Patent Publication Number: US-2013245965-A1

Title: Handheld HVAC/R Test and Measurement Instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 13/072,636 filed on Mar. 25, 2011, and claims the benefit of U.S. provisional application Ser. No. 61/768,546 filed on Feb. 25, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention involves servicing and testing equipment used in the heating, ventilating, air conditioning, and refrigeration (HVAC/R) field and, more particularly to handheld test and measurement devices useful for HVAC/R technicians for the performance of their vocation. 
     HVAC/R (or, sometimes referred to simply as HVAC) technicians employ a wide variety of servicing and testing equipment in the daily and routine performance of their vocation. Some of the electrical measuring and test instruments include: voltmeters to measure electric potential differences (volts, V; volts AC, VAC; volts DC, VDC); ohmmeters to measure electric resistance (ohms, S 2 ); ammeters to measure electric current (amperes, A; alternating current, AC; direct current, DC); capacitance meters to measure electric capacitance (farads); thermocouples to measure temperature (degrees F.); wattmeters to measure electric power (Watts, W); and data logging instruments to capture and store measurement data over time. 
     Exemplary refrigerant system servicing and testing equipment include: various types of thermometers—dial thermometers, digital thermometers, thermocouples, infrared thermometers; gage manifold sets for measuring operating pressures (kilopascals, kPa; pounds per square inch, psi) in one of three ways—atmospheric (psi), gage (psig), or absolute (psia) pressure—and for adding or removing refrigerant; superheat and subcool meters that measure low side (suction line) pressure and temperature (for determining superheat) and high side (condenser discharge line) pressure and temperature (for determining subcool); psychrometers for measuring wet bulb and dry bulb temperatures to determine relative humidity; and leak detectors such as electronic leak detectors or ultrasonic-type leak detectors for detecting refrigerant leaks. 
     Heating system servicing and testing equipment may include: draft gages for measuring the amount of draft in inches of water column in the flue pipe opening and in the furnace inspection port (to compare flue draft with manufacturer specifications and to detect leaks); flue gas analyzers for measuring carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), nitrous oxide (NO), and flue pressure; refrigerant and gas identifiers and monitors; and oxygen-depletion alarms for warning technicians of dangerous conditions in enclosed or confined equipment areas. 
     Pressure measuring devices include: manometers for measuring small pressures (under one inch water column); and Bourdon tube gages for measuring higher pressures in psig. 
     Air speed and air volume measuring devices such as rotating vane anemometers, thermal anemometers, and flow hoods are used for measuring air speed (feet per minute, fpm) and air volume (cubic feet per minute, CFM). 
     Indoor air quality (IAQ) test and measurement devices may include particle counters, infrared cameras, thermal imagers, and various pollutant sampling kits, devices, and sensors—for detecting mold, lead, asbestos, radon, CO, nitrogen dioxide (NO2), mercury, volatile organic compounds (VOC&#39;s) such as ketones and hydrocarbons, and ozone (O3)—in addition to instruments to measure CO2 percentage, temperature, and relative humidity percentage. 
     Numerous techniques are used by HVAC/R technicians to service a wide variety of different types of systems, requiring the technician to acquire, learn to use, and maintain several separate servicing and testing devices as well as accompanying technical reference materials such as refrigerant pressure-temperature charts and calculation algorithms and methods. HVAC/R test and measurement instruments are needed that reduce the number of separate instruments and technical reference materials needed to install and service HVAC/R systems. HVAC/R test and measurement instruments are needed that incorporate greater flexibility, versatility, portability, and functionality than those which are presently available. 
     What is needed, therefore, are improved techniques and devices designed to help HVAC/R technicians in their vocation by reducing the number and complexity of devices, systems, and technical materials needed to perform various servicing and testing procedures. A handheld sized device or family of related, interconnectable, or multi-purpose devices that may be used for a wide variety of HVAC/R system servicing and testing applications, and that provide the technician with real-time system performance information, guidance in system analysis and troubleshooting, is needed. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL DRAWINGS 
       For a more complete understanding of the present invention, the drawings herein illustrate examples of the invention. The drawings, however, do not limit the scope of the invention. Similar references in the drawings indicate similar elements. 
         FIG. 1  illustrates an exemplary air conditioning and refrigeration system with a handheld HVAC/R test and measurement instrument, according to one embodiment. 
         FIG. 2  illustrates various embodiments of the handheld HVAC/R instrument shown in  FIG. 1  connected with sensor module inputs and external output and peripheral devices. 
         FIG. 3  illustrates various embodiments of inputs connectable to a handheld HVAC/R instrument as in  FIGS. 1 and 2 . 
         FIG. 4  illustrates optional sensor kits for use with a handheld HVAC/R instrument as in  FIGS. 1-3 , according to various embodiments. 
         FIG. 5  depicts a partial, generalized operational flow chart of a handheld HVAC/R instrument and sensor kit, according to various embodiments. 
         FIG. 6  shows an exemplary functional block diagram of a handheld HVAC/R instrument as in  FIGS. 1-3 , according to various embodiments. 
         FIG. 7  illustrates various embodiments of a handheld sized test and measurement data interface unit for receiving sensor inputs from sensor kits and providing received sensor input information to a handheld sized user interface. 
         FIG. 8  shows an exemplary functional block diagram of a handheld sized data interface unit as in  FIG. 7 , according to various embodiments. 
         FIG. 9  illustrates various embodiments of a handheld-sized test and measurement instrument with one or more associated sensor head attachments and multiple wired and wireless communicating configurations. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the preferred embodiments. However, those skilled in the art will understand that the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternate embodiments. In other instances, well known methods, procedures, components, and systems have not been described in detail. 
     Rather than use several different test and measurement instruments when servicing a system such as that shown in  FIG. 1 , the present inventors invented a handheld central or main field test and measurement instrument that is capable of receiving inputs from sensors or sensor modules to perform typical tests and measurements associated with installation and maintenance of HVAC/R systems.  FIG. 1  shows an example air conditioning and refrigeration system  100  with a handheld central or main field test and measurement instrument (hereinafter, “main unit”)  120 , according to one embodiment. The main unit  120  comprises: a handheld-sized instrument with means for receiving a plurality of (ex. 1 through n) inputs  122  via physically wired connections to sensors or sensor modules, via wireless communications with sensor or sender units or sensor modules, or via a combination of the two; means for sending/transmitting a plurality of (ex. 1 through m) outputs  124  via wireless and/or wired connections with various external output devices; a display  126 ; and control buttons  128  and/or up, down, right, left, scroll, and select navigation controls  130 . 
     The exemplary HVAC/R system  100 , or system under test, shown in  FIG. 1  may be any of a wide variety of systems, such systems being described and illustrated more thoroughly in HVAC/R systems treatises, for example the Air-Conditioning, Heating, and Refrigeration Institute&#39;s published reference text, Fundamentals of HVAC/R, by Carter Stanfield and David Skaves, copyright 2010, Prentice Hall, which is incorporated herein by reference. The system  100  shown in  FIG. 1  is presented as a typical HVAC/R system under test, having a compressor  102 , a condenser  106 , a metering device  112 , and an evaporator  114 . Refrigerant (and some lubricating oil) generally flows through piping, as indicated in  FIG. 1 , in a clockwise direction from the compressor  102 , through the condenser  106 , through a metering device  112  (which may, for instance, be a capillary tube type structure or a thermal expansion valve (TEV) device), through an evaporator  114 , and back to the compressor  102 . Not all components are shown. For example, an oil separator may be positioned immediately after (i.e. downstream from) the compressor  102  along hot gas line  104  with an oil return line from the oil separator back to the compressor; a receiver may be positioned after the condenser  106  between the condensate line  108  and the liquid line  110  leading to (i.e. upstream from) the metering device  112 ; and an accumulator may be positioned along the suction (vapor) line  116  after the evaporator  114  and before the compressor  102 . 
     Generally, the compressor  102  and metering device  112  delineate a low side (or low pressure side)  132  and a high side (or high pressure side)  134  of the HVAC/R system  100 , with the compressor  102  causing refrigerant to flow from the low side  132  to the high side  134  in response to operational controls and safeties  118  associated with the compressor via electrical control lines  160 . The compressor  102  delivers pressurized refrigerant to the hot gas line  104  and condenser  106 . As refrigerant flows through the condenser  106 , it transitions from a vapor phase  136  where only vapor is in the lines, to a liquid plus vapor phase  138  within the condenser  102 , and finally to a liquid only phase  140 . Outside ambient air  142  flows into the condenser coils of the condenser  106 , receives heat from the high pressure refrigerant as the refrigerant condenses from a vapor to a liquid, and leaves the condenser coils as (heated) discharge air  144 . 
     Refrigerant flows from liquid line  110  through metering device  112 , through which the line pressure drops from high pressure before the metering device  112  to low pressure following the metering device  112 . The low pressure refrigerant then flows in a liquid phase  140  into the evaporator  114 , transitions into a vapor plus liquid phase  138  as the refrigerant absorbs heat from return air  146  flowing through the evaporator coils (thereby cooling the intake/return air  146  to provide cooled supply air  148 ) and finally transitions into a vapor phase  136 , leaving the evaporator  114  through suction (vapor) line  116 . The low pressure suction (vapor) line  116  refrigerant then flows into the compressor  102  to complete (and repeat/restart) the cycle of refrigerant flow through the HVAC/R system  100 . 
     Low and high side test and measurement points are shown in  FIG. 1 . For example, the temperature of the low side or suction line near (just before) the compressor  102  may be measured at temperature measuring point  150 . The temperature of the suction line (at  150 ) along with the pressure measurement at the suction line port  152  near (just before) the compressor  102  is typically used to check system superheat. Superheat may be defined as (suction line temperature) minus (evaporator saturation temperature). Suction line temperature is typically measured, and evaporator saturation temperature is approximated using measured suction line pressure and pressure-temperature charts (or look-up tables) for the particular type of refrigerant used in the system under test. 
     The temperature of the high side or condensate line leaving the condenser  102  may be measured at temperature measuring point  154 . The temperature of the condensate line (at  154 ) along with the pressure measurement at the condensate line port  156  near (just after) the compressor  102  are typically used to check system subcool. Subcool may be defined as (condenser saturation temperature) minus (condensate line temperature). Condensate line temperature is typically measured, and condenser saturation temperature is approximated using measured condensate line pressure and pressure-temperature charts (or look-up tables) for the particular type of refrigerant used in the system under test. 
     Methods for charging HVAC/R systems for proper superheat and subcooling are well established but vary in application according to the particular type of system (and refrigerant) and require reference to manufacturer specifications, charts, graphs, or other data. Measuring the operating superheat of a thermal expansion valve (TEV) type metering device  112  to, for example, adjust the TEV, typically involves measuring suction (vapor) line temperature and pressure at the expansion valve bulb  158 , since this is where the TEV senses the suction line temperature in its operation and function to maintain a constant system superheat. A TEV type metering device  112  typically includes a thermostatic expansion valve bulb  158  with capillary tube back to the power head of the TEV metering device  112  or a thermistor at  158  electrically connected with the TEV metering device  112  if an electronically controlled TEV metering device  112  is used. Once the TEV is adjusted for the desired superheat (for example, to maintain a superheat of 8-12 degrees F.), proper charging of the system  100  having a TEV type metering device  112  may be checked by measuring system subcool (by measuring condensate line pressure at  156  and condensate line temperature at  154 ) and using a subcooling charging chart (i.e. look-up table) which specifies a desired subcooling corresponding to measured outdoor ambient air temperature and measured indoor wet bulb temperature (or calculated indoor wet bulb temperature using measured relative humidity). If the measured subcooling is less than specified by the charging chart, then the system is undercharged refrigerant should be added. If the measured subcooling is greater than specified, then the system is overcharged and the excess refrigerant should be recovered. 
     For systems having a fixed restriction type metering device  112  (such as a capillary tube type metering device  112 ), proper charging of the system may be checked by measuring system superheat (by measuring suction line pressure at  152  and suction line temperature at  150 ) and using a superheat charging chart which specifies a desired superheat corresponding to measured outdoor ambient air temperature and measured indoor wet bulb temperature (or calculated indoor wet bulb temperature using measured return air temperature and relative humidity). If the measured superheat is more than specified by the manufacturer&#39;s charging chart, then the system is undercharged and refrigerant should be added. If the measured superheat is less than specified, then the system is overcharged and the excess refrigerant should be recovered. 
     Another method, sometimes referred to as the Liquid-Ambient method, for determining whether a system is over or undercharged is to measure the condensate line (or liquid line) temperature at  154  and subtract the measured outdoor ambient temperature at  142 . The difference is then compared with the manufacturer&#39;s specifications. If the difference is more than specified, then the system is undercharged. If the difference is less than specified, then the system is overcharged. 
     In various embodiments, the main unit  120  may be connected, as shown in  FIG. 2 , as a system  200  with its 1 through n inputs  122  comprising wired or wireless communication between sensor sender units (or sender modules)  204  and the main unit  120 , and with its 1 through m outputs  124  comprising wired or wireless communication between the main unit  120  and various external output and peripheral devices  206 ,  208 ,  210 . Exemplary external output and peripheral devices may include any of a wide variety of devices, such as IR printer or other printing devices  206 , laptop or other computing device connected with the main unit  120  via IR, USB, or other means, and/or smartphone or PDA devices communicating with the main unit  120  via Bluetooth, mini USB, or other means. Each of the sender units  204 , as shown, receive sensor inputs  202  from sensors suitably applied to a system under test such as the system  100  in  FIG. 1 , and communicate, preferably in real-time, the sensor input information to the main unit  120 , which in turn preferably monitors in real-time and receives the transmitted sensor input information. 
     The sender units  212 ,  214 ,  216 ,  218  may, for example, comprise sender units with circuitry adapted for particular types or groupings of sensor inputs  202 . The sender unit  212  may, for example, be adapted for location outside at the condenser  106  for measuring system subcool. For example, such a sender unit  212  may be connected to a pressure sensor via connection  220  and a temperature sensor via connection  222  for receiving, respectively, signal information representing high side pressure at condensate line pressure port  156  and signal information representing high side temperature at the condensate line temperature measuring point  154 . In similar fashion, the sender unit  214  may be adapted for location outside at the compressor  102  for measuring superheat, with connections to a pressure sensor via connection  224  and a temperature sensor via connection  226  for receiving, respectively, signal information representing low side (suction line) pressure at  152  and signal information representing low side temperature at the low side temperature measuring point  150 . 
     The sender unit  216  may be adapted for location inside at the evaporator  114  duct work for taking return air  146  temperature and relative humidity measurements, with connections to a temperature sensor via connection  228  and a humidity sensor via connection  230  for receiving, respectively, signal information representing return air  146  temperature and signal information representing return air  146  humidity. 
     The sender unit  218  may be adapted for location outside at the condenser  106  for taking outside ambient air  142  temperature, with connection to a temperature sensor via connection  232  for receiving signal information representing outside ambient air  142  temperature, to, for example, use the Liquid-Ambient method for checking system refrigerant charge. In such application the sender  218  may also be adapted for taking condensate line (or liquid line) temperature at  154 , with connection to a temperature sensor via connection  234  for receiving signal information representing condensate (liquid) line temperature at  154 . Configuring a sender with both temperature sensing inputs needed for use of the Liquid-Ambient method of charging allows for calibration within the sender or main unit  120  of the two temperature sensors to permit more accurate measurement of the temperature difference between the (higher) liquid line temperature and the (lower) outside ambient air temperature, since calibration differences between the two sensors (if two different temperature sensors are used instead of separate measurements using a single sensor) would likely adversely influence system charging. 
     The sender unit  218  may be adapted instead for location inside at the evaporator  114  for taking temperature and pressure measurements near the TEV bulb  158 . In such an application, the sender unit  218  may have connection to a temperature sensor via connection  232  and a pressure sensor via connection  234  for receiving, respectively, signal information representing suction line temperature at  158  and signal information representing suction line pressure at  158 . 
     Instead of configuring the sender units  212 ,  214 ,  216 ,  218  as above, i.e. having sensor inputs grouped according to typical application needs such as (one sender configured for) measuring high side pressure and temperature for measuring superheat, the sender units may be configured to support particular types of sensor inputs. For example, sender unit  212  may be adapted for taking refrigerant line temperatures, with connections to temperature sensors via connections  220  and  222  for receiving signal information representing refrigerant line temperatures, and sender  214  may be adapted for taking refrigerant line pressures, with connections to pressure sensors via connections  224  and  226  for receiving signal information representing refrigerant line pressures. 
     Preferably, each of the sender units  204  include circuitry adapted to permit wireless transmission of sensor information characterizing sensor inputs  202  for wireless reception by circuitry incorporated in the main unit  120  for wirelessly receiving the sensor information from the sender units  204 . In other embodiments, the sender units  204  may include sender units with such wireless transmitting means and/or sender units requiring physically wired communication with the main unit  120 . 
     In still other embodiments, the main unit  120  may not include circuitry adapted to wirelessly receive sensor input information directly. As shown in  FIG. 3 , some sensors and sender units  302  may be in wireless communication with the main unit  120  via wireless transceivers  306 ,  308 , and other sensors and sensor modules  304  may be in directly wired communication with the main unit  120 . For example, sender units  212 ,  214  as previously described may be located outside at the compressor  102  and condenser  106  and communicate wirelessly to wireless transceivers  306 ,  308  via wireless channels  310 ,  312 . The transceivers  306 ,  308  in turn provide the main unit  120  with sensor information via wired inputs  122 . Other sensors  320 ,  322 ,  324  may be located inside at the evaporator and return air duct work and communicate directly via respective wired connections  314 ,  316 ,  318  to the inputs  122  of the main unit  120 . 
     In one embodiment, sensor and sender units  302  comprise wireless sender units  212 ,  214  as previously described for providing sensor input information needed for checking superheat and subcool. The wireless transceivers  306 ,  308  enable the main unit  120  to receive sensor information from the sender units  212 ,  214  wirelessly so that the main unit  120  may be located remotely from the compressor  102  and condenser  106  of the system under test  100 . Sensor and sensor modules  304  include a temperature probe or temperature probe module  320  adapted for receiving signal information representing return air  146  temperature; a humidity sensor or humidity sensing module  322  adapted for receiving signal information representing return air  146  humidity; and a temperature probe or temperature probe  324  adapted for receiving signal information representing suction line temperature at the TEV bulb  158 . In one embodiment, the temperature probe modules  320  and  322  together (shown as  326  in  FIG. 3 ) provide the functionality of sender unit  216  and the temperature/humidity probe  228 / 230  shown in  FIG. 2 . In one embodiment, the temperature probe module  324  (shown as  328  in  FIG. 3 ) provides the functionality of sender unit  218  insofar as the temperature sensor  232  shown in  FIG. 2 . 
     As shown in  FIG. 4 , the handheld HVAC/R test and measurement instrument  120  may be combined with a range of optional sensor/module kits  402 ,  404 ,  406 ,  408 ,  412 ,  414  as a complete HVAC/R test and measurement system  400 , according to various embodiments. In one embodiment, a technician may use the central, main unit  120  with one or more of the optional sensor kits depending upon the application. Other sensor kits may be used, and the kits described are exemplary of typical HVAC/R test and measurement applications and may include different sensors, sender units, probes, or modules than those shown and described. Each kit preferably includes the appropriate probes, sensor attachments, wiring leads, cabling, sensor signal senders/transmitters, transceivers/receivers (if needed) for attachment to the main unit  120 , and other equipment and circuitry for physically taking the desired system measurement (i.e. suction line pressure) and providing sensed measurement signal information (referred to as sensor inputs) receivable by the main unit  120  sensor inputs  122 . 
     The AC kit  402  includes the sensors, sender units, probes, or modules needed to provide the main unit  120  with sensor input information for measuring outdoor ambient temperature, indoor return air temperature, indoor relative humidity, and either the low side (suction line) temperature and pressure needed for measuring superheat or the high side (discharge/condensate/liquid line) temperature and pressure needed for measuring subcool. In one embodiment, AC kit  402  includes a pressure sensor  416  and temperature sensor  418  for measuring pressure and temperature, respectively, of typical refrigerant lines in HVAC/R systems such as system  100  in  FIG. 1 . The pressure and temperature sensors  416 ,  418  are preferably equipped with Schrader or other standard refrigerant line pressure test port fittings, pipe engaging sensor clamps for quality transducer contact for measuring refrigerant (line) temperature, adequate wire/cable lengths, and other features for convenient measurement of superheat and subcool (an similar measurements for adjusting a thermal expansion valve). The pressure sensor  416  and temperature sensor  418  may be as described and shown in  FIG. 2  for either of the sensor inputs  220  and  222  described for measuring subcool and  224  and  226  described for measuring superheat. AC kit  402  preferably also includes indoor temperature probe  420 , humidity probe  422 , and outdoor temperature sensor  424 , which may be as described for indoor temperature probe, humidity sensor, and outdoor temperature sensor inputs  228 ,  230 , and  232 , respectively, described and shown in  FIG. 2 . 
     The AC/R kit  404  includes everything in the AC kit  402  plus the additional sensors, sender units, probes, or modules needed to provide the main unit  120  with the sensor input information needed for measuring both superheat and subcool. For example, AC/R kit  404  preferably includes all the sensors and probes  416 ,  418 ,  420 ,  422 ,  424  in the AC kit  402  plus an additional pressure sensor  426  (which may be substantially similar to pressure sensor  416 ) and an additional temperature sensor  428  (which may be substantially similar to temperature sensor  418 ). The AC/R kit  404  may include a combination of wired and wireless sensors, sender units, and transceivers/receivers as described and shown in  FIG. 3 , to provide a combination of wired and wireless remote sensor test and measurement means using a central/main unit  120 . 
     The Combustion kit  406  includes the sensors, sender units, probes, or modules needed to provide the main unit  120  with sensor input information for measuring CO 2  percentage, carbon monoxide (CO) percentage, CO ppm, inlet or ambient temperature, flue temperature, draft pressure, and gas pressure. For example, Combustion kit  406  preferably includes an oxygen (O2) sensor  430 , a carbon monoxide (CO) sensor  432 , a differential pressure sensor module  434  (for measuring draft and gas line pressures), a temperature probe  436  (for measuring temperature inlet combustion air entering the combustion chamber for ducted inlet combustion equipment or ambient air for ambient combustion air equipment), and a second temperature probe  438  (for measuring flue gas temperature past the heat exchanger, in the chimney of the heating system). The Combustion kit  406  preferably further includes an external unit  440  attachable to (for example, the back of) the main unit  120  and having its own power supply, the external unit  440  including, in one embodiment, the oxygen sensor  430 , the carbon monoxide sensor  432 , and the differential pressure sensor module  434 . The Combustion kit  406  preferably includes a flue gas sample probe  441 , for sampling flue gas in the chimney. 
     The Air Flow kit  408  includes the sensors, sender units, probes, or modules needed to provide the main unit  120  with sensor input information for measuring air flow velocity, air temperature, relative humidity, wet bulb temperature (calculated), dew point (calculated), change in dew point, and pressure differential. The Air Flow kit  408  preferably includes an air vane  442  for sensing air flow velocity, a low pressure probe  444  adapted to sense return air static pressure, another low pressure probe  446  to sense supply air static pressure (for differential pressure measurements across the blower), and indoor temperature and humidity probes  448 ,  450  as described for indoor temperature probe  228  and humidity sensor  230 , respectively, described and shown in  FIG. 2 . In one embodiment, low pressure probes  444 ,  446  provide measurement of return air static pressure plus supply air static pressure, the combined total being comparable with equipment specifications for determining proper system functioning and system performance. The Air Flow kit  408  may include an additional temperature probe  449  for measuring the temperature rise through the furnace and using the temperature difference to estimate air flow (CFM). Temperature probe  448  may be used to measure return air temperature, temperature probe  449  may be used to measure supply air temperature, and the difference between the two is the temperature rise/difference (TD). The air flow (CFM) may then be approximated as (the furnace output in Btu/hour) divided by (TD times  1 . 08 ). 
     The Electrical kit (E-kit)  412  includes the sensors, sender units, probes, or modules needed to provide the main unit  120  with sensor input information for measuring voltage, current, resistance, and other common electrical measurements (i.e. capacitance, frequency, duty cycle, diode function, temperature). The E-kit  412  preferably includes a voltage probe  468 , a current probe  470 , a resistance probe  472 , other probes such as, for example, capacitance, frequency, or temperature probes, and an external device  476  capable of converting measured parameters to a signal having sensor input information receivable by the main unit  120 . The external device  476  may also include common leads and attachments (such as, for example, a common ground lead), high impedance circuitry for voltage measurements, low impedance circuitry for current measurements, and circuitry for selecting between AC and DC measurements. The E-kit  412  may substantially comprise the functionality and features of a digital multi-meter combined with circuitry adapted to provide test and measurement information to the main unit  120  via sensor inputs  122 . 
     The Indoor Air Quality (I.A.Q.) kit  414  includes the sensors, sender units, probes, or modules needed to provide the main unit  120  with sensor input information for measuring CO 2 , air temperature, relative humidity, and pollutant concentration/detection. The I.A.Q. kit  414  may include an oxygen (O2) sensor  478  for measuring carbon dioxide percentage, a temperature probe  480 , a humidity probe  482 , and one or more pollutant sensors  484 . 
     A partial, generalized operational flow chart of a handheld HVAC/R test and measurement instrument  120  with kits  400 , according to various embodiments, is shown in  FIG. 5 . Other steps may be added, and steps may be omitted. However, operation of the main unit  120  preferably includes the following general steps, functionality, and features. Generally, sensor inputs  122  from a chosen kit of sensors (from a range of optional kits  400 ) are connected (step  502 ) with the main unit  120 , and the sensors (probes, sender units, etc.) associated with the chosen kit are connected to the system under test (step  504 ). Upon power up of the main unit  120  and any components of the chosen kit requiring power, and once the sensors are connected to the system under test and sensor inputs  122  connected with the main unit  120 , the main unit  120  automatically detects and verifies what is connected to it and (step  508 ) the tests, measurements, and analysis functions that may be performed using the sensor information available. That is, preferably, the main unit  120  automatically verifies the sensor inputs  122  (in terms of what type of sensor are connected and, also preferably, whether such sensors are working properly). The sensor input  122  information (i.e. sensor connections, sensor functioning status, sensor information being transmitted/received in real-time) is then provided to the main unit  120  for display to the technician/user. The main unit  120  preferably automatically monitors (step  510 ) the sensor inputs  122  for settled/steady state sensor measurement information and alerts the technician (visually, audibly, and/or tactilely) of the status of the connected sensors, status of the system  100  (for example, the settling of subcool or superheat measurements following a change in refrigerant charge, the presence of hazardous gas concentrations near the furnace warranting improved ventilation, whether the sensed measurement information is within typical/expected operating ranges), and the status of analysis or tests in-process or to be performed (for example, the status of data-logging). In one embodiment, the main unit  120  automatically monitors sensor inputs  122  and provides the technician with alerts and indications regarding safety conditions of workspaces, for example, alerting the technician if refrigerant is detected or if oxygen levels are becoming too low (or trending downward) so as to present workspace safety concerns. 
     The main unit  120  preferably provides the user/technician with real-time display of the sensor inputs  122  so the technician can watch the measurements/sensor inputs change in real-time. In preferred embodiments, the main unit  120  also provides the user/technician with real-time display of the (computed/calculated/estimated) output values (such as, for example, superheat, subcool, combustion efficiency, etc.) as those output values change in response to dynamically changing sensor input values. That is, the main unit  120  allows a technician to not only view all sensor inputs simultaneously, but also to view outputs/results/computations in real-time. In one embodiment, the main unit  120  allows the technician/user to enter “what if” input values or other parameters (such as, for example, a temperature value, refrigerant type, manufacturer model number, or other measured or referenced value that may influence calculated or estimated measurements such as superheat) to determine what impact, if any, such hypothetical input or reference value or parameters, if different, would have on the real-time displayed output values and results. 
     In most superheat or subcool measurements, it is recommended to start the HVAC/R system and let it run for 10-30 minutes to allow the temperatures and pressures to stabilize before taking measurement values. In preferred embodiments, as described previously, the main unit  120  includes programming instructions and circuitry adapted to monitor sensor inputs  122  in real-time and detect when system  100  temperatures and pressures have settled/stabilized (step  510 ). In one embodiment, the main unit  120  also provides the technician with an indication of the expected time that will be needed to reach such settled/stabilized system temperatures and pressures, enabling the technician to multi-task or focus on another activity during waiting periods. In one embodiment, the main unit  120  alerts the technician of settled sensor inputs (step  510 ). In preferred embodiments, the main unit  120  provides alerts to the technician when predetermined target values are reached. For example, the main unit  120  preferably provides the technician with step-by-step guidance for tests such as target evaporator exit temperature in addition to common testing for superheat, subcooling, and combustion. Once the target evaporator exit temperature (i.e. once supply air  148  exiting evaporator  114  in system  100  reaches a target value) the main unit  120  provides an alert to the technician. 
     The main unit  120  preferably automatically prompts the technician/user for user-input selections  514  such as refrigerant type, fuel type, parameters to view/display, or modes of operation of the main unit  120  depending upon the automatically detected sensor inputs  122  and automatically determined available measurements and analysis available to the user. The main unit  120  preferably (step  516 ) includes sufficient programming instructions to provide recommendations, suggestions for system performance improvement, troubleshooting guidance, and so forth, based upon the real-time monitoring of the sensor inputs  122 . Preferably, the user is able to scroll  518  through such automatically provided troubleshooting and analysis guidance information to select and drill down through menu information to access additional information and suggestions and to perform the desired system analysis. 
     In one embodiment, the main unit  120  provides the user access to not only suggested testing and measurement procedures and troubleshooting assistance, but also access to reference information and underlying practical application principles and best practices so as to present the user with the depth of vocational training and information available from technical handbooks commonly carried by field technicians, or, preferably, the in-depth reference information available from treatises such as the aforementioned Air-Conditioning, Heating, and Refrigeration Institute&#39;s published reference text. Such technical reference and training information may be stored on-board the main unit  120  or accessed by the main unit  120  via wi-fi, Ethernet, cell, or other network connection. For example, technical reference information may be accessed through a smartphone application designed for retrieval and mobile presentation to a field technician. Preferably, main unit  120  provides the user/technician access and prompts to relevant technical reference information that is in response to the main unit&#39;s determination of the kit of sensors  400  being used, the automatically detected and verified sensor input information being received, monitored, and presented for display to the user in real-time, and the automatically determined recommendation/troubleshooting/system analysis information. In preferred embodiments, main unit  120  provides the user with technical database information with possible causes for erroneous readings/measurements. 
     In one embodiment, the main unit  120  automatically saves into memory test and measurement information useful for typical system testing and analysis, and that is most commonly used when reporting system performance. The main unit  120  then alerts the user of the automatically saved data, providing the user options whether continue retaining the data in memory or allow the automatically saved data to be overwritten as additional memory is needed. The main unit  120  preferably (step  520 ) automatically prompts the user to save pertinent test and measurement results (in memory on-board the main unit  120  or storage accessible to the main unit  120 ) and provides the user with output options such as printing on a networked or connected printer, export data to a laptop or other device, or send data via email or to a smartphone, PDA, or other external device. The main unit  120  preferably prompts the user to save pertinent data and output typically used service and system performance reports, allowing the user to scroll (step  522 ) through such saving and reporting/output options. 
     Although different circuitry, hardware, and software arrangements/architectures may be used, an exemplary functional block diagram  600  of a handheld HVAC/R instrument (or main unit)  120  is illustrated in  FIG. 6 , in accordance with various embodiments. The main unit  120  preferably includes drivers and circuitry  602  for the display  126  and drivers and circuitry  612  for the key pad  130  and function/selection buttons  128 . Drivers and circuitry  604  and  608  are provided for the physical inputs  122  and physical outputs  124 , respectively. Physical inputs  122  may be any of a wide variety of configurations—USB, mini-USB, DIN, or other wired signal transmitting/receiving means. The main unit  120  is preferably equipped with drivers and circuitry  606  and  610  for wirelessly transmitting/receiving, respectively, sensor inputs  122  and main unit outputs  124 . The main unit  120  also includes an internal power supply  636  and audio drivers and circuitry  642 . 
     Databases  614 ,  616 ,  618  are preferably included in main unit  120  for providing troubleshooting, system analysis, improvements, possible causes of erroneous readings, user guidance steps/functions, and other technical reference information. Memory  622 ,  624 ,  626 ,  628  is preferably included for look-up tables (LUTs) and calculation algorithms needed to support the sensor kits  400 . On-board memory  630 ,  632 ,  634  that is writable by external devices such as, for example, laptop  208  or smartphone  210 , and via SD card, flash drive devices, etc. may be included in main unit  120  for loading additional or updated LUTs, software, customer ID information, and other data. Memory, LUT, and database management circuitry  638  is preferably included for handling software changes, updates, and operation of the main unit  120 . 
     Microprocessor  620  and supporting circuitry preferably provides the main unit  120  with processing means for executing stored programming instructions, access to on-board and accessible databases and memory, calculations, execution of algorithms, and other computing needs. Additional processing capacity  640  is preferably included for real-time monitoring and display of input data, preferably real-time monitoring of all inputs simultaneously or substantially simultaneously. 
     Instead of the main unit  120  receiving sensor inputs  122  and directly providing outputs  124 , in other embodiments of the present invention the function and capabilities of the central/main unit  120  may be divided, as shown (as system  700 ) in  FIG. 7 , into a handheld sized test and measurement data interface unit  702  for receiving sensor inputs  122  from sensor kits  704  and providing received sensor input information  706  to a handheld sized user interface  708 , which in turn provides outputs  712  in the same way as described herein for the outputs  124  from main unit  120 . The sensor kits  704  are as in  FIG. 4 , including kits  400 , as shown as kits  402 ,  404 ,  406 ,  408 ,  412 ,  414 . The interface unit  702 , in one embodiment, provides all functionality of the main unit  120  (for receiving sensor inputs from sensor kits  704 ) except for display  126 , key pad  130  and buttons  128  (i.e. most user interface functions) which are provided by the user interface  708 . The user interface  708  may also include databases  614 ,  616 ,  618  for providing troubleshooting, system analysis, improvements, possible causes of erroneous readings, user guidance steps/functions, and other technical reference information. In some embodiments the user interface  708  includes displays, key pad or user input features, and data processing capabilities. Functional components  710  in the user interface  708  may include a power supply (such as  636 ), memory/memory management circuitry (such as  638 ), databases  614 ,  616 ,  618 , and wired/wireless transmission/reception circuitry (such as  604 ,  606 ,  608 ,  610 ). 
     In one embodiment, the sensor interface  702  provides means for receiving sensor inputs  122  (from sensor kits  704 ) and transmitting sensor information  706  configured and arranged for reception by a user interface  708  such as a field portable tablet computing device, netbook, or smartphone device which can receive the transmitted sensor information and perform the data processing and user interface and feedback capabilities described herein provided by the main unit  120 . In another embodiment, the sensor interface  702  comprises all functionality and capabilities (and databases, data processing means, etc.) as main unit  120 , with the display  126  and user input features such as control buttons  128  and/or up, down, right, left, scroll, and select navigation controls  130  may be omitted in lieu of those user interface capabilities provided by an external device such as smartphone  210 . In such fashion the housing and components required for such a sensor interface  702  may be reduced in cost, size, and complexity, and a greater variety of devices may be used to provide the physical user interface for the technician. For example, the technician may choose to use a particular tablet computing device as a preferred user interface in combination with sensor interface  702  and sensor kits  704 . In such an embodiment, sensor interface  702  and sensor kits  704  provide all the functionality and capabilities described for main unit  120  herein, with the technician&#39;s choice of user interface device either substituting for display and physical user interface features not included with sensor interface  702  or complementing the display and physical user interface features and capabilities of sensor interface  702 . 
       FIG. 8  shows an exemplary functional block diagram  800  of a handheld sized data interface unit  702  as in  FIG. 7 , according to various embodiments. Preferably, functionally and physically, the combination of sensor interface  702  and the user interface  708  include all features and capabilities of the main unit  120  described previously. That is, in preferred embodiments, the sensor inputs  122  shown in  FIG. 7  and in  FIGS. 1-3  (and in all figures described herein) work in basically the same way, and, likewise, the user interface outputs  712  shown in  FIG. 7  work in basically the same way as main unit  120  outputs  124  in  FIGS. 1-3  (and all figures described herein). Drivers and circuitry  604  and  608  are provided for the physical inputs  122  and physical outputs  706 , respectively. Physical inputs  122  may be any of a wide variety of configurations—USB, mini-USB, DIN, or other wired signal transmitting/receiving means. The interface unit  702  is preferably equipped with drivers and circuitry  606  and  610  for wirelessly transmitting/receiving, respectively, sensor inputs  122  and outputs  706 . The interface unit  702  also includes an internal power supply  636  and audio drivers and circuitry  642 . 
     Memory  804 ,  806 ,  808 ,  810  is preferably included for data pertaining to function/operation of the sensor kits  400 . On-board memory  812 ,  814 ,  816  that is writable by external devices such as, for example, user interface  708 , and via SD card, flash drive devices, etc. may be included in interface unit  702  for loading additional or updated software and other data. Memory management circuitry  802  is preferably included for handling software changes, updates, and operation of the interface unit  702 . 
     Microprocessor  620  and supporting circuitry preferably provides the interface unit  702  with processing means for executing stored programming instructions, access to on-board and accessible memory, and other computing needs. Additional processing capacity  640  is preferably included for real-time monitoring and transmission of input data, preferably real-time monitoring of all inputs simultaneously or substantially simultaneously. 
     As mentioned above, the user interface  708  may comprise a smartphone (such as smartphone or PDA device  210  shown in  FIG. 2 ) with sensor interface  702  and any of a variety of sensors  704 , and the sensor interface  702  may be, in some embodiments, reduced in complexity to merely include means for receiving information from one or more sensors  704  and transmitting pertinent sensor information to a user interface  708 . 
     As shown in  FIG. 9 , a user interface  708  may comprise a Blue Tooth device  920  (for example, a Blue Tooth enabled smartphone) and may be used to wirelessly communicate with a sensor interface  702  that may comprise a power source and transmitter unit  936  adapted to receive sensor information from any of a variety of sensors  704  and transmit pertinent sensor information to the user interface  708 . In a preferred embodiment, the sensors  704  comprise any one or more attachment heads  904 ,  906 ,  908 ,  910 ,  912 ,  914 ,  916 ,  918 , or another sensor attachment head not shown, each of which preferably interconnects with the sensor interface  702 . The types of sensor attachment heads  704  shown in  FIG. 9  are exemplary. Other types of attachment heads may be used. Clamp head  904  may be used to sense current flow. Airflow head  906  may be used to sense air flow. RH/wet bulb/temp head  908  may be used to sense/determine relative humidity, wet bulb temperature, and/or general temperature. AC/DC amp clamp head  910  may be used to sense AC and/or DC current. Automotive DC clamp head  912  may be used to sense DC current. Carbon monoxide detector head  914  may be used to detect CO levels. And single pressure head  916  and dual pressure head  918  may be used to sense single and dual pressures, respectively. 
     In one embodiment, a sensor interface  702  comprises a base unit  922  adapted to receive any one or more sensor head attachments  704  and having wireless transmit and receive capabilities for wireless communications with a user interface  708 . The base unit  922  may be configured, for example, as a category III (CAT III) rated device (i.e. safety rated for use on permanently installed loads such as distribution panels, motors, and 3-phase appliance outlets) with display and user input functionality provided by a separate wirelessly connected user interface  708  such as handheld device/smartphone  920 . 
     As an example of a base unit  922  in combination with a sensor unit  704 , an IP67 rated meter  934  is shown in  FIG. 9  comprising a clamp-on type head  904 . Such meter  934  operates, according to a preferred embodiment, with a wirelessly connected user interface  708  such as a Blue Tooth enabled device  920  (or smartphone  210 ). Other types of base units may be used. An IP67 unit is safety rated for ingress protection—the “6” indicating total dust protection, and the “7” indicating protection in water submersion to a depth of 1 meter for at least a predetermined amount of time, typically 30 minutes. 
     As shown in  FIG. 9 , base unit  922  and IP67 meter  934  are exemplary configurations operable with a wirelessly connected device  920  whereby the device  920  preferably provides a display and other functionality of a user interface  708 . In other embodiments, the base unit  924 ,  926 ,  928  as indicated in  FIG. 9  include means for wirelessly communicating with a wireless device  920  which may comprise a user interface  708 , and/or means for communicating with a sensor interface  702  such as the power source and transmitter unit  936 . In preferred embodiments, any of the base units  924 ,  926 ,  928  may be attached to a particular sensor  704  (i.e. attachment head  904 ,  906 ,  908 , etc.) and wirelessly communicate with one or more device  920 /user interface  708  and/or wirelessly communicate with one or more sensor  704  via its associated sensor interface  702 . 
     For example, a base unit  924  may comprise a CAT IV rated device (i.e. a device rated for use in locations where fault current levels can be very high, such as supply service entrances, main panels, supply meters, and primary over-voltage protection equipment), such as a G3 Phoenix refrigeration instrument (manufactured by Universal Enterprises Inc.) with single display and wireless communications circuitry for wireless communication with either or both a Blue Tooth device  920  (such as an iPhone or other smartphone, for example) and one or more wireless power source and transmitter  936  with its connected sensor head  704 . If the G3 unit  924  is connected to a single pressure sensor head  916 , for example, the G3 unit  924  preferably provides functionality of a user interface  708  for both its own directly (wired) connected sensor head  916  as well as, for instance, a power source/transmitter  936  attached to a carbon monoxide detector  914 , with the CO detector  914  capable of being remotely located from the G3 unit  924 . Further, a separate wireless device  920  may also be used by the technician as a user interface  708 . The technician may use the wireless device  920  to monitor both the CO detector  914  via its transmitter  936  and also the single pressure sensor  916  via the G3 unit  924  and its wireless transmitter. 
     In similar fashion, in preferred embodiments, the technician may use the wireless device  920  to simultaneously and/or selectively monitor additional wireless enabled base units with respective attached sensor heads, additional base units in wireless communication with other remotely located (wirelessly enabled) sensor units/sensor interface units, and/or other wirelessly enabled base unit devices. In preferred embodiments, any of the wireless capable units  924 ,  926 ,  928  may, as illustrated in  FIG. 9 , communicate wirelessly (such wireless communication shown in  FIG. 9  in dashed line) with one or more transmitter  936  equipped sensor heads  704  (i.e.  904 ,  906 ,  908 ,  910 , etc.) and with one or more wireless device  920 , or even (not shown) other wireless capable units  924 ,  926 ,  928 . 
     As shown in  FIG. 9 , unit  926  may comprise a CAT III rated G3 Phoenix-type device with two displays, true RMS, and equipped with wireless communications capabilities/circuitry. Unit  928  may comprise a CAT III rated G3 Phoenix-type device with two displays and wireless communications capabilities/circuitry. Other configurations for the units  924 ,  926 ,  928  may be used, which preferably include user interface  708  functionality and means for wirelessly communicating with a transmitter  936  and/or wireless device  920 . 
     In preferred embodiments, each of the units  922 ,  924 ,  926 ,  928 ,  930  may be directly (wired) connected with any of the sensor attachment heads  904 ,  906 ,  908 ,  910 ,  912 ,  914 ,  916 ,  918 . Unit  930  is illustrated as an exemplary user interface unit that does not include wireless communications means. Unit  930  may comprise, for example, a CAT III rated G3 Phoenix-type test and measurement instrument with two displays, temperature, but no wireless communications means. Preferably, such unit  930  may be configured to receive and directly (wired) connect with any one of the sensor attachment heads  904 ,  906 ,  908 ,  910 , etc. (as indicated for units  922 ,  924 ,  926 ,  928 ). In one embodiment, a wired adapter  902  may be used to directly (wired) connect unit  930  or any unit  922 ,  924 ,  926 ,  928  with any of the sensor attachment heads  904 ,  906 ,  908 , etc. The wired adapter  902 , in preferred embodiments, allows for physical separation between the unit  930  (or other base unit  922 ,  924 ,  926 ,  928 ) and the sensor  704 . For instance, a technician holding a G3 unit  930  may use a wired adapter  902  to connect the G3 unit  930  to an air flow head  906  that may be positioned in a hard-to-reach area (eg. air duct space) at a distance (substantially the length of the wired adapter  902 ) away from the technician holding the G3 unit  930 . 
     By way of comparison with meters having greater features and capabilities, the clamp-on meter  932  show in  FIG. 9  is illustrate as a low cost current and temperature meter without a capability for accepting (attaching to) different sensor attachment heads  904 ,  906 ,  908 ,  910 , etc. and without any wireless communications mean / circuitry. The unit  932  is shown as a “UTL” brand low cost meter. UTL meters such as the UTL  260  Digital Clamp-on meter are distributed by Universal Enterprises Inc. (UEi). 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.