may include circuitry for storing memory, such as digital data, and may comprise the memory  24  or be in wired communication with the memory  24 , for example. In the first embodiment, the processor  22  includes, or is otherwise in communication with, timing circuitry for implementing a timer. 
     The memory  24  in the first embodiment is operable to store digital representations of data or other information, including measurement results, and to store digital representations of program data or other information, including program code for directing operations of the processor  22 . 
     Typically, the memory  24  is all or part of a digital electronic integrated circuit or formed from a plurality of digital electronic integrated circuits. The memory  24  may be implemented as Read-Only Memory (ROM), Programmable Read-Only Memory (PROM), Erasable Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM), flash memory, one or more flash drives, universal serial bus (USB) connected memory units, magnetic storage, optical storage, magneto-optical storage, etc. or any combination thereof, for example. The memory  24  may be operable to store digital representations as volatile memory, non-volatile memory, dynamic memory, etc. or any combination thereof. 
     In at least some embodiments, the data acquisition unit  16  includes an internal temperature sensor  26  for sensing the temperature at the data acquisition unit  16 . In such embodiments, the data acquisition unit  16  can invoke the internal temperature sensor  26  so as to produce the internal temperature of the data acquisition unit  16 , and can communicate that temperature to the gateway  18  as an indication of an ambient temperature of the building  12  at the location of that data acquisition unit  16 . 
     In at least some embodiments, the data acquisition unit  16  includes an internal pressure sensor  28  for sensing pressure, such as differential pressure at terminal ends of a pair of pressure tubes (not shown) connected externally to the data acquisition unit  16  at the pressure tube connectors  30 . In such embodiments, the data acquisition unit  16  can invoke the internal pressure sensor  28  so as to produce a differential pressure measurement result to facilitate monitoring the building  12 . 
     In the first embodiment, the data acquisition unit  16  includes a plurality of measurement sensor connectors  32  for connecting to external measurement sensor units (not shown in  FIG. 2 ). Such measurement sensor units may be of any type and function to perform measurements of any kind, including for example sensing, quantifying, detecting or otherwise measuring moisture, condensation, leaks, humidity, temperature, heat flux, pressure, air quality, presence of gases, presence of volatile chemicals, and other physical features of, within or surrounding structures or structural materials thereof. 
     In the exemplary embodiment of  FIG. 2 , two measurement sensor connectors  32  are shown connected to an interface circuit  34 , and one of the exemplary interface circuits includes a power supply voltage connection  36 . In general, each measurement sensor connector  32  may be connected to interface circuits  34  that are identical, or different measurement sensor connectors  32  may be connected to different interface circuits  34  for optimal use with different measurement sensor units (not shown in  FIG. 2 ) or different types of measurement sensor units. Each interface circuit  34  may include electronic conditioning circuitry for interfacing with one or more measurement sensor units or one or more types of measurement sensor units. 
     Whether through an interface circuit  34  or not, in various embodiments the measurement sensor connectors  32  are connected to a measurement sensor selector such as the measurement sensor switch  38  for separately connecting one measurement sensor connector  32  to an electronic circuit such as the sensor circuit  40  shown in  FIG. 2 . The sensor circuit  40  can be any electronic circuit connected between the measurement sensor switch  38  and the processor  22 . 
     In the first embodiment, the sensor circuit  40  includes sensor driver circuitry for receiving a measurement result produced by a measurement sensor unit connected externally to a given measurement sensor connector  32 . The interface circuit  34 , the sensor circuit  40 , both or neither may include in various embodiments analog conditioning circuitry such as circuitry for amplification, including automatic gain control amplification and/or gain range selectable amplification, buffering, circuitry for filtering, including low-pass filtering to reduce noise, or other suitable electronic circuitry. 
     In the first embodiment, the sensor circuit  40  includes an analog-to-digital converter for converting analog measurement results, obtained by invoking the measurement sensor unit, to digital measurement results, which can be readily received as input by the processor  22 . In some embodiments, the data acquisition unit  16  includes a plurality of analog-to-digital converters, including having different analog-to-digital converters operable to perform analog-to-digital conversion at different precision levels. The data acquisition unit  16  may include one high-precision analog-to-digital converter and one standard- or low-precision analog-to-digital converter, for example. The sensor circuit  40  need not include a power supply voltage connection  36  in all embodiments. Power provided via the power supply voltage connection  36  may be of any suitable type, including being provided by a low drift voltage reference output. 
     The interface circuit  34 , the measurement sensor switch  38  and the sensor circuit  40  may each be implemented by electronic circuitry internal to the processor  22 , external to the processor  22 , or any combination thereof. While for simplicity of illustration  FIG. 2  shows one set of measurement sensor connectors  32 , two interface circuits  34 , one measurement sensor switch  38  and one sensor circuit  40 , the data acquisition unit  16  may include any number of sets of measurement sensor connectors  32 , any number of interface circuits  34 , any number of measurement sensor switches  38 , any number of sensor circuits  40 , and any combination thereof including bypassing the measurement sensor switch  38  in respect of one or more measurement sensor connectors  32  for example. 
     Referring to  FIG. 3 , exemplary circuitry for implementing the sensor circuit  40  in accordance with some embodiments is shown generally at  42 . The sensor circuitry  42  includes one power supply voltage connection  36 , which is connected to one switching portion  44  of the measurement sensor switch  38  operable to connect and disconnect the one measurement sensor connector  32  shown in  FIG. 3 . When the switching portion  44  is closed, such as by being closed under the control of the processor  22 , electrical power, provided by the power supply voltage connection  36 , is connected to one terminal  46  of the switching portion  44  so as to apply a voltage to any measurement sensor unit (not shown in  FIG. 3 ) connected externally to the measurement sensor connector  32 . The other terminal  48  of the measurement sensor connector  32  is also connected to the switching portion  44 . When the switching portion  44  is closed, the other terminal  48  connects to the sensor circuitry  42  such that the sensor circuitry  42  is operable to receive a measurement result produced by the connected measurement sensor unit. The switching portion  44  preferably provides a low loss connection between the measurement sensor unit and the sensor circuitry  42 . 
     For receiving measurement results, the sensor circuitry  42  includes a reference resistor  50  connected between the switching portion  44  output and an analog ground  52  of the sensor circuitry  42 , as shown in  FIG. 3 . The reference resistor  50  may be a high precision reference resistor having a resistance value of typically 1 Mega-ohms and a resistance precision of 1%, 0.1% or 0.01% for example. In some embodiments including that shown in  FIG. 3 , a shunt capacitor  54 , connected in parallel with the reference resistor  50 , advantageously reduces high frequency noise so as to enhance measurement accuracy of the data acquisition unit  16 . In some embodiments, the shunt capacitor  54  has a capacitance value of up to 50 nF, including having a capacitance value of 470 pF. However, the shunt capacitor  54  need not be used in all embodiments and may be omitted from at least some embodiments. The sensor circuitry  42  also includes a second reference resistor  56  connected in series with a reference switch  58 . The second reference resistor  56  typically has a lower resistance value than the reference resistor  50 , such as a resistance value of 100 kohms for example. The second reference resistor  56  may have any resistance precision including 1%, 0.1% and 0.01% for example. The reference switch  58  is typically under the control of the processor  22  and can connect and disconnect the second reference resistor  56  between the switching portion  44  output and the analog ground  52 . The reference switch  58  advantageously permits the data acquisition unit  16  to select the shunt resistance between the switching portion  44  output and the analog ground  52 . Closing the reference switch  58  advantageously decreases a settling time of the measurement circuitry after closing the switching portion  44 . In some embodiments, the processor  22  is operable to close the switching portion  44  and the reference switch  58 , wait the reduced settling time, open the reference switch  58  and proceed with receiving a measurement result using the voltage divider created by the measurement sensor unit and the reference resistor  50 . In some embodiments, the processor  22  also waits a second settling time after the reference switch has been opened and before receiving the measurement result. Additionally or alternatively, the processor  22  may be operable to receive a measurement result while both the switching portion  44  and the reference switch  58  are closed. As shown in  FIG. 3 , the sensor circuitry  42  includes a buffer amplifier  60 , which preferably has a low leakage current high impedance input for improved measurement accuracy. The buffer amplifier  60  output connects to the input of an analog-to-digital converter  62  for converting the analog measurement result received by the sensor circuitry  42  to digital representations thereof. In some embodiments, the output of the analog-to-digital converter  62  is connected to an input of the processor  22 . Additionally or alternatively, the buffer amplifier  60 , the analog-to-digital converter  62 , or both the buffer amplifier  60  and the analog-to-digital converter  62  may form part of the processor  22 . 
     Referring back to  FIG. 2 , an output of the processor  22  is connected to an input of the sensor circuit  40 , and an output of the sensor circuit  40  is connected to an input of the processor  22 . The processor  22  can invoke a measurement sensor unit through the sensor circuit  40  or portion thereof, measurement sensor switch  38 , any interface circuit  34  present and a selected measurement sensor connector  32  to produce a measurement result received by the processor  22  from the selected measurement sensor connector  32  via any one or more of the interface circuit  34 , the measurement sensor switch  38  and the sensor circuit  40 . 
     In the first embodiment shown in  FIG. 2 , the processor  22  is operable to store received measurement results in the memory  24 , including storing on a temporary basis as volatile memory data and/or storing for long term data storage as non-volatile memory data. 
     In the first embodiment shown in  FIG. 2 , the data acquisition unit  16  includes a measurement result selector, such as the measurement result switch  64  shown in  FIG. 2 , connected to receive a measurement result output of the processor  22 . In the first embodiment, the measurement result switch  64  is operable to provide such measurement result to a wireless transceiver  66  having a transceiver antenna  68  for communicating the measurement result via wireless transmission, to a bus transceiver  70  for communicating the measurement result via wired transmission, or to neither the wireless transceiver  66  nor the bus transceiver  70  in which case a remainder section of the data acquisition unit  16 , including the processor  22  and the measurement sensing circuitry of the data acquisition unit  16 , are electrically isolated from the bus transceiver  70 . Typically, the measurement result switch  64  is under the control of the processor  22 , which directs the measurement result switch  64  to select a specified output of the measurement result switch  64  for a specifiable duration, including possibly until further directed to change its selection. While the measurement result switch  64  is shown in  FIG. 2  as having three selectable outputs, in some embodiments only two selectable outputs are used to permit a selection between the wireless transceiver  66  and the bus transceiver  70  such that when the wireless transceiver  66  is selected the remainder section of the data acquisition unit  16  is electrically isolated from the bus transceiver  70 . 
     The wireless transceiver  66  in the first embodiment is operable to communicate via wireless transmission with other devices capable of wireless communications. Such other devices may include another data acquisition unit  16 , the gateway  18 , any device operable to communicate by wireless transmission in accordance with a wireless communication protocol that is compatible with that of the wireless transceiver  66 , and any other suitable device for example. The system  10  is operable in various embodiments to effect communications by any suitable wireless connection, including a radio link, a cellular telephone link, a satellite link, a line-of-sight link, including a line-of-sight radio link and/or a line-of-sight free optical link, and any combination thereof for example. 
     In at least some embodiments, the transceiver antenna  68  is advantageously directional such that line-of-sight wireless communication between data acquisition units adjacent a given wall  14  ( FIG. 1 ) can be facilitated by directing the respective transceiver antennas  68  accordingly. For example, a data acquisition unit  16  connected to the CAN bus  20  and located near the top of a given wall  14  ( FIG. 1 ) may have its transceiver antenna  68  directed in a generally downward direction along the given wall  14  for receiving communications from other data acquisition units  16  located at the given wall  14 , while such other data acquisition units  16  may have their respective transceiver antennas  68  directed in a generally upward or otherwise toward the data acquisition unit  16  connected to the CAN bus  20 . A person of ordinary skill in the art will appreciate that an innumerable variety of arrangements forming a variety of network architectures, including a cluster tree type network architecture, are possible. The illustrated arrangement of  FIG. 1  is exemplary only. 
     The bus transceiver  70  in the first embodiment of  FIG. 2  is operable to communicate by wired transmission with other devices capable of wired communications. Such other devices may include the gateway  18 , another data acquisition unit  16 , any device operable to communicate by wired transmission in accordance with a wired communication protocol that is compatible with that of the bus transceiver  70 , and any other suitable device for example. The system  10  is operable in various embodiments to effect communications by any suitable wired connection, including a copper wire link, a coaxial cable link, stripline or other printed circuit trace link, a waveguide link, a fiber-optic transmission link, and any combination thereof for example. 
     As shown in  FIG. 2 , the bus transceiver  70  is connected at its output to a bus switch  72 , which is connected between the bus transceiver  70  and a bus connector  74 . The bus switch  72  can disconnect and electrically isolate the bus connector  74  from the remainder of the data acquisition unit  16  including the bus transceiver  70 . Typically, the operation of the bus switch  72  is under the control of the processor  22  such that the bus switch  72  opens and closes in response to commands produced by the processor  22 . 
     The bus connector  74  in the first embodiment is dimensioned to receive a wired communications bus such as the CAN bus  20  ( FIG. 1 ). Additionally or alternatively, the bus connector  74  may be compatible with other physical wired communications buses (not shown). 
     For comprehensive exemplary illustration, both the measurement result switch  64  and the bus switch  72  are shown in  FIG. 2  as being operable to electrically disconnect the bus connector  74  from other parts of the data acquisition unit  16 . However, it is not necessary for all embodiments to include both such operabilities and, in various embodiments, the bus switch  72  or the ability of the measurement result switch  64  to electrically isolate the remainder section of the data acquisition unit  16  from the bus transceiver  70  is omitted. 
     In accordance with the first embodiment shown in  FIG. 2 , the data acquisition unit  16  is operable to function in a distributed power mode in which the data acquisition unit  16  is powered via a connection to an external power source and/or a stand-alone power mode in which the data acquisition unit  16  is self-powered by a stand-alone power source. 
     As shown in  FIG. 2 , the first embodiment includes a distributed power connector  76  for receiving power from an external power source (not shown) such as a distributed power source (not shown). Such distributed power source may be operable to provide power to any number of data acquisition units  16 , for example, and may be of any power supply type. The distributed power connector  76  is preferably dimensioned for receiving a power conduit (not shown) suitable for providing electrical power of the external power source. The data acquisition unit  16  is in some embodiments operable to receive DC (Direct Current) power, typically at a substantially constant voltage such as +5 volts, via the distributed power connector  76 . Additionally or alternatively, the data acquisition unit  16  may be operable to receive AC (Alternating Current) power, typically at a substantially constant alternating frequency and within a specifiable voltage range, via the distributed power connector  76 . In at least some embodiments where AC power is received, the data acquisition unit  16  includes power supply circuitry operable to convert the AC power to DC power for use by components of the data acquisition unit  16 . 
     In the first embodiment, the data acquisition unit  16  includes a stand-alone power connector, such as the battery connector  78 , for receiving power from a stand-alone power source such as a battery (not shown) for supplying power to the data acquisition unit  16 . Typically, the battery connector  78  permits the data acquisition unit  16  to receive DC power. In various embodiments, the battery connector  78  is not limited to receiving power from a battery, but may be dimensioned for receiving power from any suitable type of stand-alone power source, including a stand-alone electrical generator, solar panel unit, wind turbine unit, or any combination thereof for example. In some embodiments, the data acquisition unit  16  is operable to be powered by vibration sensing means and/or by induced voltages. 
     The data acquisition unit  16  in the first embodiment includes a selector, such as the power mode switch  80 , for selecting between receiving power through the distributed power connector  76 , receiving power through the battery connector  78 , and neither receiving power through the distributed power connector  76  nor through the battery connector  78  such that a remaining portion of the data acquisition unit  16  is electrically isolated from the distributed power connector  76 . While the power mode switch  80  is shown in  FIG. 2  as having three selectable outputs, in some embodiments only two selectable outputs are used to permit a selection between the distributed power connector  76  and the battery connector  78  such that when the battery connector  78  is selected the remaining portion of the data acquisition unit  16  is electrically isolated from the distributed power connector  76 . 
     The first embodiment preferably includes an auxiliary power source, such as the super capacitor  82  shown in  FIG. 2 , for powering the data acquisition unit  16  while the remaining portion of the data acquisition unit  16  is electrically isolated from the distributed power connector  76  and/or the battery connector  78 . While the exemplary embodiment of  FIG. 2  shows the auxiliary power source implemented as a super capacitor  82 , any power source electrically isolated from the building  12  may suitably be employed, including any capacitor, battery, electrical generator, renewable energy source such as a solar panel unit or wind turbine unit, etc., and any combination thereof for example. 
     The auxiliary power switch  84  of the first embodiment is operable to connect, and disconnect, the super capacitor  82  to, and from, other components of the data acquisition unit  16 . The data acquisition unit  16  is advantageously operable in the first embodiment to select between receiving power from the super capacitor  82 , through the distributed power connector  76  or through the battery connector  78 . The data acquisition unit  16  is furthermore operable in the first embodiment to form a connection between the super capacitor  82  and power received either through the distributed power connector  76  or the battery connector  78 , thereby permitting the super capacitor  82  to be charged up. The super capacitor  82  is operable to discharge by supplying power to the data acquisition unit  16 , for example. 
     As is well known in the art, at least some measurement sensor units include electrical connections to a structure being sensed by the measurement sensor unit. For example, such measurement sensor units may include probes inserted into the structure or a material thereof. By way of further example, structural fasteners inserted into the structure during construction, maintenance, renovation or repair of the structure may be inadvertently inserted through at least a portion of a measurement sensor unit, thereby creating an electrical connection to the structure. 
     The data acquisition unit  16  in the first embodiment is advantageously operable to invoke a given measurement sensor unit while being electrically connected to the building  12  only through that measurement sensor unit. In the first embodiment, accomplishing such single electrical connection to the building  12  involves electrically isolating portions of the data acquisition unit  16 , including the processor  22  and the measurement sensor connection  32  connected to the given measurement sensor unit, from one or more of the bus connector  74 , bus transceiver  70 , wireless transceiver  66 , distributed power connector  76  and the battery connector  78 . Such electrical isolation advantageously avoids electrical ground loops, which might otherwise adversely affect the accuracy and/or precision of measurement results produced by the system  10 . Such electrical isolation advantageously permits the system  10  to permit measurements to be performed simultaneously by multiple data acquisition units  16 , including multiple data acquisition units  16  installed at the same building  12 , thereby enhancing efficiencies in producing measurement results. 
     Thus, there is provided a system for monitoring a structure, the system comprising a measurement acquisition unit having first and second connection points, said measurement acquisition unit being operable to receive at said first connection point a sensor unit electrically connected to the structure, said measurement acquisition unit being operable to receive at said second connection point an electrical connection to the structure, said measurement acquisition unit being operable to electrically isolate said second connection point from said first connection point when invoking said sensor unit so as to produce a measurement result for monitoring the structure. 
     In accordance with another aspect of the invention, there is thus provided an apparatus for producing a measurement result to facilitate monitoring a structure, the apparatus comprising: (a) a first connector for receiving a sensor unit electrically connected to the structure; (b) a second connector for receiving an electrical connection to the structure; and (c) a switch for electrically isolating said second connector from said first connector when invoking said sensor unit so as to produce the measurement result. 
     Method of Operation 
     Referring to  FIG. 2 , the memory  24  of a given data acquisition unit  16  in accordance with the first embodiment of the invention contains blocks of code comprising computer executable instructions for directing the processor  22 . Additionally or alternatively, such blocks of code may form part of a computer program product comprising computer executable instructions embodied in a signal bearing medium, which may be a recordable computer readable medium or a signal transmission type medium, for example. 
     Referring to  FIG. 4 , when electrical power is being supplied to the processor  22  ( FIG. 2 ) and the memory  24  ( FIG. 2 ), the processor  22  is directed to perform the steps of a method shown generally at  86 . Method  86  begins at block  88 , which directs the processor  22  to determine the operating mode of the given data acquisition unit  16 . 
     Referring to  FIG. 5 , an exemplary method for performing steps of block  88  is shown generally at  90 . Method  90  begins at block  92 , which directs the processor  22  to determine a power mode of the data acquisition unit  16 . For example, the power mode may be the distributed power mode in which the data acquisition unit  16  is powered by an external power source via the distributed power connector  76  ( FIG. 2 ), or the stand-alone power mode in which the data acquisition unit  16  is self-powered by a stand-alone power source via the battery connector  78  ( FIG. 2 ). The power mode may be determined by determining whether a power conduit is connected to the distributed power connector  76 , whether a stand-alone power source is connected to the battery connector  76 , whether a power supply voltage is present at the distributed power connector  76 , whether a power supply voltage is present at the battery connector  78 , whether a power supply current is flowing through the distributed power connector  76 , whether a power supply current is flowing through the battery connector  78 , or any combination thereof. In at least some embodiments, executing block  92  includes creating, updating or otherwise storing a power mode indicator for subsequent use or retrieval. When block  92  has been executed, the processor  22  is directed to execute block  94 . 
     Block  94  directs the processor  22  to determine a communication mode of the data acquisition unit  16 . For example, the communication mode may be a wired communications mode or a wireless communications mode. In the wired communication mode in accordance with the first embodiment, a wired connection such as the CAN bus  20  ( FIG. 2 ) is received by the data acquisition unit  16  for effecting wired communications via the bus transceiver  70  ( FIG. 2 ). In the wireless communications mode in accordance with the first embodiment, communications are effected via the wireless transceiver  66  ( FIG. 2 ). The communications mode may be determined by determining whether a wired connection is connected to the bus connector  74 , for example. In the first embodiment, the communication mode of the data acquisition unit  16  is the wired communications mode unless no wired connection is available for wired communications, however, other arrangements are possible. In at least some embodiments, executing block  94  includes creating, updating or otherwise storing a communication mode indicator for subsequent use or retrieval. 
     After block  94  has been executed, the processor  22  is then directed to return from the method  90  to the method  86  ( FIG. 4 ) at block  96  thereof. 
     Referring back to  FIG. 4 , block  96  directs the processor  22  to provide a measurement result in accordance with the operating mode, such as that determined by block  88 . Providing the measurement result may include providing a plurality of measurement results, such as by providing a plurality of measurement results from the same or different measurement sensor units, for example. 
     Referring to  FIG. 6 , an exemplary method for performing steps of block  96  is shown generally at  98 . Method  98  begins at block  100 , which directs the processor  22  to determine whether the communication mode of the data acquisition unit  16  is the wired communications mode or the wireless communications mode. Determining which communication mode is active may involve retrieving a communication mode indicator stored by block  94  ( FIG. 5 ), executing or re-executing block  94 , executing or re-executing block  88  ( FIG. 4 ), or any combination thereof for example. 
     If the data acquisition unit  16  is in the wired communications mode, the processor  22  is directed to execute block  102 . 
     Block  102  directs the processor  22  to produce the measurement result in accordance with the wired communications mode. 
     Referring to  FIG. 7 , an exemplary method for performing steps of block  102  is shown generally at  104 . Method  104  begins at block  106 , which directs the processor  22  to select a measurement sensor unit (not shown in  FIGS. 1 to 7 ). The measurement sensor unit can be selected from among any measurement sensor units externally connected to the data acquisition unit  16  at the measurement sensor connectors  32  ( FIG. 2 ). 
     Block  108  then directs the processor  22  to electrically isolate the data acquisition unit  16  from the communications bus in use for wired communications, which may be the CAN bus  20  ( FIG. 1 ). In the first embodiment, isolating the data acquisition unit  16  from the CAN bus  20  may involve opening the bus switch  72 , disconnecting the bus transceiver  70  at the measurement result switch  64 , or any combination thereof for example. Isolating the data acquisition unit  16  from the CAN bus  20  advantageously permits performing measurements without the presence of a ground connection between the data acquisition unit  16  and the building  12  via the CAN bus  20 , thereby removing a possible source of a ground loop connection that could otherwise adversely affect measurement accuracy. 
     Block  110  directs the processor  22  to invoke the selected measurement sensor unit and perform a measurement reading. In the first embodiment, invoking the selected measurement sensor unit involves closing the switching portion  44  ( FIG. 3 ) of the measurement sensor switch  38  corresponding to the measurement sensor connector  32  ( FIG. 2 ) connected to the selected measurement sensor unit. Closing the switching portion  44  permits the power supply voltage to be applied to the selected measurement sensor unit such that a voltage measurable at the buffer amplifier  60  input is indicative of a phenomenon related to the building  12 . 
     In some embodiments, invoking the selected measurement sensor unit involves closing the reference switch  58 , including closing the reference switch  58  for a predetermined amount of time and then opening the reference switch  58 . Having the reference switch  58  closed during a settling time caused by closing the switching portion  44  advantageously reduces the time length of such settling time. 
     In the first embodiment, performing a measurement reading involves storing by the processor  22  in a memory such as the memory  24  the analog-to-digital converter  62  output, which may be considered a digital representation of the measurement result. In the first embodiment, the data acquisition unit  16  is operable to perform a measurement reading while either the reference switch  58  is open or closed. Performing the measurement reading while the reference switch  58  is open causes the measurement reading to be performed on the basis of the reference resistor  50  alone, which in ordinary circumstances advantageously provides a suitable, including possibly an optimal, input voltage level to the analog-to-digital converter  62 . In contrasting circumstances, performing the measurement reading while the reference switch  58  is closed causes the measurement reading to be performed on the basis of the reference resistor  50  in parallel with the second reference resistor  56 , thereby providing a lower voltage input level to the analog-to-digital converter  62 , which in certain circumstances may advantageously provide a voltage input level that is closer to an optimal input voltage level for the analog-to-digital converter  62 . 
     After block  110  has been executed, block  112  directs the processor  22  to re-establish a connection to the communications bus from which the data acquisition unit  16  was isolated by block  108 . In the first embodiment, the processor  22  is directed to re-establish a connection to the CAN bus  20 . Re-establishing the connection to the CAN bus  20  may involve closing the bus switch  72 , re-connecting the bus transceiver  70  at the measurement result switch  64 , or both closing the bus switch  72  and re-connecting the bus transceiver  70  at the measurement result switch  64 . 
     In embodiments and circumstances where multiple measurements are being invoked, the method  104  may include multiple iterations of blocks  106  to  112 , including multiple iterations of blocks  106  to  112  in which a different measurement sensor unit is selected with each iteration, or sequence of iterations, of block  106 . 
     After block  112  has been executed, the processor  22  is then directed to return from the method  104  to the method  98  ( FIG. 6 ) at block  114  thereof. 
     Referring back to  FIG. 6 , block  114  directs the processor  22  to transmit the measurement result, such as that produced by block  112 , to a gateway, such as the gateway  18  ( FIG. 1 ), via the communications bus, such as the CAN bus  20  ( FIG. 1 ). Block  114  is preferably executed in accordance with the wired communications mode, and any suitable wired communications techniques may be employed. 
     In various embodiments, blocks  102  and  114  can be iteratively executed any number of times, including executing blocks  102  and  114  once for each measurement sensor unit connected to the data acquisition unit  16  and including executing blocks  102  and  114  multiple number of times. 
     Block  116  directs the processor  22  to update the profile of the data acquisition unit  16 . In the first embodiment, each data acquisition unit  16  of the system  10  includes a profile for that data acquisition unit  16 . Such profile may include any suitable parameter or other information for directing the operations of the data acquisition unit  16 . For example, the profile may include the amount of time between measurements, or sets of measurements, to be provided by the data acquisition unit  16 , or otherwise direct the frequency at which measurements are to be performed. The profile may include a time stamp for use in synchronizing an internal clock (not shown) of the data acquisition unit  16 . Other profile parameters are possible. 
     In some embodiments, updating the profile includes transmitting to the gateway  18  logged event information, which may include the detection through the use of a measurement sensor unit of a notable fault condition such as a detected leak or extreme value of a measured quantity, for example. In some embodiments, updating the profile also involves activating an indicator, such as a LED (Light Emitting Diode) of the data acquisition unit  16 , to indicate a fault condition, thereby advantageously facilitating locating by personnel the particular data acquisition unit  16  having detected such fault condition. Additionally or alternatively, such indicator at the data acquisition unit  16  may include a graphic visual indicator, such as a display on a LCD (liquid crystal display), audible indicator, tactile indicator such as a vibration, initiation of a mechanical force such as activation of an electromechanical or optical relay, and any combination thereof. 
     Referring to  FIG. 8 , an exemplary method for performing steps of block  116  ( FIG. 6 ) is shown generally at  118 . Method  118  begins at block  120 , which directs the processor  22  to transmit a profile update request. In the first embodiment, the processor  22  is at least operable to transmit the profile update request to the gateway  18  via wired communications along the CAN bus  20 . In some embodiments, transmitting the profile update request also includes transmitting event related information. 
     Block  122  then directs the processor  22  to determine whether a reply has been received in response to the profile update request. In the first embodiment, the data acquisition unit  16  is operable to wait as long as a predetermined amount of time for a reply and, if no reply has been received within such time to determine that no reply is forthcoming. Such amount of time may be selected to provide the gateway  18  with sufficient time to provide a reply in cases where an update to a profile is available, while not unduly delaying the data acquisition unit  16 . The amount of time that a given data acquisition unit  16  will wait before determining that no reply is forthcoming may be a parameter of the profile of that given data acquisition unit  16 . 
     In some embodiments, determining whether a reply is received may include determining that a reply has been received and determining whether the received reply includes a change in the profile. In such embodiments, where a received reply does not indicate any change in the profile, the data acquisition unit  16  is operable to treat such replies as if no reply had been received. 
     If a reply providing a profile, or updated profile, is received, then the processor  22  is directed to execute block  124 . 
     Block  124  directs the processor  22  to store the updated profile in a memory, such as the memory  24 . In at least some embodiments, the updated profile replaces a current profile in the memory  24 . In some embodiments, however, a history of profiles may be stored in the memory  24  for subsequent retrieval and use. 
     After block  124  has been executed, the processor  22  is then directed to return from the method  118  to the method  98  ( FIG. 6 ) at block  126  thereof. 
     Referring back to  FIG. 6 , block  126  directs the processor  22  to reset the timer. In the first embodiment, the timer is reset to a predetermined amount of time in accordance with the profile, including possibly the updated profile obtained by block  116 , of the data acquisition unit  16  such that a next measurement, or set of measurements, is produced after the predetermined amount of time has elapsed. In some embodiments, resetting the timer includes setting the timer to a calculated amount of time that is determined in response to a previously produced measurement result, such as the measurement result most recently produced in accordance with block  102 . Additionally or alternatively, the calculated amount of time may be determined on the basis of a plurality of previously produced measurement results, or an average thereof, produced in accordance with block  102 . Resetting the timer to such calculated amount of time advantageously permits the data acquisition unit  16  to adapt the frequency at which measurement results are produced, thereby facilitating the increased collection of measurement results for critical circumstances while facilitating the decreased collection of measurement results for non-critical circumstances. 
     If at block  100  of  FIG. 6  the processor  22  determines that the communication mode of the data acquisition unit  16  is the wireless communications mode, then the processor  22  is directed to execute block  128 . 
     Block  128  directs the processor  22  to produce the measurement result in accordance with the wireless mode. 
     Referring to  FIG. 9 , an exemplary method for performing steps of block  128  is shown generally at  130 . Method  130  begins at block  132 , which directs the processor  22  to select a measurement sensor unit (not shown in  FIGS. 1 to 9 ). Block  132  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  106  ( FIG. 7 ) described herein above, for example. 
     Block  134  then directs the processor  22  to determine whether the power mode of the data acquisition unit  16  is the distributed mode or the stand-alone mode. Determining which power mode is active may involve retrieving a communication mode indicator stored by block  92  ( FIG. 5 ), by executing or re-executing block  92 , by executing or re-executing block  88  ( FIG. 4 ), or any combination thereof for example. 
     If the data acquisition unit  16  is in the distributed power mode, the processor  22  is directed to execute block  136 . 
     Block  136  directs the processor  22  to electrically isolate the data acquisition unit  16  from any power conduit (not shown) connected to the data acquisition unit  16 , such as any power conduit connected to the data acquisition unit  16  at the distributed power connector  76  ( FIG. 2 ). In the first embodiment, isolating the data acquisition unit  16  from the power conduit involves setting the power mode switch  80  such that the distributed power connector  76  is disconnected from the remainder of the data acquisition unit  16 . Isolating the data acquisition unit  16  from the power conduit advantageously permits performing measurements without the presence of a ground connection between the data acquisition unit  16  and the building  12  via the power conduit, thereby removing a possible source of a ground loop connection that could otherwise adversely affect measurement accuracy. 
     In some embodiments, executing block  136  includes isolating the data acquisition unit  16  from any communications bus connected to the bus connector  74 , such as by executing steps of block  108  ( FIG. 7 ). Additionally or alternatively, executing block  108  may involve isolating the data acquisition unit  16  from any power conduit connected to the data acquisition unit  16  such as at the distributed power connector  76  ( FIG. 2 ). In at least some embodiments, executing blocks  136  and  108  each involve disconnecting both the bus connector  74  and the distributed power connector  76  from the remainder of the data acquisition unit  16 . For example, the bus switch  72  and the power mode switch  80  may both be opened, regardless of whether or not any connections have been made to the bus connector  74  and the distributed power connector  76 . 
     Block  138  then directs the processor  22  to invoke the selected measurement sensor unit and perform a measurement reading. Block  138  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  110  ( FIG. 7 ) described herein above, for example. 
     After block  138  has been executed, block  140  directs the processor  22  to re-establish a connection to the power conduit from which the data acquisition unit  16  was isolated by block  136 . Re-establishing the connection to the power conduit may involve setting the power mode switch  80  such that the distributed power connector  76  is re-connected to the remainder of the data acquisition unit  16 . 
     In some embodiments, executing block  140  includes re-establishing a connection to any communications bus connected to the bus connector  74 , such as by executing steps of block  112  ( FIG. 7 ). Additionally or alternatively, executing block  112  may involve re-establishing a connection to any power conduit connected to the data acquisition unit  16  such as at the distributed power connector  76  ( FIG. 2 ). In at least some embodiments, executing blocks  140  and  112  each involve re-connecting both the bus connector  74  and the distributed power connector  76  to the remainder of the data acquisition unit  16 . For example, the bus switch  72  and the power mode switch  80  may both be closed, regardless of whether or not any connections have been made to the bus connector  74  and the distributed power connector  76 . 
     If at block  134  of  FIG. 9  the processor  22  determines that the power mode of the data acquisition unit  16  is the stand-alone power mode, then the processor  22  is directed to execute block  142 . 
     Block  142  directs the processor  22  to invoke the selected measurement sensor unit and perform a measurement reading. Block  142  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  138 , block  110  ( FIG. 7 ) or both block  138  and block  110 , which are described herein above, for example. 
     Although not shown in  FIG. 9 , the data acquisition unit  16  is in at least some embodiments operable to electrically isolate the distributed power connector  76  from the remainder of the data acquisition unit  16 , such as by executing block  136 , before executing block  142 . Additionally or alternatively, the data acquisition unit  16  is operable to re-establish the connection between the distributed power connector  76  from the remainder of the data acquisition unit  16 , such as by executing block  140 , after executing block  142 . 
     In some embodiments, blocks  136  to  140  are executed instead of block  142  regardless of the power mode of the data acquisition unit  16 . In such embodiments, the method  130  need not include block  134  and the method  130  may proceed directly from block  132  to blocks  136  to  140 . 
     In embodiments and circumstances where multiple measurements are being invoked, the method  130  may include multiple iterations of blocks  132  to  142 , including multiple iterations of blocks  132  to  142  in which a different measurement sensor unit is selected with each iteration, or sequence of iterations, of block  132 . 
     After either block  140  or block  142  has been executed, the processor  22  is then directed to return from the method  130  to the method  98  ( FIG. 6 ) at block  144  thereof. 
     Referring back to  FIG. 6 , block  144  directs the processor  22  of the given data acquisition unit to transmit a beacon request. In the first embodiment, transmitting a beacon request involves transmitting by wireless communications a communication containing a request for identifications of data acquisition units or other devices operable to communicate with the given data acquisition unit  16 , and for the hop count of such other data acquisition units or other devices. Typically, any data acquisition unit  16  in wired communication with the gateway  18  has a hop count of zero. A data acquisition unit  16  operating in the wireless communications mode typically has a hop count of one or greater. In some embodiments, transmitting the beacon request involves transmitting a request for a profile or an update to a profile. 
     Block  146  then directs the processor  22  of the given data acquisition unit  16  to determine whether a reply has been received in response to the beacon request. In the first embodiment, the given data acquisition unit  16  is operable to wait as long as a predetermined amount of time for a reply and, if no reply has been received within such time to determine that no reply is forthcoming. Such amount of time may be selected to provide other data acquisition units  16  in the vicinity of the given data acquisition unit  16  with sufficient time to provide a reply, while not unduly delaying the given data acquisition unit  16 . The amount of time that a given data acquisition unit  16  will wait before determining that no reply is forthcoming may be a parameter of the profile of that given data acquisition unit  16 . Determining whether a reply is forthcoming may include storing information provided in any replies that are received, such by storing identifications and hop counts provided in received replies in a memory such as the memory  24  for subsequent retrieval. 
     If a reply responding to the beacon request is received, then the processor  22  is directed to execute block  148 . In some embodiments where transmitting the beacon request involves transmitting a request for a profile or an update to a profile, executing block  146  may also involve determining whether any reply received in response to the beacon request includes a profile or an update to a profile, and storing the profile or update thereof. Additionally or alternatively, a profile may be updated by the execution of further blocks described herein below. 
     Block  148  directs the processor  22  to transmit the measurement result to a preferred recipient. 
     Referring to  FIG. 10 , an exemplary method for performing steps of block  148  ( FIG. 6 ) is shown generally at  150 . Method  150  begins at block  152 , which directs the processor  22  of the given data acquisition unit  16  to determine the number of available recipients having a lowest hop count. In the first embodiment, such available recipients are other data acquisitions units  16  or other devices operable to communicate with the given data acquisition unit  16  that have provided to the given data acquisition unit  16  a reply to the beacon request transmitted in accordance with block  144  ( FIG. 6 ). In the first embodiment, the given data acquisition unit  16  is operable to compare hop counts contained in replies received in response to the beacon request such that a lowest hop count may be determined. 
     For example, if 6 replies from available recipients are received, 3 of which specify hop counts of one, 2 of which specify hop counts of two, and 1 of which specifies a hop count of three, then the lowest hop count is one. In such example, executing block  152  results in the determination of 3 as the number of available recipients having the lowest hop count of one. Other determinations are possible, including determining any plural number of available recipients have a lowest hop count and determining that only one available recipient has a lowest hop count. 
     After block  152  is executed, the processor  22  is directed to execute block  154 . 
     Block  154  directs the processor  22  to determine whether a plural number was determined by block  152 . 
     If the number of available recipients having a lowest hop count is not a plural number, the processor  22  is directed to execute block  156 , which directs the processor  22  to select the recipient having the lowest hop count. In the first embodiment, the selected available recipient is the one available recipient having provided in a reply to the beacon request a hop count lower than all other hop counts contained in any other replies received in response to the beacon request. 
     If the number of available recipients having a lowest hop count is a plural number, then the processor  22  is directed to execute block  158 , which directs the processor  22  to select, from among that plural number of available recipients having the lowest hop count, the one available recipient having the signal strength. In the first embodiment, the given data acquisition unit  16  is operable to determine a wireless communications signal strength corresponding to replies received by wireless communications in response to the beacon request. Such wireless communications signal strength may be determined by RSSI (Received Signal Strength Indication) technology, for example. In the first embodiment, the given data acquisition unit  16  is advantageously operable to select a nearest neighbour, as measured by signal strength, among neighbouring data acquisition units  16  having a minimal hop count, thereby enhancing wireless communications between the given data acquisition unit  16  and the gateway  18 . Additionally or alternatively, the given data acquisition unit  16  is operable in some embodiments to select a nearest neighbour geographically by determining or receiving the location of one or more other data acquisition units  16 . The location of such other data acquisition units  16  may be determined by the use of a GPS (Global Positioning System) or similar. 
     After either block  156  or block  158  has been executed, the processor  22  is directed to execute block  160 . 
     Block  160  directs the processor  22  to transmit the measurement result to the selected recipient. In the first embodiment, the given data acquisition unit  16  is operable to transmit the measurement result obtained by block  128  ( FIG. 6 ) to the available recipient selected by executing either block  156  or block  158 . Such transmission in the first embodiment is preferably by wireless communications in accordance with the identification contained in the reply to the beacon request received from the selected available recipient. 
     In the first embodiment, executing block  160  also involves transmitting an identification of the source of the communication, which by way of example may be the given data acquisition unit  16  having produced the measurement result in accordance with block  128  ( FIG. 6 ). 
     After executing block  160 , the method  150  ends and the process returns to the method  98  ( FIG. 6 ) at block  162 . 
     Referring back to  FIG. 6 , block  162  directs the processor  22  to update the profile. In some embodiments, the profile may be updated by executing blocks  144  and  146 , for example. In such embodiments, block  162  may not need to be executed, but may be executed in addition to executing blocks  144  and  146 . 
     Referring to  FIG. 8 , an exemplary method for performing steps of block  162  ( FIG. 6 ) is shown generally at  118 . Method  118  begins at block  120 , which directs the processor  22  to transmit a profile update request. In the first embodiment, the processor  22  is operable to transmit the profile update request to the gateway  18  via wired communications along the CAN bus  20 , and is also operable to transmit the profile update request to the gateway  18  via wireless communications with the preferred recipient selected in accordance with block  148  ( FIG. 6 ). Typically, a given data acquisition unit  16  will transmit the profile update request via wired communications when in the wired communications mode and will transmit the profile update request via wireless communications when in the wireless communications mode. In the wireless communications mode, the given data acquisition unit  16  preferably transmits the profile update request to the preferred recipient, which then re-transmits the profile update request toward the gateway  18 . Further re-transmissions may occur depending on the arrangement of data acquisition units  16  in a given system  10  installation. In the first embodiment, transmitting a profile update request in accordance with block  120  involves determining which communication mode is active, such as by executing block  100  ( FIG. 6 ) and transmitting the profile update request in accordance with the active communication mode. 
     After block  120  has been executed, then block  122  is executed and block  124  is executed if block  122  determines that a reply has been received, as described in further detail herein above. Thereafter, the method  118  ends and the processor  22  is directed to return to processing the method  98  ( FIG. 6 ) at block  164 . 
     In some embodiments where transmitting a beacon request, such as by executing block  144  ( FIG. 6 ) involves transmitting a request for a profile or an update to a profile, then method  188  may involve executing block  124  only, for example. In some embodiments, 
     Referring back to  FIG. 6 , block  164  directs the processor  22  to reset the timer. Block  164  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  126  described herein above. For example, the data acquisition unit  16  is operable to reset the timer in accordance with the profile, including possibly the updated profile obtained by block  162 , of the data acquisition unit  16 . By way of further example, the data acquisition unit  16  is operable in at least some embodiments to set the timer to a calculated amount of time that is determined in response to one or more measurement results produced in accordance with block  128 . 
     Block  166  then directs the processor  22  to set the power state of the data acquisition unit  16 . 
     Referring to  FIG. 11 , an exemplary method for performing steps of block  166  ( FIG. 6 ) is shown generally at  168 . Method  168  begins at block  170 , which directs the processor  22  to determine which power mode is active. In the first embodiment, the power mode is either the distributed power mode or the stand-alone power mode. However, other power modes are possible. 
     In the first embodiment, if the stand-alone power mode is active the processor  22  is directed to execute block  172 . Block  172  directs the processor  22  to reconfigure pins of the processor  22  for low leakage. By way of example, the memory  24  may contain information, such as in a look-up table, of the various possible states of processor  22  pins and/or an indication as to which state for each processor  22  pin is associated with a lowest leakage current through that pin. In some embodiments, executing block  172  involves configuring pins of multiple integrated circuits of the data acquisition unit  16  for low leakage. Executing block  172  advantageously minimizes leakage current during the duration of a low power state of the data acquisition unit  16 . 
     Block  174  then directs the processor  22  to set the power state of the data acquisition unit  16  to the low power state. In the first embodiment, such low power state may be considered a sleep state of the processor  22  and other integrated circuits of the data acquisition unit  16 . Block  174  advantageously minimizes power usage in the stand-alone power mode while the data acquisition unit  16  awaits in accordance with the predetermined amount of time before the next measurement, or set of measurements, is produced. 
     In the first embodiment, if the distributed power mode is active the processor  22  is directed to end the method  168 . For a given data acquisition unit  16  in the distributed power mode, not entering the low power state in the distributed power mode advantageously permits the given data acquisition unit  16  to be available for receiving communications from other data acquisition units  16  or other devices operable to communicate with the given data acquisition unit  16 . In some embodiments, the given data acquisition unit  16  is operable to enter the low, or a lower, power state in the distributed power mode while still retaining the ability to receive communications from other devices, and to re-enter full power mode when needed to act upon such received communications or request a retransmission of such received communications. In some embodiments, the data acquisition unit  16  is operable to enter a low, or lower, power state regardless of the power mode. Conversely, in some embodiments the data acquisition unit  16  is operable to refrain from entering a low, or lower, power state regardless of the power mode. 
     After block  174 , or block  170  in the distributed power mode, has been executed, the processor  22  is directed to return from the method  168  to the method  98  ( FIG. 6 ) following block  166  thereof. 
     If at block  146  of  FIG. 6  the processor  22  determines that no reply in response to the beacon request (block  144 ) has been received, then the processor  22  is directed to execute block  176 . 
     Block  176  directs the processor  22  to store the measurement result, which may be the measurement result produced by block  128 . In the first embodiment, the data acquisition unit  16  is operable to store the measurement result in the memory  24 . In some embodiments, the data acquisition unit  16  is operable to store a measurement count in association with the measurement result such that, upon re-establishment of wireless communications, all stored measurement results can be provided to the gateway  18  in association with a measurement count. In the first embodiment, the gateway  18  is operable to determine, such as by retrieval from a database (not shown in the Figures) of or in communication with the gateway  18 , the predetermined amount of time elapsed between each measurement, or set of measurements, produced by the data acquisition unit  16 , thereby permitting the gateway  18  to track the times at which all measurements provided by the data acquisition unit  16  were produced. In some embodiments, the data acquisition unit  16  need only provide to the gateway  18  the order in which the measurements, or sets thereof, were produced for the gateway  18  to be able to back-calculate the time at which each measurement, or set of measurements, were produced. For example, upon re-establishment of wireless communications, the data acquisition unit  16  may be operable to transmit measurement results in the order in which they were produced. In some embodiments, the data acquisition unit  16  is operable to time stamp each measurement, such as by associating current time information with each measurement produced by the data acquisition unit  16 , thereby relieving the gateway  18  of the task of calculating measurement times from an associated order of measurements or associated measurement counts. Additionally or alternatively, the time at which the gateway  18  ( FIG. 1 ) receives a measurement, or set of measurements, may be determined and possibly tracked or otherwise stored for subsequent use, including possibly being tracked by the gateway  18  and not tracked by the data acquisition unit  16 . In some embodiments, the time at which a measurement, or set of measurements, is produced is not tracked. 
     Block  178  then directs the processor  22  to reset the timer. Block  178  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  126 , block  164 , or both block  126  and block  164 , described herein above. For example, the data acquisition unit  16  is operable to reset the timer in accordance with a previously stored profile of the data acquisition unit  16 , without updating the profile if wireless communications are unavailable. 
     In some embodiments, a given data acquisition unit  16  is operable to reset the timer in accordance with a stored timing value regardless of any timing value contained within the profile for that given data acquisition unit  16 . In such embodiments, the system  10  is operable to provide the same timing value contained within the same or different profiles to a plurality of data acquisition units  16 , while permitting particular ones of the plurality to ignore the timing value contained within the received profile. The particular ones of the plurality may be selected in accordance with the particular measurement sensor units connected and in use by such particular data acquisition units  16 , for example. 
     Block  180  then directs the processor  22  to set the power state of the data acquisition unit  16 . Block  180  may be implemented in any suitable manner, including a manner identical, similar, analogous or different to the implementation of block  166  described herein above. 
     Still referring to  FIG. 6 , in the first embodiment executing block  148  also involves transmitting any previously stored measurement results with the current measurement result to the preferred recipient, thereby advantageously providing past measurements results upon re-establishment of communications. 
     In variations of embodiments, the data acquisition unit  16  is operable to store measurement results and provide a set of such measurement results regardless of whether communications are temporarily suspended. In such embodiments, blocks  144  to  148  and  162  to  166  need not be executed during iterations of the method  98  in which such set of measurement results are not being provided to the gateway  18 . In some embodiments, the data acquisition unit  16  is operable to provide an event indicator in addition or in the alternative to providing a measurement result or set thereof. For example, the data acquisition unit  16  could provide an alarm indication upon one or more measurement results, including an average of such measurement results, that exceed a specifiable threshold. In some embodiments, each measurement result provided by the data acquisition unit  16  is an average of a plurality of results of measurements performed in accordance with method steps described herein. 
     In some embodiments, block  146  and blocks  176  to  180  are not executed for each new iteration of the method  98 . In such embodiments, after block  128  has been executed the processor  22  is directed to execute block  148 , followed by blocks  162  to  166 . In some embodiments, the method  98  involves transmitting a beacon request until a first reply is received, determining the preferred recipient, and storing identification information associated with such preferred recipient for subsequent iterations of block  148 . In such subsequent iterations of block  148 , the data acquisition unit  16  need not execute blocks  146  and  176  to  180 . In some embodiments, the preferred recipient is stored within the memory  24  upon installation and blocks  146  and  176  to  180  are never executed. Other variations of the method  98  are possible. 
     After any one of blocks  126 ,  166  or  180  has been executed, the processor  22  is directed to end the method  98  and return to the method  86  ( FIG. 4 ) following block  96 . 
     Referring back to  FIG. 4 , after block  96  has been executed, the processor  22  is directed to end the method  86 . In the first embodiment, the data acquisition unit  16  is operable to start the method  86  after the predetermined amount of time to which the timer had been set by any one of blocks  126 ,  164  or  178  has elapsed, thereby advantageously permitting the data acquisition unit  16  to provide a measurement result, or set of measurement results, at predetermined intervals of time. In the first embodiment, such predetermined intervals of time are adjustable in accordance with steps for updating the profile of the data acquisition unit. 
     While  FIG. 4  shows block  88  being executed in its entirety prior to block  96  being executed, other arrangements are possible. For example, the determination of either or both of the power mode and the communication mode may be delayed until needed. In variations, block  92  can be executed at any time prior to or concurrent with executing block  134  ( FIG. 9 ) and/or block  170  ( FIG. 11 ). Similarly, block  94  of  FIG. 4  may be executed at any time prior to or concurrent with executing block  100  ( FIG. 6 ) and/or block  190  ( FIG. 12 ). 
     Referring to  FIG. 12 , an exemplary method in accordance with the first embodiment of the invention is shown generally at  182 . The method  182  advantageously permits a given data acquisition unit  16  to receive and act upon communications received from other data acquisition units  16  or other devices operable to communicate with the given data acquisition unit  16 . In accordance with the first embodiment, the given data acquisition unit  16  is operable to receive such communications by wireless transmission while in the full power state. However, other arrangements are possible. 
     The method  182  begins at block  184 , which directs the given data acquisition unit  16  to receive a communication from a transmitting data acquisition unit  16 . In the first embodiment, the communication includes an identification of a source of the communication, which may be the transmitting data acquisition unit  16 . Additionally or alternatively, the source of the communication may be a first transmitting data acquisition unit  16  in a chain of transmitting data acquisition units  16 , for example. 
     Block  186  then directs the processor  22  to determine whether or not the transmitted communication is a beacon request, such as a beacon request transmitted in accordance with block  144  ( FIG. 6 ). Block  186  advantageously permits the given data acquisition unit  16  to reply to beacon requests and to re-transmit communications intended for the gateway  18 . 
     If the transmitted communication is a beacon request, block  188  directs the processor  22  to reply to the transmitting data acquisition unit  16  with the identification and hop count of the given data acquisition unit  16 . Block  188  advantageously permits the transmitting data acquisition unit  16  to include the given data acquisition unit  16  in its selected of a preferred recipient in accordance with block  148  ( FIG. 6 ), for example. In some embodiments, replying to the transmitting data acquisition unit  16  includes transmitting a profile, such as a copy of the profile in use by the given data acquisition unit  16 . In such embodiments, separately updating the profile may not need be performed, but may be performed in addition to the communications associated with beacon requests and corresponding replies. 
     If the transmitted communication is not a beacon request, block  190  directs the processor  22  to determine which communication mode is active for the given data acquisition unit  16 . 
     If by block  190  the processor  22  determines that the given data acquisition unit  16  is operating in the wired communication mode, the processor  22  is directed to execute block  192 . 
     Block  192  directs the processor  22  to transmit the transmitted communication and an identification of the source of the communication to the gateway  18  via the bus, such as the CAN bus  20 . In the first embodiment, the originating data acquisition unit  16  is operable when transmitting a communication toward the gateway  18 , for example by transmitting the communication to its preferred recipient such as in accordance with block  148  ( FIG. 6 ), to also transmit its identification. In accordance with block  192 , the given data acquisition unit  16  having received the transmitted communication is operable to re-transmit the communication and the identification of the source of the communication. Doing so may involve replacing its own identification in its own data packet headers with the identification contained within the data packet header of the transmitted communication received by it, thereby advantageously transmitting an identification of the source of the communication while minimizing data transmission overhead. 
     If by block  190  the processor  22  determines that the given data acquisition unit  16  is operating in the wireless communication mode, the processor  22  is directed to execute block  194 . 
     Block  194  directs the processor  22  of the given data acquisition unit  16  to transmit the transmitted communication and an identification of the source of the communication to a preferred recipient selected by the given data acquisition unit  16 . The preferred recipient may be selected in any suitable manner, including a manner identical, similar, analogous or different to the manner in which a preferred recipient is selected in accordance with the method  150  ( FIG. 10 ) described herein above. 
     After any one of blocks  188 ,  192  or  194  has been executed, the processor  22  is directed to end the method  182 . 
     Thus, there is provided a method of monitoring a structure, the method comprising: (a) receiving at a first connector of a measurement acquisition unit a sensor unit electrically connected to the structure; and (b) invoking said sensor unit so as to produce a measurement result for monitoring the structure, wherein invoking said sensor unit so as to produce a measurement result for monitoring the structure comprises electrically isolating a second connector of said measurement acquisition unit from said first connector. 
     Prior Art Leak Detection Tape 
     Referring to  FIGS. 13 and 14 , a prior art leak detection tape  200  having a plurality of probes  202  inserted through a pair of spaced apart conductors  204  and a substrate  206  is shown. The pair of conductors  204  are attached at one end to a cable  208  and unattached at the opposing end. The electrical resistance measured between the pair of conductors  204  is ordinarily infinite (i.e. an open circuit). However, when a liquid such as water is disposed across the pair of conductors  204 , the electrical resistance becomes very low (i.e. a short circuit condition results), thereby detecting the presence of the liquid. 
     A cross sectional view of the prior art leak detection tape  200  is shown in  FIG. 14 . The leak detection tape  200  includes an adhesive layer  210  for adhering the back of the leak detection tape  200  to the surface of a floor  212  (not shown). 
     The probes  202  are nails or screws inserted into the floor  212 . If the floor  212  becomes moist, such moisture content of the floor  212  lowers the electrical resistance between the probes  202 , thereby measuring moisture content of the floor  212 . 
     Measurement Sensors 
     A measurement sensor for monitoring a structure includes: (a) measurement sensing means for measuring a feature of the structure; and (b) connection test means for indicating an impaired connection of said measurement sensor, said connection test means being electrically connectable in parallel with said measurement sensing means and having a finite impedance such that when said connection test means is connected an impedance of said measurement sensor greater than said finite impedance indicates said impaired connection. 
     Referring to  FIG. 15 , an encloseable moisture content sensor in accordance with embodiments of the invention is shown generally at  214 . The inventive encloseable moisture content sensor  214  includes two spaced apart adhesive layers  216  at opposing sides along the encloseable moisture sensor  214 . The pair of adhesive layers  216  are disposed on the front of the encloseable moisture sensor  214  in conjunction with a pair of spaced apart conductors  218 , which are attached to a backing material  220 . In variations of embodiments, the pair of adhesive layers  216  may be disposed along any portion of the backing material, including being disposed along the entire front surface of the backing material  216  so as to form a single adhesive layer. The adhesive layers  216  may include adhesive suitable for adhering the conductors  218  to the backing material  220  along its front surface. The encloseable moisture content sensor  214  preferably also includes one or more peel-off layers (not shown) for protecting the pair of adhesive layers prior to installation. 
     The encloseable moisture content sensor  214  in at least some embodiments is dimensioned to permit probes (not shown) to be inserted through the backing material  220  into the surface of a building material  222 , which may be a wall, floor, ceiling and/or roof, frame member, joist or similar for example. The encloseable moisture content sensor advantageously facilitates the measurement of moisture content of the building material  222  while avoiding inaccuracies in such measurement that may be caused by substances external to the building material  222 , including dust, oil, grease or fluids for example. The encloseable moisture content sensor  214  is dimensioned for connection to a device, such as the data acquisition unit  16  ( FIGS. 1 and 2 ) described herein above, operable to perform measurements, such as by invoking the encloseable moisture content sensor  214  and performing a measurement reading therefrom. 
     Referring to  FIGS. 16 and 17 , a moisture content sensor in accordance with embodiments of the invention is shown generally at  224 . The inventive moisture content sensor  224  includes an enclosure made of an electrically insulating material, such as the electrically insulating housing  226  shown in  FIGS. 16 and 17 . Within the housing  226  are disposed a pair of spaced apart conductors  228  best seen in the cross sectional view of  FIG. 17 . In some embodiments, the housing  226  forms a sheath around each of the conductors of the pair  228 . Such conductors may be made of any suitable electrically conductive material, including being single or multi-strand copper wires or strips, for example. The moisture content sensor  224  is dimensioned for connection to a device, such as the data acquisition unit  16  ( FIGS. 1 and 2 ) described herein above, operable to perform measurements, such as by invoking the moisture content sensor  224  and performing a measurement reading therefrom. 
     The moisture content sensor  224  is preferably able to receive one or more probe supports such as the eyelet rivets  230  shown in  FIGS. 16 and 17 . Each eyelet rivet  230  is dimensioned to be able to receive a probe  232 , which may be any electrically conductive object suitable for inserting through the eyelet rivet  230  into a building  12  material. Examples of probes  232  include nails, screws, bolts, male rivets, staples, pegs, needles and other electrically conductive objects. The probe supports of the moisture content sensor  224  are preferably attachable to the housing  226  in a manner that facilitates manufacturing of the moisture content sensor  224 , such as by riveting the probe supports to the housing  226 . The use of eyelet rivets  230  that can be riveted to the housing  226  advantageously facilitates manufacturing of the moisture content sensor  224 . The eyelet rivets  230  may be located anywhere along the conductors  228 , including being located in transverse alignment to each other. The eyelet rivets  230  may be attached to the moisture content sensor  224  by any suitable technique, including by riveting for example. 
     In some embodiments, the housing  226  includes one or more perforations (not shown), such as holes, slits, cuts or similar, to selectively exposing the pair of conductors  228 . The perforations may be regularly spaced apart along the length of the housing  226 , for example. The perforations may advantageously facilitate the detection by the moisture content sensor  224  of surface moisture such as leaks, flood conditions, etc. In embodiments where the housing  226  includes both perforations and probe supports, the perforations are typically not in contact with the probe supports. 
       FIGS. 18   a  to  18   e  show variations of a measurement sensor  234  in accordance with embodiments of the invention. Each measurement sensor  234  includes a pair of spaced apart conductors  236  having a cable  238  attached at a connection end  240  of the measurement sensor  234 . The measurement sensor  234  at its connection end  240 , the cable  238  at least one end thereof, or both the measurement sensor  234  at its connection end  240  and the cable  238  are dimensioned for connection to a device, such as the data acquisition unit  16  ( FIGS. 1 and 2 ) described herein above, that is operable to perform measurements, such as by invoking the measurement sensor  234  and performing a measurement reading therefrom. Not all embodiments need include the cable  238 . Probes  242  are shown attached, inserted through or otherwise in electrical contact with the conductors of the pair  236 . In some embodiments, the measurement sensor  234  includes an electrically insulating substrate (not shown) for supporting the pair of conductors  236 , and such substrate may be adhesive-backed and include a peel-off layer. 
     Each measurement sensor  234  includes at a terminal end  244  opposite to the connection end  240  an impedance circuit, which may include any combination of electrical components or circuitry, for example. Exemplary impedance circuits include the reference impedance  246  shown in  FIG. 18   a , the thermistor  248  shown in  FIG. 18   b , the diode  250  shown in  FIG. 18   c , the dual reference impedance circuit  252  shown in  FIG. 18   d , and the first reference impedance  246  and the second reference impedance  246  shown in  FIG. 18   e . One or more impedance circuits may be electrically connected in parallel with the pair of conductors  236  including as shown in  FIGS. 18   a  to  18   e . A connected impedance circuit preferably has a finite impedance such that the parallel impedance of the pair of conductors  236  in parallel with the connected impedance circuit indicates an impairment of an electrical connection of the measurement sensor  234  if the parallel impedance is greater than the finite impedance of the connected impedance circuit alone. Although  FIGS. 18   a  to  18   e  show the impedance circuit connected to the measurement sensor  234  at the terminal end  244 , in general the impedance circuit may be applied at either or both ends of the measurement sensor  234  or cable  238  thereof, at either or both ends of the moisture content sensor  224  ( FIGS. 16 and 17 ), at either or both ends of the encloseable moisture content sensor  214  ( FIG. 15 ), or any combination thereof. 
     Referring to  FIG. 18   a , the reference impedance  246  may have any suitable finite impedance. In some embodiments, the reference impedance  246  will vary with frequency and may only be a finite impedance within a specifiable frequency range. The reference impedance  246  advantageously permits a device such as the data acquisition unit  16  ( FIGS. 1 and 2 ) to determine whether an electrical connection between the device and the reference impedance  246  has been impaired, including detecting a complete disconnection. The measurement sensor  234 , including the reference impedance  246 , is generally able to receive from the device a DC voltage, DC current, AC voltage, AC current, a waveform such as a pulse, or other electrical stimulation. For example, the measurement sensor  234  may be invoked by the application of a DC voltage, in which case insufficient current resulting therefrom indicates an impaired connection between the device and the reference impedance  246 . Such impaired connection may be at the connection between the device and the measurement sensor  234 , within the cable  238  if present, at the connection between the cable  238  and the pair of conductors  236 , along the pair of conductors  236 , at the connection between the pair of conductors  236  and the reference impedance  246 , within the reference impedance  246 , or any combination thereof. By way of further example, the exact location of an impaired connection or an indication that no impaired connection exists can be determined by applying a time-domain reflectometry (TDR) waveform to the measurement sensor  234  for a TDR measurement. In some embodiments, the reference impedance  246  has a precision impedance value, possibly including a precision resistance value, to facilitate use of the measurement sensor  234  when no impairment of electrical connectivity is occurring. Additionally or alternatively, in some embodiments the impedance value of the reference impedance  246  can be calibrated for use with the device. 
     Referring to  FIG. 18   b , the thermistor  248  is a particular example of the reference impedance  246  ( FIG. 18   a ) in which the resistance thereof varies with temperature. In addition to the advantage of permitting a device to determine whether a connection impairment is present, the thermistor  248  advantageously provides an indication of temperature when no connection impairment is present, while permitting leak detection and/or moisture content measurements to be performed. Preferably, the variation of resistance with changes in temperature, within an expected temperature range, of the thermistor  248  is small compared to the variation in resistance or impedance of the pair of conductors  236  with changes in moisture content or between the presence and absence of a detectable fluid leak, thereby advantageously providing connection impairment detection and temperature measurement with minimal impact on moisture content and/or leak detection accuracy. 
     Referring to  FIG. 18   c , the diode  250  is another particular example of the reference impedance  246  ( FIG. 18   a ) in which the impedance thereof varies with polarity of applied voltage. As is well known in the art, a diode provides a low impedance (e.g. short circuit) when a sufficient voltage is applied in a forward diode direction and provides a high impedance (e.g. open circuit) when a voltage is applied in the opposing reverse diode direction. The diode  250  advantageously permits the determination of a connection impairment when the sufficient voltage is applied in the forward diode direction and advantageously permits the performance of a measurement with minimal or no effect by the diode  250  when a voltage is applied in the reverse diode direction. 
     Referring to  FIG. 18   d , the dual reference impedance circuit  252  is a general example of the reference impedance  246  ( FIG. 18   a ) that advantageously presents a first reference impedance when a stimulus having a first polarity is applied and a second reference impedance when a stimulus having a second polarity is applied. By way of example, the first reference impedance may be a precision resistor for use in performing measurements, such as moisture content and/or leak detection measurements, and the second reference impedance may be a thermistor for providing a temperature measurement. By way of further example, the first and second reference impedances may be first and second resistors having different first and second resistance values for providing different first and second sensor output voltage ranges, respectively. By way of further example, the system  10  is advantageously operable to perform a continuity check of the measurement sensor  236 , and the first or second reference impedance may have any impedance suitable for performing such continuity check including possibly a fixed resistive impedance such as a minimal or zero ohms resistance. Other circuitry possibilities exist and, in general, each of the first and second reference impedances may be any electrical components or combinations of electrical components. In the embodiment shown in  FIG. 18   d , one capacitor is in parallel with each diode  251  and each diode  253  to advantageously provide noise suppression, including possibly noise suppression at 50 Hz and/or 60 Hz frequency, which may advantageously enhance measurement and detection accuracy. However, not all embodiments need to have all such capacitors and any number of capacitors may be present or absent from the dual reference impedance circuit  252 . While  FIG. 18   d  shows two parallel sub-circuits or paths having two diodes  251  and two diodes  253  in each of the parallel paths of the dual reference impedance circuit  252 , any number of one or more diodes in each path may be present in various embodiments of the invention. While  FIG. 18   d  shows the dual reference impedance circuit  252  having two paths thereof, any number of one or more paths may be present in various embodiments. While  FIG. 18   d  shows both paths connected at the terminal end  244  of the pair of conductors  236 , in various embodiments both paths may be connected at the connection end  240  of the pair of conductors  236 . Additionally or alternatively, one path may be connected at the connection end  240  and the other path connected at the terminal end  244 . 
     Referring to  FIGS. 18   d  and  18   e , either or both of the first reference impedance and the second reference impedance shown in  FIG. 18   d  may be implemented as a pair of conductors  236 , which may be terminated by a reference impedance  246 . By way of exemplary illustration,  FIG. 18   e  shows diodes  251  and diodes  253  arranged at connection ends  240  of two pairs of conductors  236 . At the terminal ends  244  of each of the two pairs of conductors  236  is connected a reference impedance  246 . Typically the reference impedances  246  have different impedance values Z A  and Z B  as shown in  FIG. 18   e . However, in general each of the reference impedances  246  may have any impedance value and preferably have the same or different finite impedance values. Preferably, the reference impedances  246  shown in  FIG. 18   e  are each a single resistive element such as a resistor, including possibly a precision resistor. The reference impedances  246  advantageously permit a data acquisition unit  16  to which the measurement sensor  234  is connected to perform a continuity check or otherwise test for an impaired connection. While not shown in  FIG. 18   e , in some embodiments capacitors, such as for reducing noise, are included in parallel with one or more of the diodes  251  and  253  in a manner similar to that shown in  FIG. 18   d.    
     The two diodes  251  shown in  FIG. 18   d , and the two diodes  251  shown in  FIG. 18   e , are directed in the same electrical flow direction as each other. Similarly, the two diodes  253  shown in each of  FIGS. 18   d  and  18   e  are directed in the same direction as each other. The diodes  251  are directed in the opposing direction to that of the diodes  253 , thereby advantageously providing selectivity. In  FIG. 18   d , reference impedance selectivity is provided, while in  FIG. 18   e  conductor  236  pair selectivity, in conjunction with its respective termination, is provided. In variations, only one diode  251  and/or only one diode  253  need be included in any given path of the measurement sensors  234  shown in  FIGS. 18   d  and  18   e  to achieve selectivity. 
     Referring to  FIGS. 19   a  and  19   b , a termination module in accordance with embodiments of the invention is shown generally at  254 . The termination module  254  includes a base such as the printed circuit board (PCB)  256  having a pair of apertures  258  therethrough for receiving a pair of probes  260 . The termination module  254  includes a termination circuit  262  dimensioned for electrical contact with the probes  260  when being received by the termination module  254 . In some embodiments, the termination module  254  includes probe supports (not shown) for facilitating electrical contact between probes  260  being received by the termination module  254  and the termination circuit  262 . Such probe supports may be implemented in any suitable manner, including as eyelet rivets, PCB vias, metallic linings, or any combination thereof for example. Such probe supports may be attached to the termination module  254  by any suitable technique, including by riveting for example. The termination circuit  262  may be any electrical circuit, including in some embodiments an impedance circuit ( FIGS. 18   a  to  18   d ) such as the reference impedance  246 , thermistor  248 , diode  250 , dual reference impedance circuit  252 , or any combination thereof for example. The termination circuit  262  preferably has a finite impedance, including possibly a nonlinear impedance, such that the termination circuit  262  advantageously permits detection of a connection impairment. Circuit traces of the impedance circuit may be disposed within the PCB  256 , coated with an insulating material, or otherwise protected from dust or other undesirable sources of electrical connectivity. In the embodiments shown in  FIGS. 19   a  and  19   b , the termination module  254  includes a temperature sensor  264 , which may be implemented as a thermistor for example. The temperature sensor  264  is operable to provide an indication of temperature to a connected device by way of the temperature wires  266 , which may include any number of wires and/or wired connections. 
     The pair of probes  260  may be inserted through the pair of apertures  258  into a building  12  material. Wires (not shown in  FIGS. 19   a  and  19   b ) in electrical contact with each of the probes  260 , such as by making electrical contact with electrically conductive portions of the termination circuit  262  at the apertures  258 , may be connected, including being connected in conjunction with the temperature wires  266 , to a device such as the data acquisition unit  16  ( FIGS. 1 and 2 ), such that the termination module may advantageously be used as a measurement sensor, including as a moisture content and temperature sensor. 
     However, not all embodiments of the termination module  254  need include wires providing direct electrical contact between a measurement device and the probes  260 . In some embodiments, the apertures  258  are dimensioned in various embodiments to correspond to the spacing between conductors of measurement sensors, such as the conductors  268  of the leak detection and moisture content measurement sensor  270  shown in  FIG. 19   b . The leak detection and moisture content measurement sensor  270  may include an electrically insulating substrate (not shown) for supporting the conductors  268 , and such substrate may be adhesive-backed and include a peel-off layer. 
     When the probes  260  are being received by the apertures  258 , the probes  260  are appropriately spaced to make electrical contact with the conductors  268  and are insertable into building  12  material so as to secure the termination module  254  in place. The termination module  254  advantageously provides ease of installation of the termination circuit  262 . One or more termination modules  254  may be installed at any location or locations suitable for receiving the pair of probes  260 , including at any points along the pair of conductors  218  ( FIG. 15 ), conductors  228  ( FIGS. 16 and 17 ), conductors  236  ( FIGS. 18   a  to  18   e ) and conductors  268  of the leak detection and moisture content measurement sensor  270 . Where the termination module  254  is received by eyelet rivets  230  ( FIGS. 16 and 17 ) of the moisture content sensor  224 , such eyelet rivets  230  are preferably in transverse alignment with each other. 
     Referring to  FIG. 20   a , the termination module  254  includes in some embodiments a cable housing  272  for housing the termination circuit wires  274  and the temperature wires  266 . The cable housing  272  advantageously facilitates use of the termination module  254  as a moisture content and/or temperature sensor. In general, either or both of the termination circuit  262  and the temperature sensor  264  may be included in the termination module  254 . The cable housing  272  and termination circuit wires  274  arrangement advantageously facilitates use of the termination module  254  to provide a connection between a measurement device and a connection end of any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), the measurement sensor  234  ( FIGS. 18   a  to  18   e ) and the leak detection and moisture content measurement sensor  270  ( FIG. 19   b ). However, the termination module  254  may be located at any point along such sensors. 
       FIG. 20   b  shows a condensation sensor  276  to which the termination module  254  having the exemplary cable housing  272  is shown attached. In various embodiments, the condensation sensor  276  may include the termination module  254  attached at any point along the condensation sensor  276 , including at either end thereof. In some embodiments, the condensation sensor  276  does not include a termination module  254 . The condensation sensor  276  may, but need not, include probes (not shown in  FIG. 20   b ) for measuring moisture content within a building  12  material. In various embodiments, one or more termination modules  254 , each of which being with or without the cable housing  272 , are attachable at any point(s) along any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), the measurement sensor  234  ( FIGS. 18   a  to  18   d ), the leak detection and moisture content measurement sensor  270  ( FIG. 19   b ) and the condensation sensor  276 . 
     The condensation sensor  276  includes a pair of spaced apart conductors  278 , and a layer of non-hydrophobic material  280  in physical contact with the respective top surfaces of the conductors of the pair  278 . The non-hydrophobic material  280  is preferably electrically insulating, and may be made of a woven or fibrous material, such as a woven polymer. The non-hydrophobic material  280  may be made of a polyester, for example. The non-hydrophobic material  280  may have any length, including a calibrated or otherwise specifiable length for example. The non-hydrophobic material  280  may extend along any portion of the pair of conductors  278 , including extending along the entire length of the pair of conductors  278 . The non-hydrophobic material  280  is preferably suitable for collecting moisture external to a building  12  material, such as moisture produced by condensation, and typically does so by providing an increased surface area where fluid or other moisture may collect. Typically, the non-hydrophobic material  280  is also non-hygroscopic such that collected moisture is not absorbed by the non-hydrophobic material  280 , thereby facilitating the detection by the condensation sensor  276  of the collected moisture. Such non-hydrophobic material  280  advantageously permits any sensor having exposed conductors to which the non-hydrophobic material  280  is attached, including any one or more of the measurement sensor  234 , leak detection and moisture content measurement sensor  270  and the condensation sensor  276 , to provide a measurement result indicative of condensation. 
     In various embodiments, any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), measurement sensor  234  ( FIGS. 18   a  to  18   d ) and leak detection and moisture content measurement sensor  270  ( FIGS. 19   b  and  20   b ) or other similar sensor can be connected to one or more devices such as the data acquisition units  16  ( FIGS. 1 and 2 ) and adhered to a surface, such as a wall, floor, ceiling and/or roof of the building  12  ( FIG. 1 ). For example, a sensor can be laid along the base of a wall to detect fluid leaking down the wall as it arrives at the floor. One or more sensors may be laid in a rectangular grid along a floor, ceiling or roof member. Where a building  12  surface, such as a horizontally disposed floor or ceiling for example, has a corrugated surface or other grooves to direct fluid flow longitudinally, then spaced apart sensors can be laid laterally, including parallel to each other, to detect such longitudinal fluid flow. Where a building  12  surface is sloped such that gravitationally induced fluid flow is likely to occur in a downward direction, then one or more spaced apart sensors can be laid perpendicular to such downward direction to detect such downward fluid flow, possibly in conjunction with a pair of sensors oriented parallel to the downward direction and disposed at opposing ends of such sloped building  12  surface. 
     Additionally or alternatively, any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), measurement sensor  234  ( FIGS. 18   a  to  18   e ) and leak detection and moisture content measurement sensor  270  ( FIGS. 19   b  and  20   b ) or other similar sensor can be connected to one or more devices such as the data acquisition units  16  ( FIGS. 1 and 2 ) and adhered to a surface of a fixture of the building  12  ( FIG. 1 ), such as a plumbing fixture, including possibly a plumbing pipe or other conduit, equipment, including housings of equipment, and other fixtures. In general, the inventive system, apparatus, method and sensors for monitoring structures described or illustrated herein is not limited to building structures and may be suitably used for monitoring other structures such as equipment, infrastructure, and other items where moisture may be of concern. For example, any one or more of the sensors described or illustrated herein may be suitably used for monitoring the condition of a pipe (not shown). In such example, the temperature and external surface moisture of the pipe may be monitored, such as by wrapping a sensor around the pipe and transmitting measurement results to the gateway  18  ( FIG. 1 ) for analysis. Such analysis may include predictive analysis in which the likelihood that the pipe will develop a leak, such as by forming a crack in the material of the pipe due to freezing temperatures, an accumulation of moisture and/or condensation on the surface of the pipe, or any combination thereof, is determined. 
     Any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), measurement sensor  234  ( FIGS. 18   a  to  18   e ) and leak detection and moisture content measurement sensor  270  ( FIGS. 19   b  and  20   b ) or other similar sensor may be suitably used in producing measurement results that can be reported by the system  10  to a user as a moisture content measurement specific to any particular type of material, such as a material having a known moisture transfer characteristic for example, as a moisture level measurement particularly suitable for general materials, such as concrete, gypsum, masonry or other aggregate materials, or any combination thereof for example. 
     Any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), measurement sensor  234  ( FIGS. 18   a  to  18   e ) and leak detection and moisture content measurement sensor  270  ( FIGS. 19   b  and  20   b ) or other similar sensor may be used with or without any one or more of the probe  232 , probe  242 , pair of probes  260 , or any combination thereof. Any one or more of the probe  232 , probe  242 , pair of probes  260  may include a non-isolated probe, in which the entire length thereof is conductive, or an isolated probe in which a specific portion thereof is conductive, thereby permitting the association of a measurement result with a specifiable depth into a material, for example. 
     Any one or more of the encloseable moisture content sensor  214  ( FIG. 15 ), moisture content sensor  224  ( FIGS. 16 and 17 ), measurement sensor  234  ( FIGS. 18   a  to  18   e ) and leak detection and moisture content measurement sensor  270  ( FIGS. 19   b  and  20   b ) may be connected to measurement sensor connector  32  ( FIG. 3 ). For example, the sensor connected to the measurement sensor connector  32  may include a reference impedance, which may be a 20 mega-ohm resistor for example, at the terminal end of such sensor, thereby forming an exemplary terminated circuit which advantageously may be suitable for continuity testing and have improved measurement accuracy and/or an extended measurement range. A reference impedance or reference circuit attached to a sensor connected to the measurement sensor connector  32  may advantageously form a half-bridge circuit in conjunction with the sensor circuitry  42  ( FIG. 3 ). 
     Thus, there is provided a measurement sensor for detecting moisture, which includes: (a) a pair of spaced apart conductors; and (b) an impedance circuit electrically connectable in parallel with said pair of conductors and having a finite impedance such that when said impedance circuit is connected an impedance of said measurement sensor greater than said finite impedance indicates an impaired connection. 
     In accordance with another aspect of the invention, there is thus provided a termination module for a moisture detection measurement sensor, the sensor comprising a pair of spaced apart conductors, the termination module comprising: (a) a base attachable to the sensor; and (b) an impedance circuit supported by said base such that said impedance circuit is electrically connected in parallel with the pair of conductors when said base is attached to the sensor, said impedance circuit having a finite impedance such that when said base is attached to the sensor an impedance of said measurement sensor greater than said finite impedance indicates an impaired connection. 
     In accordance with another aspect of the invention, there is thus provided a moisture content measurement sensor for measuring moisture content of a structural material, the moisture content measurement sensor comprising: (a) a pair of spaced apart conductors enclosed within an electrically insulating material; and (b) a plurality of electrically conductive probe supports, each said probe support being attached to one of said conductors and dimensioned to receive a probe for insertion into the structural material, said each probe support forming an electrical connection between said one conductor and said probe. 
     While embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only. The invention may include variants not described or illustrated herein in detail. For example, although not shown in  FIG. 2  for simplicity of illustration, the data acquisition unit  16  may include in various embodiments additional control lines between the processor  22  and other components of the data acquisition unit  16 , such as the internal temperature sensor  26 , internal pressure sensor  28 , interface circuit  34 , measurement sensor switch  38 , sensor circuit  40 , measurement result switch  64 , wireless transceiver  66 , bus transceiver  48 , bus switch  72 , power mode switch  58  and/or the auxiliary power switch  84 , to facilitate control by the processor  22  of operations of the data acquisition unit  16 . Thus, the embodiments described and illustrated herein should not be considered to limit the invention as construed in accordance with the accompanying claims.