Z-метр DX4090 User Guide Version 1.03 RMT Ltd Moscow, 2015 Z-Meter DX4090 RMT Ltd CONTENTS 1. INTRODUCTION ........................................................................................................................... 3 1.1. Objectives ................................................................................................................................ 3 1.2. System Requirements .............................................................................................................. 4 2. TECHNICAL CHARACTERISTICS ................................................................................................ 4 2.1. Z-Meter Specifications ............................................................................................................. 4 2.2. Other Features ........................................................................................................................ 4 2.3. Standard Delivery Kit ............................................................................................................... 5 3. DESCRIPTION .............................................................................................................................. 6 3.1. Design overview. ...................................................................................................................... 6 4. WORKING WITH Z-METER .......................................................................................................... 7 4.1. External connections. ............................................................................................................... 7 4.2. USB Drivers Installation ........................................................................................................... 7 4.3. Software Installation ................................................................................................................. 8 5. MEASUREMENT OF TE MODULES PARAMETERS .................................................................... 9 5.1. TE Modules Connection ........................................................................................................... 9 5.1.1. Measurements of TECs in internal chamber. ...................................................................... 9 5.1.2. External TEC measurements ............................................................................................. 9 5.2. Working with Program ............................................................................................................ 10 5.3. Program Main Window ........................................................................................................... 10 5.3.1. Menu Bar ......................................................................................................................... 11 5.3.2. Reference Bar .................................................................................................................. 11 5.3.3. Functional Fields .............................................................................................................. 12 5.4. Measurements of R, Z, ........................................................................................................ 13 5.4.1. Temperature Setting......................................................................................................... 13 5.4.2. TE Module Type ............................................................................................................... 13 5.4.3. Corrections Field .............................................................................................................. 14 5.4.4. Parameters for Header Thermal Resistance .................................................................... 14 5.5. Measurement Procedure and Notes....................................................................................... 15 5.6. History 17 5.6.1. File ................................................................................................................................... 17 5.6.2. Options............................................................................................................................. 18 5.6.3. Report .............................................................................................................................. 18 5.7. TE Modules Database Update ............................................................................................... 19 6. TEC DYNAMICS PROCESSING ................................................................................................. 21 6.1. Time Constant Measuring ...................................................................................................... 21 6.2. Interpolation Results .............................................................................................................. 21 7. FIGURE-OF-MERIT Z MEASURING ........................................................................................... 22 7.1. Single-stage TE Module Z ...................................................................................................... 22 7.2. Two-stage TE Module Z ......................................................................................................... 24 7.3. Alternative Correction............................................................................................................. 25 8. MEASURING PROCESSES ........................................................................................................ 25 8.1. AC Resistance Measurement................................................................................................. 25 8.2. Measurement of U and Uα Telemetry ..................................................................................... 26 8.3. Voltages Measurement for Testing Z ..................................................................................... 27 8.4. Checking of TE Module Polarity ............................................................................................. 27 9. MAINTENANCE.......................................................................................................................... 28 Page 2 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 1. INTRODUCTION 1.1. Objectives The Z-Meter provides measurement of following parameters of thermoelectric (TE) modules (also TE coolers, TECs): AC Resistance (R), Figure-of-Merit (Z), Time Constant (). Maximum Temperature Difference* (Tmax) * For thermoelectric coolers (TECs) the measured Figure-of-Merit allow to calculate additional performance parameter - maximum temperature difference Tmax. The calculation is valid for singlestage TECs. Measured Z for multistage TECs correlates with the cooling capacity, but no possibility for simple calculation of it. The parameters are measured at the ambient temperature. The software provides recalculation of TEC resistance and maximum temperature difference to other ambient temperatures if required. The Z-Meter allows testing of various types of single- and two-stage TE modules and submounts with a single-stage coolers. It also allows evaluation of quality of more-stage TE modules by measurement of their AC resistance. The Z-Meter is operated by computer under the operating system MS Windows: 98/2000/XP/Vista/7 or higher. ADVANTAGES Express testing performance of single stage and multi-stage thermoelectric modules Testing performance of TE modules integrated into optoelectronic devices (photodetectors, lasers etc.) Time constant measurement Compatible with other Z-Meters of RMT’s Devices Family. Version 1.03 / 2015 FEATURES Portable design Current adjustable in a range 0...80 mA Measurement at direct and reversed current Results normalization to standard temperatures Correction coefficients to Z value Low power consumption Page 3 of 28 Z-Meter DX4090 RMT Ltd 1.2. System Requirements Any Z-Meter requires connection to a PC and installation of “Z-meter” software. The software is delivered along with Z-Meters or may be downloaded from www.rmtltd.ru. The interface is simple and does not require User's special knowledge ore experience. General system requirements are as follows: Free USB port, 20 MB free hard drive space (additional space may be required later to store database for various types of coolers), Mouse or compatible pointing device. 2. TECHNICAL CHARACTERISTICS 2.1. Z-Meter Specifications Parameters Units Values Electrical resistance Range Ohm 0.1...100 Accuracy % 0.6 (but>0.01Ohm) Repeatability % 0.3 Figure-of-Merit Z Range 10-3/K 1...4 Accuracy % 1.5 Repeatability % 0.4 Time Constant Range s 1...100 Accuracy % 1.5 Repeatability % 1 Power Supply Voltage V 5 (USB connector) Current mA 250 Operational Conditions Ambient temperature °C 15...35 range Relative humidity % 0...95 Mechanical Parameters Dimensions mm 160х66х30 Weight kg 0.24 °C Storage temperatures -20…+60 range % Humidity 5…95% 2.2. Other Features - The Z-meter has an internal chamber for placing a TEC under measurements. It is always recommended to place TECs into this chamber. If TEC size does not fit the chamber, such a TEC may be placed outside and connected to Z-meter by external cable enclosed. In both cases, four-wire connections are used to ensure the most precise measurements. Note free air convection around the TEC is required in case of measurements of TECs outside the internal chamber.. - The Z-meter allows checking of TEC polarity simultaneously with TEC parameters measurement. Page 4 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 2.3. Standard Delivery Kit Z-meter DX4090 1 pcs. Cable with 4-wire terminals for external testing * 1 pcs. Cable USB AM / miniUSB-B 1 pcs. CD or USB Flash (Software, Manual) * Measuring terminals can be made on the basis of Kelvin klips of various designs. Version 1.03 / 2015 Page 5 of 28 Z-Meter DX4090 RMT Ltd 3. DESCRIPTION 3.1. Design overview. The Z-meter is a single-unit device with internal chamber for TECs. Chamber’s cover is magnetically locked when closed or opened. The internal chamber is a passive thermostat which provides constant TEC temperature during measurements. Terminals inside allow easy connection of measured TEC. Temperature inside the chamber is measured by an appropriate thermosensor. There is also a heater inside the chamber for measurement of TEC polarity. There is also a LED for visual control of measurements status. USB connector for connection to a PC, and connector for a cable for external TEC measurements are located on the back of the device. T0C Hbridge Precision current source Instrumentation amplifier switch DAC ADC Microcontroller Internal connection Heater External connection switch USB driver current source Z-meter: back view and functional scheme Page 6 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 4. WORKING WITH Z-METER 4.1. External connections. Connect Z-meter to USB port of your PC. Connect the cable for external measurements to the connector Ext if you plan external characterization of TEC(s). Otherwise this cable should not be disconnected to the Z-meter. 4.2. USB Drivers Installation Install USB drivers using enclosed CD/flash. The latest versions of drivers are also available at http://www.ftdichip.com/Drivers/VCP.htm . Installation procedures for a specific version of Windows may be also found at http://www.ftdichip.com/Support/Documents/InstallGuides.htm USB Serial Converter should appear in the Windows Device Manager after successful installation. Version 1.03 / 2015 Page 7 of 28 Z-Meter DX4090 RMT Ltd 4.3. Software Installation Insert the CD/flash to a PC and start the Setup program. The window of the standard Windows installer will appear – see below. Click “Install” and proceed according to the installer directions. Remember at least 20 MB of a space should be initially available at selected logic disk, and that the size will increase when you’ll add new TECs to a database with measurement results. Page 8 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 5. MEASUREMENT OF TE MODULES PARAMETERS TECs and Z-meters must be kept at ambient conditions expected during tests for at least of one hour before any measurement. If any Z-Meter was stored at / subjected to temperatures below +10°C before measurements, it must be kept at expected ambient test conditions for at least 2 hours. 5.1. TE Modules Connection 5.1.1. Measurements of TECs in internal chamber. Open the cover of the Z-Meter. Connect TEC to terminals firmly (see left). Close the cover and run the Z-Meter program. 5.1.2. External TEC measurements Connect your TEC firmly as shown below. Ensure minimum possible air convection in the area of measurement. It is recommended to place the TEC as close to the Z-meter as possible keeping internal chamber opened. Remember temperature sensor is located in the chamber and considerable difference of TEC and thermosensor’s temperature will result in mistakes in measurements. Note TEC polarity check option must be switched off in case of external measurements. Version 1.03 / 2015 Page 9 of 28 Z-Meter DX4090 RMT Ltd 5.2. Working with Program The Z-meter must be plugged-in to PC before running the Program. The following windows will be displayed one after another in case you run Z-meter program for the first time, see below : If the “DEVICE NOT FOUND” message pops up, please make sure the device is properly connected. Also check whether the USB drivers have been properly installed and repeat USB driver installation procedure if required ( see 4.2. above). 5.3. Program Main Window The main program window is shown in the screenshot below. Result field Dynamics field Corrections field Device info field Page 10 of 28 Control field Type connector & Use Check Polariry Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 Its functional structure is the same for three Z-Meter measurement options: Single-stage TE module; Single-stage TE sub-mount; Two-stage TE module. 5.3.1. Menu Bar There are four items in the Menu bar. "File" is used when it is necessary to reconnect the Device or exit. "Options" allows: 1) adding/editing a TE module type; 2) selecting a TE module (TEC) database; 3) choosing a TE module (Cooler) type; 4) enabling/disabling check polarity TE module (internal TEC connection only) "History" allows switching from current measuring results to database with previous measurements. "Help" provides information concerning the Z-Meter software 5.3.2. Reference Bar There are two fields in the Reference bar. The field "Cooler type ID" allows selecting a TE module type to be tested. The field "Reference T" serves for the reference temperature input. The values R and ∆Tmax displayed will be recalculated to this temperature. The temperature step is 0.1 K. You may also choose a value from standard reference temperatures which are 20°C or 30°C, or ambient. Version 1.03 / 2015 Page 11 of 28 Z-Meter DX4090 RMT Ltd 5.3.3. Functional Fields There are four functional fields in the main window: Control” field presents the following test parameters: electric current, total time of measurement, time step. The button "Measure" starts the measuring procedure. Dynamics field depicts the chart window of the Seebeck voltage U(t) temporal behavior telemetry It also indicates obtained values of: 1) Time constants at different current polarities, 2) Z at different current polarities Corrections field shows the important calculated corrections values which will be used for calculation of them main performance parameters like, for example, Z (see Chapter 7 for details). . Following possibilities of a correction exist : 1) Default - using of the calculated corrections (only for the TE modules fully described in the database); 2) Manual - using a User's own coefficient value A, manually inputted; 3) None – no use of any correction. Results field contains the following measured/calculated results: 1) Electrical AC resistance R of the TE module; 2) Ambient temperature Tambient; 3) Figure-of-Merit Z of the TE module (for two polarities and averaged); 4) Maximum temperature difference ∆Tmax of the TE module (for two polarities and averaged); 5) Time constant of the TE module (for two polarities and averaged). Page 12 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 5.4. Measurements of R, Z, 5.4.1. Temperature Setting Z-meter allows re-calculation of the main TEC parameters to various temperatures (see Chapter 7). The RMT's standard temperature is 27°C, other manufacturers may apply their own values. The most convenient ambient temperature to which the parameters are recalculated may be selected from a “Reference T” list of entered manually. 5.4.2. TE Module Type Select a "Single-stage" or a "Two-stage" option following " Option>> Cooler Type". Note if no option is chosen, corrections are set zero. If serial number of the testing is known or identified (in a case of testing of RMT TECs) set the s/n using Cooler type ID from listed database at reference Bar In the case software will extract default corrections factors for the particular TEC type in the field of corrections If type is unknown then the state is “Default”. If the TEC type is not listed into software database one can stay correction coefficient as 1, or to set own corrections coefficients if they are known of can be calculated. Automatic notice will appear if any TEC parameter required for further calculations is missed. Add correspondent parameter to the database. Version 1.03 / 2015 Page 13 of 28 Z-Meter DX4090 RMT Ltd If necessary TEC type is absent in the list, add module parameters to the database manually (see Chapter "Database Update"). 5.4.3. Corrections Field Attention! If no information on parameters of tested TEC is available in the database, no corrections/coefficients will be used in calculations of TE module parameters by default. “TE Cooler Type” field will change to DEFAULT in this case. With all TEC parameters available, the corrections as well as their equivalent coefficient А are taken into account by default (see Equation 7.3.1). The corrections are specified in the Table below. It is possible to switch particular correction on/off by correspondent radio button pairs. The Results window fits the changes automatically. Symbol bT b th Description Allows for the inequality of the ambient temperature and the average temperature of a TE module Allows for additional heat fluxes between pellets ba Allows for external heat fluxes br Allows for additional electrical resistance of leading wires Comments For single-stage modules only For single-and twostage modules For two-stage modules only For single-and twostage modules In other words, any user is given an opportunity either to take into account the corrections via the calculated values selected by a User and their equivalent coefficient А (by default), or to suggest one's own value of A, or to refuse all the corrections. 5.4.4. Parameters for Header Thermal Resistance Z-Meters also allow characterization of TE cooler sub-assemblies by choosing correspondent option in the Manu. In this case, however, following parameters should be available/ added: 1) the header material thermal conductivity; 2) the header base thickness; 3) the mounted TE module fully described in the Z-meter database. Page 14 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 5.5. Measurement Procedure and Notes Reference Temperature Set required reference temperature at reference Bar. Default - 27 °C (300K). Parameters of measurement In “Control” field one can set parameters of measurement Working Current Recommended value is 1% of Imax according to specification of examined TEC unit. If it is not known – use default – 5mA for the beginning. Time of measurement Set the total measurement time. Recommended value – more than 5-6 of time constant of the TEC. If the value is unknown set stay default – 10 second for the beginning. Time step Recommended value – 20 millisecond. Measurement cycle is started simply clicking “Measure” in the Program Main Window. Attention! The temperature of a TE module changes slightly owing to hands touching. Besides, the measuring procedure induces a slight TE module average temperature increasing. So keep a pause of at least 3x measured time constant before any new measurement. It is usually 30 sec on average. This time is usually enough to stabilize the TE module temperature. The message: appeared shortly after clickinmg “Measure” means that either: open circuit inside the TE module, short circuit inside the TE module. Version 1.03 / 2015 Page 15 of 28 Z-Meter DX4090 RMT Ltd Note the last case is hardly possible in practice according to RMT’s experience. Therefore, open circuit is more likely the reason. Double-check the terminals for proper contacting TEC. Retry measuring. Occurring of the message indicates on TE module failure/malfunction. Attention! Selection of a too higher TEC control current (see the Main Window) may result in exceeding of a full scale of ADC used. The message as shown below will be generated automatically. In such a case, select the value recommended for measurements and try again. If everything is OK at Graph field you will observe curves of Seebeck voltage measurement in time under applied working current. After two curves appear (direct and reversed current measurement) the software will calculate all measured parameters Reference resistance temperature) Page 16 of 28 (at reference Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 As mentioned above, the DX4090 Meter may be also used for measurement of AC resistance in coolers with more than two stages. To do this, leave the "TE Cooler Type" unselected (Default Type in the "TE Cooler Type" field). Insert a TE module into the DX4090 Meter and click the "Measure" button. Note you must ignore all the results except the resistance value in such a case. 5.6. History 5.6.1. File The results of each measurement are stored in the file. You can view or clear it using the "File" command. The history file is created in the "/History"l folder of the "/Zmeter" directory during every measuring session after the first successful measurement. ("Measuring session" means the period between the first successful measurement and the program exit). The history file name has the form of the date and time of the history file creation. "Comment" field on the top of the "History" window allows adding of additional comments to history files. If you need to save the "History" file under other name, use the "Save As" command. The "New" command closes the current history file and opens a new one with no data. Data arrangement in the "History" window is represented below. The "Chk" field is assigned for records marking. Note only marked records will be copied on a printer under the "Print" command. The marking/unmarking is performed with the mouse left button click on the appropriate field. The default record state is "Marked". Version 1.03 / 2015 Page 17 of 28 Z-Meter DX4090 RMT Ltd 5.6.2. Options If menu item "Auto Save" is checked, the "History" file will be saved automatically. 5.6.3. Report With the "Print" command you can make the hard copy of the "History" file on a default printer. Submenu "Export" will help you to keep a «History» file in various formats: The example of Preview Report is shown below. Page 18 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 5.7. TE Modules Database Update If the parameters of any TE module are not available in the database, you can add them by yourself. The full set of parameters consists of: 1) TE module cold and hot sides dimensions; 2) Pellets number (for a two-stage TE module the pellets numbers ratio); 3) Pellet cross-section; 4) Pellet height; 5) Leading wires material, 6) Leading wires length, 7) Leading wires cross-section. Choose the database you want to change (see the figure above, example only). Select the "File" -> "TEC Base Editor" command from the "Main" menu. The window titled "Add TE cooler" will appear. There are two input boxes in the window: "Cooler" and "Leads". All or a few fields may be already filled in. Enter correct/required parameters by yourself when required. Version 1.03 / 2015 Page 19 of 28 Z-Meter DX4090 RMT Ltd The contents of "Cooler ID" field are not used for calculations. You can fill any information in this field. You can also edit or delete a TE module existing in the database. To do it just select the TE module, make appropriate changes in the data and click on the "Add/Modify" button. To remove the TE module from the database, select it and click on the "Delete" button. Page 20 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 6. TEC DYNAMICS PROCESSING 6.1. Time Constant Measuring Let us consider a single-stage TE module. The ambient temperature is Ta. At a certain moment electric current is applied to the module. The differential equation describing transient dynamics for a pellet of the TE module can be presented as the following exponential superposition: (6.1.1) where ∆T(t,x)=T-Ta, T is temperature of the pellet point located at a time t and a generalized coordinate х, Un and mn are the eigenfunctions and eigen-values, An are thermal amplitudes, ∆Tst(x) is stationary ∆T value. The solution (6.1.1) analysis yields that the cooling process can be divided into two stages: irregular and regular. The first one is dictated by the initial moment's conditions and is described by a multiexponential interference. This phase fades out rather quickly and in case TEC pellets thermal conductance is high enough, the temporal behavior can be characterized by the only exponent, i.e for all possible n: (6.1.2) The theory yields the following expression for the time constant =1/mmin of a single-stage TE modules: (6.1.3) Here C1 ,C2 are TE module cold side and hot side heat capacities, α - TE material Seebeck coefficient, - TE material thermal conductivity, N - TE module pellets number, L - pellets height, s - pellets cross-section, j - electric current density. As Eq. (6.1.3) shows, calculation is stumbling because in practice the values involved are never known with accuracy required. The Z-meter allows measuring time constants of single-stage TE modules and estimating those of more-stage ones. 6.2. Interpolation Results The procedure of handling the time constant measurement data is as follows. The temporal behavior of a single-stage TE modules temperature difference is measured via the Seebeck voltage that is a corresponding proportional value: (6.2.1) Version 1.03 / 2015 Page 21 of 28 Z-Meter DX4090 TE module time constant τ is the time during which TE module temperature difference ∆T grows from 0 to 0.63∆Tst (Tst is steady state T value) at electric current turned on. RMT Ltd For a two- or more-stage TE module this simple ratio is not applicable. However the time constant can be estimated by the temporal dependence of the Seebeck voltage and the approach for obtaining the stationary voltage values is the same. The measuring procedure is carried out both for two electric supply polarities. The data collection duration and time step can be varied. The measuring time duration and step can be varied, too. The measuring chart window is presented on the Figure below. Measuring window of TEC dynamics The obtained experimental data is then fitted by the following function: (6.2.2) The exponential regression is based on the method of least squares. As its outcome, the procedure provides the time constant and the stationary Seebeck voltage Ustα. 7. FIGURE-OF-MERIT Z MEASURING 7.1. Single-stage TE Module Z Among the parameters (R, Z, ∆Tmax, τ), measured by the Z-Meter the AC resistance R is the only measured directly. The R measurement method is described in the Section "AC Resistance Measurement". The determination of the Figure-of-Merit Z and the maximum temperature difference ∆Tmax of a TE module implements an indirect method, which allows avoiding labour-consuming thermophysical measurements. This approach is based on the Harman method. The Figure-of-Merit is one of most important parameters of a TE module. In a simplified form it may be defined as: (7.1.1) Where: α − TE material Seebeck coefficient, Page 22 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 R − TE module pellet electric resistance, k − TE module pellet thermal conductance. Hereinafter we deal with the stationary mode values only ( if not mentioned otherwise, see Section 6.1). The base equations that describe a single-stage TE module thermal balance are as follows: (7.1.2) where I - electric current, R - electric resistance of a TE module pellet, T0 - TE module cold side temperature, T1 - TE module hot side temperature, Ta - ambient temperature, N - TE module pellets number, a0 - heat exchange coefficient for the cold side, a1 - heat exchange coefficient for the hot side, k' - efficient thermal conductance of a pellet allowing for additional heat fluxes between the pellets. We assume that the heat exchange coefficients meet the following requirements: (7.1.3) We also suppose that electric current is small: (7.1.4) We recommend the measuring current See Imax values in the TEC specifications To the accuracy of the first-order infinitesimals of the values (7.1.3) and (7.1.4), we obtain for Z: (7.1.5) Where Uα = Nα(T1 - T0) is TEC Seebeck voltage, UR = NIR is TEC Ohmic component of the voltage. The ratio of the voltages Uα and UR in Eq. (7.1.5) must be averaged for two directions of the current (the index av=average), as it eliminates expressions depending linearly on the current and allows extracting the corrections bth, br, bT. The value bth is the correction for additional heat flux between the pellets; br is the correction for leading wires electric resistance; bT is the correction allowing for inequality of the TE module average Version 1.03 / 2015 Page 23 of 28 Z-Meter DX4090 RMT Ltd temperature and the ambient temperature. The values a0, a1 are estimated with account of free convection in the air and of thermal radiation: a0,1=(αconv+αrad)S0,1, where αconv, αrad are thermal exchange coefficients of convection and of heat emission calculated for each TE module individually, S0 and S1 are the surfaces of the cold and hot sides of the TE module tested. Eq. (7.1.5) remains fair if inequalities (7.1.3) are modified as: (7.1.6) That means that the method allows finding the value Z of a TE module when the heat exchange on one side of the module is intensive enough. Therefore, the Z-Meter enables testing of a TE subassembly: TEC mounted on a header. In this case the value a1 is the header thermal resistance (calculated by the Program). The measured Z of a single-stage TE module allows estimating ∆Tmax of the module at the hot side temperature Т1: (7.1.7) 7.2. Two-stage TE Module Z For a two-stage TE module Z can be estimated with the help of the Harman method and can only be regarded as a criterion of an average quality of pellets if certain requirements are met. Here are heat rate equations for a two-cascade TE module: (7.2.1) Here T0,1,2 substrates temperatures, Ta - ambient temperature, N1,2 - numbers of pellets on the stages, a0,1,2 - heat exchange coefficients for the cold, hot and medium substrates, respectively. Let us assume that the ratios of the heat transfer coefficients a0 and a2 from the surfaces S0 and S2 to the pellets number N1, N2 are the same: (7.2.2) Page 24 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 The first and third equations of (7.2.1) can be written as: (7.2.3) If temperature differences on the cascades can be considered equal: ∆T1=∆T2 , (7.2.4) we obtain: (7.2.5) In real testing Eq. 7.2 is not rigorous, and Z 7.2 is only a relative criterion of a TE module quality. Here bth is the correction for additional heat flux between the pellets; ba is the correction for external heat fluxes; br is the correction for leading wires electric resistance. The value a is estimated by the software taking into account free convection in the air and heat emission. Averaging the voltages ratio (7.2.4), though mathematically not obligatory, is carried out similarly to a single-stage module case for accuracy purposes. 7.3. Alternative Correction It is convenient sometimes to reduce all the corrections discussed above to a certain coefficient А. Then Eqs. (7.1.5) and (7.2.5) can be written as: (7.3.1) The coefficient А can be also obtained empirically by correlating directly measured ∆Tmax and the value obtained by Z-Meter. 8. MEASURING PROCESSES 8.1. AC Resistance Measurement AC resistance is measured by applying a small AC signal to TE module. The AC is generated by a “Commutator” (swtich), which periodically (with 50% duty circle) reverses a circuit of the reference current Im. The “Commutator’s” simplified diagram is shown below. If there is no input signal, the output voltage of the instrumentation amplifier equals Em/2, where Em= 4.096 V. AC R testing simplified diagram Version 1.03 / 2015 Page 25 of 28 Z-Meter DX4090 RMT Ltd Output signal of instrumentation amplifier when AC R is tested During AC resistance measurement the output voltage of the instrumentation amplifier is sampled and measured by a 12-bit ADC each time before reversing the current Im.. The sampling points are marked as ti in Fig. 8.1.2. The voltage drops on TE module for the positive signal (Upi) and negative signal (Uni) are used for a TE module resistance (R) calculation by the following formula: (8.1.1) where AV - voltage gain of the instrumentation amplifier; n - total number of readouts per measurement. Typical values of parameters in formula (8.1.1) are: Im = 2 mA AV = 5 or 50 n = 50 8.2. Measurement of U and Uα Telemetry During measurement of the parameters U and Uα, a small current IT is applied to TE module periodically (with 50% duty cycle). Two successive measuring sessions are necessary to obtain the U and Uα values at different testing current polarities. Testing current and voltage schematic temporal behavior Page 26 of 28 Version 1.03 / 2015 RMT Ltd Z-Meter DX4090 8.3. Voltages Measurement for Testing Z Equations (7.1.5) and (7.2.5) contain both UR and Uα. These are the voltage values referred to the time at which the process becomes steady. Thus, the Seebeck voltage Uα in Eqs. (7.1.5), (7.2.5) is equal to the stationary value Ustα obtained by the interpolation procedure (see Eq. (6.2.2)). The Ohmic voltage drop UR is also calculated with reference to the steady-state time t. It should be done for the reason the TE module resistance R undergoes a change due to a slight evolution of its average temperature. At the current IT=0.01Imax it may have about 1-1.5 % growth. So, the value UR is resulted from the following averaging over the last 10 time points of the testing procedure at one current: (8.3.1) Make sure the measured TE module has reached the steady state. To assess it, the telemetry capability is available (see dynamics window) 8.4. Checking of TE Module Polarity To verify a TE module polarity the Z-Meter involves a procedure of a short-time heating of the bottom substrate of the module when finishing the procedure of voltage measuring on "direct" polarity. The averaged voltage U'α measured while heating is compared with the value Uα averaged over last 10 points of Uα: (8.4.1) If the TEC polarity is right: (8.4.2) In case of the polarity confused: (8.4.3) Version 1.03 / 2015 Page 27 of 28 Z-Meter DX4090 9. RMT Ltd MAINTENANCE The Z-Meter does not require any particular maintenance or service. Nevertheless if for any reason you feel doubtful about the device accuracy, you can check it by measuring a precision resistor instead of a TE module. The “R-meter” program should be used. We suggest measuring a resistor of 5 to 20 Ohms. Measure the resistor by “R-meter” program and digital multimeter with accuracy the same or better than 3 decimal digits. Compare the data obtained. If the difference in the resistance values is within 0.5%, the Z-Meter can be further used for measurements. WARRANTY RMT LLC warrants that the Z-Meter, if properly used and installed, will be free from defects in material and workmanship and will substantially conform to RMT’s publicly available specification for a period of one (1) year after date of the Z-Meter was purchased. RMT LLC also provides a 3-month warranty for the following parts and components included in the standard delivery set of the product: the cables, program disks and documentation If the Z-Meter fails during the warranty period RMT will repair the Z-Meter or replace it or its parts. For the warranty support a Consumer can address to the office of the company RMT or its sales representative. The product repaired or replaced in whole or in part, will have the warranty period counted as one (1) year from initial shipment but not less than 3 months upon shipping of repair/repalcement. TECHNICAL SUPPORT For the technical support and repair within and after the warranty period, please, address to the office of the company RMT or its sales representatives: In Russia and CIS RMT Ltd 46 Warshavskoe shosse, Moscow 115230, Russia Phone: +7-499-678-2082 Fax: +7-499-678-2083 e-mail: [email protected] In Europe, the USA and other countries TEC Microsystems GmbH Schwarzschildstrasse 3, Berlin 12489, Germany Phone: +49-(0)30-6789-3314 Fax: +49-(0)30-6789-3315 e-mail: [email protected] Fax: +49-(0)30-6789-3315 e-mail: [email protected] Page 28 of 28 Version 1.03 / 2015