Abstract:
An apparatus and corresponding method measure physical parameters using a plurality of low-cost sensors coupled in series is provided. These sensors can be thermal sensors for measuring the temperature of a heating pad. Different types of sensors to measure temperature, moisture, pressure, or state change of a switch may be employed. Such sensors may be distributed throughout a building to concurrently monitor multiple physical parameters at numerous locations. The sensors are easily manufactured, thus reducing sensor cost. Costs are further reduced by the use of two wires to connect the series of sensors. Moreover, the wires can be run easily through conduit or cable troughs.

Description:
RELATED APPLICATION 
   This application claims the benefit of U.S. Provisional Application No. 60/766,485, filed on Jan. 23, 2006. The entire teachings of the above application are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   Heating pads are normally used to apply heat to parts of the body to aid in healing or for comfort. Most consist of a remote control device and a heating device. The remote control is typically plugged into a household AC power outlet and regulates the temperature of the heating device. The remote control has a user interface, typically pushbuttons or a multi-position switch, so the user can turn the heating device power on or off and select a desired temperature. The heating device consists of a heating means, usually a flexible insulated wire, a means of preventing unsafe temperatures, and a cover to prevent user contact with the electrical components. 
   One method of controlling temperature is to use a thermostat that opens the heating power circuit when a fixed temperature is reached. However, such thermostats can be relatively expensive, costing approximately twenty-two cents each. In addition to heat from the heating wire, an additional source of heat is applied to the thermostat by means of a resistive heating source with a power set by the remote control. A low heat is achieved by passing all of the current that is flowing through the heating wire through the additional heating source, causing the thermostat to open at a lower temperature than it would if it were heated by the heating wire alone. To achieve the highest desired temperature, no power is applied to the resistive source, and for a mid range temperature power is applied to the resistive heating source for one-half cycle of the AC line. 
   Typically a second or third thermostat is used in separate sections of the heating pad to prevent unsafe temperatures from occurring due to uneven heating. Such an unsafe condition can occur when a portion of the pad is covered, preventing heat from radiating. The additional thermostats open the heating wire circuit before an unsafe temperature occurs. In these cases, the temperature is monitored in only limited locations and the measured temperature is not representative of the average temperature of the heating pad. Further, thermostats generate electrical noise when they open and close and are expensive. 
   Another method of controlling temperature is to use a separate sensing wire that is concentrically wound around the heating wire. The resistance of the sensing wire varies with temperature by a known amount. Therefore, by sensing the wire resistance, the temperature can be calculated. The control device constantly monitors the sensing wire resistance and calculates the wire temperature. If the temperature is above the user-selected value, power is removed from the heating wire. If the temperature is below the user-selected value, power is applied to the heating wire. 
   Because the sensing wire is distributed over the entire heating wire, its resistance is a measure of the average temperature of the wire. To prevent localized hot spots from reaching a dangerous temperature, the insulation between the heating and sensing wires is made of a material that melts or becomes electrically conductive when unsafe temperatures are approached. A circuit in the remote control monitors the resistance between the heating and sensing wires and removes power from the heating wire if the resistance falls below a value corresponding to an unsafe temperature. 
   The sensing wire resistance changes are small, typically 0.25% per degree Fahrenheit. The variation in the room temperature resistance of the sensing wire is large enough that an initial calibration must be done on each heating pad, thereby adding manufacturing expense. Further, the pad must be discarded and replaced if localized heating occurs that melts the insulation between the heating and sensing wires. Moreover, the sensing wire does not accurately sense the pad temperature because it is in close proximity to the heating wire, and is separated from the surface of the pad by the outer insulation layer and the pad cover components. 
   SUMMARY OF THE INVENTION 
   An apparatus and corresponding method measure physical parameters using a plurality of low-cost sensors coupled in series. The sensors each have a circuit with a time constant relating to a physical parameter to be measured by the sensors. Each circuit causes measurement signals to be generated in series. Further, a module provides a drive signal to the sensors to generate the respective measurement signals. The module also measures the physical parameters based on a metric associated with the respective measurement signals. 
   The time constant of the circuit may be defined by the characteristics of a transducer or a combination of the transducer and at least one passive circuit element. Further, the time constant may be changed, thereby affecting the metric associated with the respective measurement signal generated by the sensor. Or, the time constant may be selectively changed so that one sensor can measure multiple physical parameters. 
   The sensors include a transducer that may be a temperature transducer to measure temperature, a moisture transducer to measure moisture or humidity, a pressure transducer to measure pressure, or a switch to measure the state change of a switch. The physical parameters may be measured by using a pulse, period between pulses, amplitude, voltage, voltage change, or current. 
   To reduce wiring costs, the series of sensors are electrically coupled with the module via two wires which provide the drive signal. Measurement signals are transmitted between the sensors and module. Three or more wires may also be used. 
   In order to convert the metric to an operational parameter relating to the respective physical parameter, the module must include memory to store conversion data. The module further includes an interface to provide the operational parameter to a system configured to influence the physical parameters to be measured. Such a physical parameter is the temperature of a heating pad. 
   The module includes circuitry coupled to the sensors to generate pulses based on the measurement signals and measures the physical parameters as a function of a time period between adjacent pulses. Moreover, the module includes an interface to interact with a system that influences the physical parameters to be measured. 
   The module provides the drive signal to the sensors by providing the drive signal to a first sensor in the series of sensors, which, in turn, provides a drive signal to a next sensor in the series of sensors, and so forth, except for the last sensor in the series. The sensors generate the measurement signals by affecting the drive signal in a manner that is measurable by the module. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
       FIG. 1A  is an illustration of a user applying a heating pad plugged into a household AC electrical outlet by placing the heating pad on a part of the user that can benefit from heat therapy. 
       FIG. 1B  is an illustration of a heating pad showing the location of a series of ten remote sensors in the heating pad. 
       FIG. 2A  is a block diagram illustrating the heating pad and a remote control. 
       FIG. 2B  is a circuit diagram illustrating the remote control in series with a plurality of temperature sensor elements. 
       FIG. 3  is a flow diagram illustrating a method for measuring physical parameters. 
       FIG. 4  is a flow diagram illustrating a method for controlling the temperature of a heat pad. 
       FIG. 5A-1  is a diagram illustrating a heating pad and controller constructed according to the circuit described in  FIG. 2B  with felt insulation applied to the top and bottom of the heating pad, respectively. 
       FIG. 5A-2  is a diagram illustrating a heating pad and controller constructed according to the circuit described in  FIG. 2B  with felt insulation applied to the bottom of the heating pad and the felt insulation on top of the heating pad removed. 
       FIG. 5B  is a signal diagram illustrating a drive signal and the pulses present on the PULSES input to the controller at an average heating pad surface temperature of 137 degrees Fahrenheit. 
       FIG. 5C  is a table illustrating the time of each pulse, the time difference from the previous pulse, and the calculated temperature of each sensor in the heating pad. 
       FIG. 5D  is a signal diagram illustrating power on duty cycle and average temperature versus time for the testing conditions of the heating pad as illustrated in  FIGS. 5A-1  and  5 A- 2 . 
       FIGS. 6A-6H  are circuit diagrams illustrating alternate sensor configurations that may be employed to measure different physical parameters. 
       FIGS. 7A-7B  are circuit diagrams illustrating a third wire, in addition to the pair of wires, added to the series of sensors, to return pulses to the controller and to provide the reference voltage to comparator, respectively. 
       FIG. 8A  is a circuit diagram illustrating an optional plug-in sensing element consisting of a thermistor and capacitor. 
       FIGS. 8B-8C  are circuit diagrams illustrating configurations similar to that in  FIG. 8A  but with a thermistor or capacitor only in the plug-in sensing element, respectively 
       FIG. 9  is an illustration of a lobby of a building with a series of sensors deployed. 
       FIG. 10  is an illustration of a structure, such as a home, with sensors deployed. 
       FIG. 11  is diagram illustrating a network of multiple sensor systems (not shown) connected to the Internet or other network, such as a wireless network (not shown), to monitor the status of sensors in an office lobby and a home from a remote location where the Internet or other network can be accessed. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A description of example embodiments of the invention follows. Although the present description is given in terms of a heating pad application, it should be understood that the present invention has applications in other areas requiring remote sensing of physical parameters. 
     FIG. 1A  is an illustration of a user  102  applying a heating pad  100  plugged into a household AC electrical outlet  103  by placing the heating pad  100  on a part of the user  102  that can benefit from heat therapy. The user  102  may control the heating pad  100  through a remote control  104 , more generally referred to herein as a module. A module may contain more or fewer components than in a remote control, depending on the functionality required. 
     FIG. 1B  is an illustration of a heating pad  100  showing the location of a series of ten remote sensors  105   1 - 105   10  in the heating pad  100 . The number of sensors  105  in the series of remote sensors  105   1 - 105   n  in a heating pad  100  can vary by design and application. The heating wire  110  is distributed over the heating pad  100  and connected to the remote control (not shown). A pair of wires  115  carries signals to and from the series of remote sensors  105   1 - 105   10  and is also connected to the remote control (not shown). 
     FIG. 2A  is a block diagram of the heating pad  100  and a remote control  104 . A source of power  205 , typically AC power from a household outlet ( 103  in  FIG. 1A ), is connected to the remote control  104  and provides power to the heating wire  110  and, through a power supply  210 , to the remote control circuitry  215 . A microprocessor or application specific integrated circuit (ASIC)  220  controls power to the heating pad  100  by turning a triac  225  on and off and sends a interrogation signal to and receives signals representing each sensor&#39;s  105  temperature from the heating pad temperature sensors  105   1 - 105   n . A termination  230  provides a load to the last sensor  105   n  similar to the load provided to the other sensors  105   1 - 105   n-1 . 
     FIG. 2B  is a circuit diagram illustrating the remote control in series with a plurality of temperature sensor elements. A source of AC power (not shown) ( 205  in  FIG. 2A ) is connected to the remote control  104  through J 1 . A power supply (not shown) provides DC power to the remote control circuitry  215 . Means of selecting temperature and turning the heating pad on and off are also not shown. Periodically, the controller  220  in the remote control  104  applies a voltage to the first sensor  105   1  in the heating pad  100  through resistor R 9  by pulling the READ line to ground, turning on PNP transistor Q 3  whose emitter is connected to a source of DC voltage. This applies a reference voltage to the positive input of comparator U 1  by means of a resistive voltage divider comprised of R 2  and R 3 . The voltage from the controller is also applied to thermistor RT 1  and begins charging capacitor C 1  connected to the negative input of comparator U 1 . When the voltage on the negative input exceeds the voltage on the positive input, the output of U 1  will be pulled to ground turning on PNP transistor Q 1 . Q 1  collector supplies voltage to the next sensor  105   2  and through capacitor C 2 , a positive pulse to the negative input of U 1  to insure a rapid turn on of U 1  and Q 1 . Because C 1  resists a rapid change in voltage, R 4  is needed to allow the positive feedback effect of the pulse through C 2  to induce rapid turn on of the voltage to the next sensor. 
   Capacitor C 1  charges at a rate given by:
 
 V   C1   =V   in (1 −e   T/RthC )
 
   Where:
         V in  is the voltage applied from the remote control   V C1  is the voltage across C 1     R th  is the resistance of thermistor RT 1     C is the capacitance of C 1     T is time since voltage was applied       

   Solving for time T:
 
 T=R   th   C ln(1− V   C1   /V   in )
 
   Comparator U 1  begins switching on when Vc 1  exceeds the positive input voltage V th .
 
 V   th   /V   in   =R 3/( R 2 +R 3)
 
   Because V th  is substantially equal to V C1 :
 
 T=R   th   C ln(1− V   th   /V   in ) and
 
 T=R   th   C ln(1− R 3/( R 2+ R 3))
 
   Except for a slight error caused by comparator U 1  offset voltage, the delay from application of voltage Vin to the application of voltage to the subsequent sensor  105  is proportional to R th  and independent of the sensor&#39;s input voltage. The voltage applied to subsequent sensors  105  decreases as the voltage drop across R 9  increases due to increased current as more sensors  105  are switched on but the error in switching time is small. 
   As each sensor  105  is switched, a rapid increase in current through R 9  occurs. Resistor R 6  on the output of the last sensor  105   n  provides a termination R 6  ( 230  of  FIG. 2A ) so the current increase when the last sensor  105   n  is switched on is substantially equal to the other sensors  105   1 - 105   n-1 . Capacitor C 4 , resistor R 14 , transistor Q 4  and resistor R 10  respond the rapid change in current to produce a pulse at the PULSES input to the controller  220 . 
     FIG. 3  is a flow diagram  300  illustrating a method for measuring physical parameters. After starting  305 , a drive signal is applied  310  to a series of remote sensors  105   1 - 105   n . Each sensor  105  in the series of remote sensors  105   1 - 105   n  generates a measurement signal  315  relating to a physical parameter. The measurement signal is then processed  320  to determine the value of the physical parameter. After a delay  325 , the process repeats, starting with the application of the drive signal  310 . 
     FIG. 4  is a detailed flow diagram  400  illustrating a method for controlling the temperature of a heating pad  100 . The process starts  405  when the user  102  turns on the heating pad  100  and selects a desired temperature. The controller  220  then applies a voltage  410  to the first sensor  105   1  in the series of sensors  105   1 - 105   n  and sets a timer to zero  415 . The value of the timer is then checked  420  to insure a pulse has been received within a maximum time limit. Because the timer has just been set to zero  415 , the answer is no  423 . 
   The controller  220  then checks  425  for the presence of a pulse and, if one has not occurred  427 , returns to check if the timer is at the maximum limit  420 . If there are no faults in the series of sensors  105   1 - 105   n , a pulse eventually will be found  428 . The value of the time will be read  430 . The time difference between the last pulse will be converted to a temperature value  435 . The controller  220  then determines if the temperature is too hot  440 . If the temperature is too hot  443 , power is turned off  460  so that the heating pad  100  may cool. If the temperature is not too hot  442  (below a safe limit), the controller  220  checks  445  if this pulse was from the last sensor  105   n . If not  447 , the controller  220  returns to check the timer limit  420  and wait  425  for the next pulse. If the last pulse was received  448 , the controller  220  converts  450  the time of the last pulse to determine the average sensor temperature. 
   The controller  220  then determines if the average temperature is too hot  455 . If the average temperature is above  458  the user selected temperature (too hot), power to the heating pad  100  is turned off  460 . If it is below  457  the user selected value, power to the heating pad  100  is turned on  465 . In either case, the controller  220  delays  470  for a time sufficient to discharge the capacitors in the series of sensors  105   1 - 105   n  and returns to apply  410  voltage to the first sensor  105   1  for the next measurement. 
   If all of the pulses are not received in an interval that is less than the maximum time all pulses should occur in a properly operating system, the “Timer at Limit?”  420  is answered yes  422 , power is removed  475  from the heating pad  100 , and a light emitting diode (LED) or other indicating device flashes  480  rapidly to indicate a catastrophic failure. No further operation is possible until power is removed causing the controller  220  to reset  485 . 
   If the controller  220  is reset  488 , the controller  220  returns to apply  410  voltage to the first sensor  105   1  for the next measurement. If the controller  220  is not reset  487 , the LED or other indicating device, continues to flash  480  indefinitely or until the main AC power source  103  is disconnected from the controller  220 . 
     FIG. 5A-1  is a diagram illustrating a heating pad  100  and controller  220  (not shown) constructed according to the circuit described in  FIG. 2B  with felt insulation  500 ,  505  applied to the top and bottom of the heating pad  100 , respectively. The heating pad  100  was tested by insulating it between two layers of one inch thick felt  500 ,  505 . Temperatures of the heating pad  100  were measured with an array of 5 thermocouples  510  mounted on one inch square copper plates  515  centered across the short axis of the heating pad  100  at the center of the long axis between the bottom felt insulation  505  and the heating pad  100 . An aluminum plate  502  was placed on the top felt insulation  500  to ensure the bottom piece of felt insulation  505 , thermocouples  510 , heating pad  100  and top felt insulation  500  were held together. Measurements were taken for twenty minutes while the heating pad  100  was insulated between the layers of felt  500 ,  505 . 
     FIG. 5A-2  is a diagram illustrating a heating pad  100  and controller  220  (not shown) constructed according to the circuit described in  FIG. 2B  with felt insulation  505  applied to the bottom of the heating pad  100 , and the top felt insulation  500  and aluminum plate  502  removed. After twenty minutes, the top felt insulation  500  and aluminum plate  502  were removed, exposing the top of the heating pad  100  to ambient air, as illustrated in  FIG. 5A-2 . The heating pad  100  then continued to operate until the end of testing when power was turned off. 
     FIG. 5B  is a signal diagram illustrating a drive signal  520  and the pulses  525  present on the PULSES input to the controller  220  at an average heating pad surface temperature of 137 degrees Fahrenheit. Each pulse  525   1 - 525   10  is generated by its respective sensor  105  in the series of sensors  105   1 - 105   10  illustrated in  FIG. 1B . The controller  220  measures the time difference  530  between adjacent pulses  525  and calculates the temperature of each sensor  105 . The time to the last pulse  525   10  is a measure of the average temperature of each sensor  105   1 - 105   n  and is compared to the desired temperature selected by the user  102 . 
   If the average temperature is below the desired temperature, Triac Q 5  is turned on to apply power to the heating wire  110 . If the temperature is above the desired value, triac Q 5  turns off power to the heating wire  110 . Because the controller “knows” the temperature of each sensor  105   1 - 105   n , power is also turned off if the temperature of any sensor  105  exceeds a safe value. If a break in the sensor wiring  115  occurs, or a sensor  105  fails to respond in a reasonable time, temperature cannot be measured accurately and power is also removed from the heating wire  110  to prevent an unsafe overheating condition. 
   After receiving the last pulse  525 , the controller  220  delays for a time to allow capacitors C 1  and C 2  to discharge. Then the process repeats. 
     FIG. 5C  is a table illustrating the time of each pulse  525 , the time difference  530  from the previous pulse  525 , and the calculated temperature of each sensor in the heating pad. 
     FIG. 5D  is a signal diagram illustrating power on duty cycle and average temperature versus time for the testing conditions of the heating pad as illustrated in  FIGS. 5A-1  and  5 A- 2 . First, as in  FIG. 5A-1 , the temperature of the heating pad  100  was allowed to stabilize. Then, from zero to twenty minutes, readings of the five thermocouple  510  temperatures were averaged and plotted as a function of time. Temperature is shown in the upper curve  540  and the state of heating wire current in the lower curve  545 . 
   At twenty minutes, the top layer of felt was removed, as in  FIG. 5A-2 . Note the increase in the “on” time of the heating wire current needed, during each measurement cycle, to maintain the temperature of the heating pad  100  as more heat is radiated into the ambient air. This test demonstrates that an average heating temperature was maintained with only a small error when the amount of heat lost from the heating pad  100  changed. The average temperature of the surface of the heating pad  100 , as measured by the array of thermocouples  510  and plotted in  FIG. 5D , is lower than the average temperature of the sensors, as provided in  FIG. 5D , due to the thermal drop across the material surrounding the heating wire. 
     FIGS. 6A-6H  are circuit diagrams illustrating alternate sensor configurations that may be employed to measure different physical parameters. 
     FIG. 6A  is a circuit diagram illustrating a sensor that responds to temperature in the manner previously described. 
     FIG. 6B  is a circuit diagram illustrating a lower-cost circuit in which the comparator U 1  has been replaced by NPN transistor Q 2 . Operation is similar to the comparator except that the base to emitter voltage of the transistor must be overcome before transistor Q 2  turns on. If the supply voltage is large compared to the base emitter drop, the error is acceptable. 
   Other embodiments of the invention can be used to measure physical parameters in applications other than heating pads. 
     FIG. 6C  is a circuit diagram illustrating an inductor L 1  in place of the thermistor RT 1  and a resistor R 1  in place of the capacitor C 1  of  FIG. 6B . When voltage is applied to the sensor  105 , current through the inductor L 1  will increase with time at a rate depending on the inductance value. As inductor current increases, the voltage drop across resistor R 1  increases until comparator U 1  turns on. A core inside the coil L 1  could be attached to a movable object so the position of the movable object varies the position of the core and therefore the value of the inductance. The delay between application of sensor voltage and the pulse created when comparator U 1  turns on would then be a measure of the position of the movable object. 
     FIG. 6D  is a circuit diagram illustrating a method of using the invention to determine the value of a DC voltage. Time to switch on the comparator U 1  is determined by the time taken to charge capacitor C 1 , through R 1  to the value of the DC voltage. An AC voltage could also be measured by first rectifying and filtering it to generate a DC voltage. 
     FIG. 6E  is a circuit diagram illustrating a sensor that can be used to measure relative humidity. The capacitance is related to relative humidity in a known way so that the time to charge the capacitor HS 1  and switch on comparator U 1  can be use to measure humidity. Another type of humidity sensor varies resistance in response to relative humidity and could be used in the circuit of  FIG. 6A  by replacing RT 1  with a resistive humidity sensor. 
     FIG. 6F  is a circuit diagram illustrating a cadmium sulphide light sensor CDS 1  in place of the thermistor RT 1  in the circuit of  FIG. 4A . Because the value of light sensor resistance is related to the light level in a known way, the time delay of the pulse produced can be used to measure light level. 
     FIG. 6G  is a circuit diagram illustrating a circuit used to determine the state of a switch S 1 . In one application, the switch S 1  could be attached to a door so an alarm is sounded when the door is opened. When the switch S 1  is open capacitor C 1  is charged through R 1  producing a pulse of a known delay. When the switch S 1  is closed, resistor R 6  is connected in parallel with R 1  and a shorter delay is produced. 
     FIG. 6H  is a circuit diagram illustrating replacing resistor R 1  with a rheostat R 9 . The value of the rheostat R 9  can be varied by a physical connection to a movable object. For example, a rheostat with a rotating shaft could be attached to a float to determine the level of a liquid. 
     FIG. 7A  is a circuit diagram illustrating a third wire  717 , in addition to the pair of wires  115 , added to the series of sensors  105   1 - 105   n , to return pulses to the controller  220 . The resistor R 9  of  FIG. 2B  in series with the sensor drive is eliminated so the voltage applied to subsequent sensors  105  is increased, allowing more sensors  105  to be connected in the series of sensors  105   1 - 105   n  before the sensor input voltage drops to an unacceptable level. Without the series resistor R 9 , the main source of voltage drop is the saturation voltage of PNP transistor Q 2 . 
     FIG. 7B  is a circuit diagram illustrating a third wire  717 , in addition to the pair of wires  115 , added to the series of sensors  105   1 - 105   n  to provide the reference voltage to comparator U 1 . A single precision reference voltage could be generated in the remote control  104 . Because the sensor does not compensate for changes in input voltage, increased complexity would be required in the controller  220  to adjust the calculated temperature as a function of the location of the sensor  105  in the series of sensors  105   1 - 105   n . Sensors  105  further from the controller  220  would have a lower input voltage due to an increased drop across resistor R 9  and a longer pulse interval. 
     FIG. 8A  is a circuit diagram illustrating an optional plug-in sensing element  800   a  consisting of a thermistor RT 1  and capacitor C 1 . Using this approach, different types of sensing elements  800  could be plugged into a common sensor circuit  805  so a series of sensors  105   1 - 105   n  could be installed and the parameter sensed at each sensor  105  changed by simply changing the plug-in sensing element  800 . 
     FIGS. 8B and 8C  are circuit diagrams illustrating configurations similar to that in  FIG. 8A  but with a thermistor RT 1  or capacitor C 1  only in the plug-in sensing element  800   b ,  800   c , respectively. 
     FIG. 9  is an illustration of a lobby  900  of a building with a series of sensors  105   1 - 105   n  deployed. Different types of sensors, such as those illustrated by  FIGS. 6A to 6H , may be used in combination in a series of sensors. The sensors measure the status of the entrance doors  905 , room temperature  910 , humidity  915 , light  920 , a switch  925 , and battery voltage  930 . However, the controller or module must know what type of sensor is located at each position in the series of sensors so that the difference between pulses may be converted to the metric appropriate for that sensor. The difference between pulses (or other metric associated with the respective measurement signals) based on the type of sensor being employed. Further, the module (not shown) that processes the measurement signals knows the expected timing (or other meaning) to sense an alarm or other condition associated with any one of or multiple sensors. 
     FIG. 10  is an illustration of a structure, such as a home  1000 , with sensors deployed. One application  1005  can be to use sensors  105  to measure temperature at selected locations, such as an attic, to detect a fire. Another application  1010  can to use sensors  105  to measure the temperature in each room so the airflow from the heating or air conditioning could be directed where it is needed. Further applications can be to place additional sensors  105  in a basement  1015  or inside walls  1010  or in an attic  1005  to measure humidity and to provide an early indication of a potential for mold growth to protect the value of a home. 
     FIG. 11  is diagram illustrating a network of multiple sensor systems (not shown) connected to the Internet  1100  or other network, such as a wireless network (not shown), to monitor the status of sensors  105  in an office lobby  900  and a home  1000  from a remote location  1105  where the Internet  1100  or other network can be accessed. In this example network environment, data communications, such as communications packets, can be employed to provide raw data (e.g., periods between pulses) or summary data (e.g., fault condition detected) from the sensor systems to a server (not shown) at the remote location  1105  configured to support the sensor systems. 
   Service models may be subscription-based and may include monitoring, diagnostics via two-way communications, repair, testing, etc. The communications may include any sort of diagnostic request known in the art, with an appropriate response sent in reply. Further, powerline communications may be employed to remotely turn off a heating pad left on for too long a period or left unattended at the initiation of a user or automatically initiated by a remote server as determiner by reported statistics sent by the heating pad. Moreover, email messages may be sent informing the owner of faults in the heating pad or the necessity of repair or replacement. 
   While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.