Manual
Flow Division
INFOCAL 5 Energy calculator
Danfoss Flow Division operating under
Verification equipment Software version 1.00
[
SAP No.
521H1089
DKFD.PS.022.H2.02
Siemens Flow Instruments A/S as of September 1, 2003
]
*085R9446* FLOW DIVISION - SIMPLY BETTER
INFOCAL 5 Verificator
Contents
2
1.
Introduction ................................................................................................................... 3
2.
PC requirements ........................................................................................................... 3
3.
Software installation ..................................................................................................... 3
4. 4.1 4.2
Function ......................................................................................................................... 4 Verification according to EN 1434 ................................................................................. 4 Verification with connected tempera- ture sensors or decade boxes ........................... 4
5.
Connecting INFOCAL 5 test equipment to the PC ..................................................... 4
6. 6.1. 6.1.1 6.1.2 6.1.3 6.1.4 6.2. 6.3. 6.4. 6.5. 6.6. 6.7
Using the software program ........................................................................................ 5 Verification data .............................................................................................................. 5 Choose certificate template ........................................................................................... 5 Test points ...................................................................................................................... 6 Verification ...................................................................................................................... 6 Heat coefficients ............................................................................................................. 6 Passwords ...................................................................................................................... 6 Change of parameters under "Verification data" ........................................................... 7 Verification ...................................................................................................................... 7 Test data ......................................................................................................................... 8 Storing of data ................................................................................................................ 8 Certificate ....................................................................................................................... 8
7.
Calibration routine ........................................................................................................ 9
8.
Integration time (measuring time) ............................................................................. 11
9. 9.1
Calculation of measurement uncertainty ................................................................ 11 Assumptions for the calculation ................................................................................... 12 Uncertainty calculation for test point T1 ....................................................................... 13 Uncertainty calculation for test point T2 ....................................................................... 14 Uncertainty calculation for test point T3 ....................................................................... 15
10.
Possible improve- ments/adjustments of the measurement uncertainty ............. 15
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
1. Introduction
1.
The verfication equipment is used to test and verify the INFOCAL 5 energy calculator based on volume and high precision resistors simulating temperature values.
Introduction
The verification equipment offers you either a verification of the INFOCAL 5 itself or if required a verification of INFOCAL 5 with temperature sensors in a temperature controlled bath. Alternatively external resistor-decade boxes may be used. Verification equipment consists of a base part with simulation resistors, relays, a micro controller, net-adapter with 12 V AC, D-sub cable and diskettes with PC software. The calibration sequence is being controlled from the PC. The equipment is primarily designed for use in laboratories testing and verifying heat meters. It can also be used simply to test if the INFOCAL 5 is functional. Finally after verification a test certificate can be printed out and results stored. Template certificate language can be changed into local language. 2.
PC requirements
The PC must be an IBM compatible 486 or Pentium, with at least 8 MB RAM. To install the program at least 10 MB must be available on the hard disk, the PC must be equipped with a 3,5"/1.44 MB floppy drive. The program must be installed on the hard disk. Do not run the program directly from the floppy diskettes. The program will run under Windows WIN 95 or Win 98 and requires Excel program to be installed. The monitor has to be VGA as the programme is displayed in a VGA format. If the monitor has a better resolution than VGA, the menu displayed will be more compact and not fill the entire screen. COM port 1 or COM port 2 must be available for interface to the test equipment. The software programme can be set either to COM 1 or COM 2.
3.
Software installation
Check that the computer has at least 10 MB of space available on the hard disk. Carefully study the read-me file before starting the installation. Do not install directly from disc. For correct installation, copy disc to a temporary directory on your local driver. Close any other programs you have opened under windows before installing the programme. Insert floppy diskette # 1 into the diskette drive. Use "Start", "Run"- browse to C:\temporary and select "setup.exe". Follow the directions given by the program, insert diskette #2 when promted to do so. When installation is completed, an icon will appear on your monitor. The INFOCAL 5 Verificator can now be started from the program files.
DKFD.PS.022.H2.02
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INFOCAL 5 Verificator
4.
Function
4.1 Verification according to EN 1434
Verification is carried out as the equipment simulates 3 sets of forward and return temperature giving three test points: T1, T2 and T3. The test point is selected according to the test point required in EN 1434 which are: Selected value: EN 1434 requirements: 1. 3,5°K DQmin. < DQ < 1.2 x DQmin. 2. 19°K 10K < DQ < 20K 3. 145°K DQmax. –5K < DQ < DQmax. The test equipment contains precision resistors, which simulate the above forward and return temperatures. The resistor sets are connected to the INFOCAL 5 by use of high quality relays with double plated gold contacts sets. The design ensures minimum influence of the contact resistance on the test results. At delivery the actual resistor values are measured with a calibrated, traceable high accuracy instrument and entered into the E-prom in the verification unit. Even though the resistors are very stable, they must be re-calibrated on a regular basis to compensate for any drift in resistance. Preferably the calibration shall be performed under environmental conditions (room temperature) close to those under which the equipment later is operated. If the measured resistor-values differ from the preset values, the new values must be entered into in the program. The equipment simulates a water volume with a pulse frequency of 100 Hz generated in the micro controller. According to the preset integration time (test time for test point T1, T2, T3) in the program, a volume is simulated into the INFOCAL 5.
Example A INFOCAL 5 with 25 pulses/litre is tested on the verfication equipment. Integration time for T1 is set to 30 sec. 30 x 100 Hz = 3000 pulses 3000 pulses/25 imp/l = 120 litres The simulated "true" energy is calculated by the equipment as a function of the simulated temperature difference, the simulated water volume and the simulated temperature with respect to forward/return installation of the flow meter according to tables of heat coefficient from Dr. Stuck*). The software contains an automatic calculation of heat coefficient values, alternatively the heat coefficient values can be entered manually according to local requirements. The "true" energy is related to the measured energy by the INFOCAL 5. The measurement error (accuracy) of the INFOCAL 5 at the test point can then be calculated and presented in percentage of the true value. The measurement error presented in percentage in three different test points, T1, T2 and T3. Based on the "measurement error" and the dedicated MPE – values (Maximum Permissible Error) eventually reduced with the measurement uncertainty, the software decides if the heat meter keeps its verifications tolerances. A green or red flashing information field completes the verification. *)
4.2 Verification with connected temperature sensors or decade boxes
5.
4
Tabels and coefficient for water and heat-conveying liquid. ã1986 by Wirtschaftverlag NW, ISBN 3-88314-522-X.
Alternatively to the procedure stated in "4.1" the verification equipment can be used for other verification modes, e.g. OIML R 75 where it is allowed to verify energy calculators including sensor pair or as separate units at other test points than those stated in EN 1434. The software offers the possibility to stop the verification routine temporarily in order to move the temperature sensors from one bath to another or change resistor values on the decade boxes representing the forward and return temperatures. In this situation the wires in terminal 5 - 6 and 7 - 8 have to be disconnected from the internal resistors on the printed circuit board and replaced with the wires from the forward and return sensors or with wires to the decade boxes representing forward/return temperature.
Connecting INFOCAL 5 The 9 terminal D-Sub connector and the net-adapter must be connected and switched "On" before running the program. test equipment to the PC The 9 terminal D-sub connector must be connected to one of the COM ports of the PC. If COM port 2 is chosen remember to set COM port 2 active in the INFOCAL 5 verification program. The net-adapter is a 230 V AC to 12 V AC adapter. DKFD.PS.022.H2.02
INFOCAL 5 Verificator
6.
Using the software program
Remove the top cover and mount an INFOCAL 5 in the base part. (Device under test).
6.1.
Verification data
Start the INFOCAL 5 calibration/verification programme from the start menu or a shortcut on the dashboard. The program will automatically open the folder "Verification data" and a dialog box will appear. Note The dialog box only appears first time the programme is running. To open dialog box write "Setup" under folder "Verification data".
In order to verify INFOCAL 5 by use of internal reference resistors representing DQ = 3,5K, DQ = 19K and DQ = 145K click "OK" or make selection. The program is default set to:
Test points: Resistor based Verification at T1, T2, T3: No stops Heat Coefficients: Auto calculate Language select: English or Polish.
6.1.1 Choose certificate template
Create a directory for your certificates. Choose e.g. C:\CERTIFICATES or any other name you may find convenient. Even using a network drive is possible. Copy the the Excel file CerTemplate.xls from disc 4 to your certificate directory. This file is your certificate template (the empty certificate). CerTemplate.xls is in English, but can be modified to any language by any Excel user. To modify the template open the CerTemplate as read only. Save the new template under another file name with the extension “.xls”. Open the file for modification by inserting the password “danfoss” under tools - protection unprotect sheet or similar dependent on the Excel version you are using. Point to the text you want to change into your local language. To change into a local font select the field you want to change and then open format - cell - font and choose the desired font. Having finished the modification, open tools - protection - protect sheet and insert your password for protection of the template. Save the template.
DKFD.PS.022.H2.02
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INFOCAL 5 Verificator
6.1.2 Test points
Resistor based Uses the internal reference resistors in the verification equipment. The reference resistor values can be measured with a high accuracy ohmmeter and entered in the software programme. The program automatically converts the resistor values into the corresponding temperatures according to IEC751. Resistor based principle is also used when forward and return temperatures are simulated with decade boxes. In this situation the wires from the decade boxes must be connected to the terminals 5 - 6 and 7 - 8 after disconnecting the wires for the internal resistors. Note The resistors are measured at Danfoss in Denmark with traceability to the Danish national standards for electrical, resistance. For some countries verification is only valid when the equipment used is traceable to the national standards of this country. In this case the resistors must be calibrated locally with the required traceability.
Temperature based This mode is used when verification of the energy calculator including temperature sensors is required. For this purpose a temperature difference must be established by means of two temperature controlled, well stirred liquid baths. The reference temperature measured in °C for forward/return by a thermometer (working reference). The deviation in read values and true temperature (measured by the laboratory reference). Thermometer can be entered with sign. From the factory the deviation value is set default to 0 °C for T1, T2 and T3.
6.1.3 Verification
No stops Test are carried out without any stop between the test points T1, T2 and T3. Intermediate stops Test are carried out at the 3 test points. This allows time for changing the set points of temperature baths and temperature stabilization or changing the setting of the decade resistor boxes simulating the return and forward temperature. After stabilizing the forward and return temperatures measured by the working reference, these temperatures must be entered into the folder "verification". A stabilization time in the baths, can be entered in order to temperature stabilize the sensor before measuring. A dialog box appears when the sensors can be moved to the next bath.
6.1.4 Heat coefficients
Auto calculate The heat coefficients are automatically calculated depending on the true temperature in forward and return for T1, T2 and T3. The calculation is based on the algoritm found in the "Tabels and coefficient for water as heatconveying liquid. ã 1986 by Wirtschaftverlag NW, ISBN 3-88314-522-X"
Manual insert The heat coefficients can be entered manually based on local recommendation. Whenever changing heat coefficient manually, a password must be entered. 6.2. Passwords
In order to change any verification data, a password must be entered - followed by an "Apply" in the PC software. Following passwords have been default selected: Change of modes for test points, heat coefficients and verification: Write "Setup" under the window "Verification data". Change of verifications data: Write "danfoss".
6
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
6.3. Change of parameters under "Verification data"
Before change of preset values for heat coefficients, integration time and permissible errors, a password must be entered.
Integration time is preset from Danfoss and effect the uncertainty of the calibration/ verfication. Danfoss recommend the following preset values:
3°K < DQ £ 10K: Minimum 30 sec. 10°K < DQ £ 15K: Minimum 10 sec. Minimum 5 sec. 15°K < DQ: The influence of integration time can be studied in details in chapter: "Calculation of measurement uncertainty". 6.4. Verification
After having checked the folder: "Verification data" is correct, - switch to the folder "Verification". In the folder "Verification" all data referring to the INFOCAL 5 (device under test) can be entered. a
Type: Build-up number of the unit.
b
Serial No.: Enter the serial number of INFOCAL 5.
c
Identify field: Possibility for customer name, calibration operator and approved signatory.
d
Comment field: Ex with metrological data, room temperature, humidity, pressure, instrument data, reference manuals etc.
The INFOCAL 5 is now ready for calibration/verification. Start the verification by entering "Start verification". A progress line indicates the status of the program. Note If selected verification "one at the time" a dialog box will appear indication when it is time to move the forward sensors to the next temperature bath or change the resistor value in the decade boxes.
DKFD.PS.022.H2.02
7
INFOCAL 5 Verificator
6.5. Test data
When the test have been completed, the results will be displayed on the screen and followed by a message "INFOCAL 5 accepted" or "INFOCAL 5 not accepted", based on the limits MPE (Maximal Permissible Errors).
6.6. Storing of data
If the verification is accepted (lower than MPE values) the data can be stored by a click on "File" and then "Save verification file". The file can be retrieved by "Open verification file".
6.7 Certificate
Results of verification can be printed by a click on the botton: "certificate".
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Certificate No.:
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T1 T2 T3
53.395 68.88 159.837
49.997 49.997 15.011
4.1309 4.1341 4.2173
0.12 0.04 0.02
0.00047 0.00087 0.00339
0.00047 0.00087 0.00339
-0.523 -0.193 -0.018
1.36 0.66 0.5
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Verified by: _____________
Date: ___________
Approved signatory: _____________
.../continued 8
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
Important If the base part contains a 230 V AC supply or 24 V AC supply, it is important to wait min. 20 sec. or until the display segments have disappeared in the display, before connecting top and base part! For battery versions, connections of top and base part can take place without any waiting time. 7.
Calibration routine
The verification equipment has very long-term stable resistance references. Under normal conditions these require just calibration once a year or whenever moving the verification equipment to another locality. During calibration use an accurate precision ohmmeter with 4 wire measuring principle and traceable calibration.
Before starting calibration routine disconnect the cable to the COM port in the PC and briefly disconnect the 230 V supply in order to reset activated relays on the printed circuit board. 1. Turn on the power to the verification equipment. Disconnect the red wires from terminal 5 & 6 and the blue wires from terminal 7 & 8.
Verfication mode: Jumper:
off
on
12 V AC
Flow pulse wire to terminal 10 Jumper J4 Jumper J3 Jumper J2
3 wire cable to PC
Jumper J1
The cable to the computer has the following colours: TX: yellow, RX: green, GND: white. 12 V power terminal requires 12 V AC and have no polarisation.
DKFD.PS.022.H2.02
9
INFOCAL 5 Verificator
2. Connect the red wires (5 & 6) to the calibration ohmmeter. Move jumper J1 to the "On" position. Relay RL 1 is active. Make a note of the measured T1forward (approx. 603 ohm). Connect the blue (7 & 8) wires to the calibration ohmmeter. Make a note of the measured T1return (approx. 597 ohm). Move jumper J1 back in position. 3. Connect the red wires (5 & 6) to the calibration ohmmeter. Move jumper J2 to the "On" position . Relay RL 2 is active. Make a note of the measured T2forward (approx. 633 ohm). Connect the blue (7 & 8) wires to the calibration ohmmeter. Make a note of the measured T2return (approx. 597 ohm). Move jumper J2 back in position. 4. Connect the red wires (5 & 6) to the calibration ohmmeter. Move jumper J4 to the "On" position. Relay RL 4 is active. Make a note of the measured T3forward (approx. 805 ohm). Connect the blue (7 & 8) wires to the calibration ohmmeter. Make a note of the measured T3return (approx. 529 ohm). Move jumper J4 back in position. 5. Make sure that all the four jumpers are in the "Off" position. After the new resistance values and heat coefficients are entered "Apply" must be entered. Note If the mode "automatic calculation" in setup mode is chosen, the heat coefficients are automatically updated. The verification equipment is now ready for use. The three values for Tf and the three values for Tr are automatically generated based on the following formula: RT = R0 (1 + A x T + B x T2) R0 = resistance at 0 °C, Pt 500: = 500 W A = 0.0039083 °C-1 B = -0.5775 x 10-6 °C-2 T can be calculated from the resistance as follows:
7=
− ( 50 × $) + ( 50 × $) 2 − 4 × 50 × % × ( 50 − 57 ) 2 × 50 × %
The above relations are according to IEC751.
10
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
8.
Integration time (measuring time)
As the INFOCAL 5 is placed in the basepart, the INFOCAL 5 is automatically set into a verification mode and the "heart beat" indicator on the display indicates that the INFOCAL 5 now is in the verification mode. The INFOCAL 5 now integrates every second. This means that the INFOCAL 5 will measure the forward and return temperatures, the volume pulses and increase the accumulated energy value every second. As the integration time influences the variance of the accumulated energy in a test point, we must consider this in the selection of integration time at the different test points. Further more the natural repeatability is better with high temperature differences. These considerations are explained more in details in the paragraph "Calculation of measurement uncertainty". As default Danfoss have the factory settings: Integration time T1: 30 sec. T2: 10 sec. T3: 5 sec. and Danfoss recommend not to change these setting as it will affect the measuring stability. These integration result in the overall measurement uncertainty of: T1 = 0,63% T2 = 0,17% T3 = 0,039% See the next chapter for detailed description.
9.
Calculation of measurement uncertainty
The calculation below of the measurement uncertainty of the equipment partly depends on the frequency with which the equipment is calibrated. The calculation therefore is only intended as a guide. The calculations are based on EAL-R2, April 1997, "Expression of the Uncertainty of measurement in Calibrations" and GUM "Guide to expression of Uncertainties in Measurements". To calculate the best measurement capability, you must calculate the uncertainty for each of the uncertainty components as a standard deviation before adding them up according to the rules of adding up standard deviations for normal distribution/Gaussian distribution. If the distribution of the uncertainty component is not the normal distribution/Gaussian distribution, the standard deviation must be calculated on the basis of your knowledge of the distribution type as well as upper and lower limit +a, -a (e.g. factory specifications and experience notorious values). Especially for the rectangular distribution used in this case, the standard uncertainty is calculated as a/Ö3.
Step by step guide · Calculate the standard deviation for each uncertainty component. · Square to convert to (statistical) variance. · Simply add up to find the total variance. · Calculate the 1-sigma measurement uncertainty as the square root of the total variance. · Multiply by 2 (coverage factor k = 2) to calculate the best measurement capability. To this you must add the measurement uncertainty from the calibration of the reference resistances. Finally, to reach the total measurement uncertainty, you have to add the natural variance of the energy calculator readout at each test point.
DKFD.PS.022.H2.02
11
INFOCAL 5 Verificator
9.1 Assumptions for the calculation
The basis of the calculation is the energy calculation formula:
( = 9 × ∆Θ × N 6WXFN where E = energy V = volume DQ = temperature difference Tforward - Treturn k Stuck = heat coefficient To ascertain the uncertainty of the simulated energy, E, you have to determine the uncertainty (standard deviation) of each element on the right side in the formula. Volume, V, has the uncertainty 0 as the energy calculator is always stimulated by a precise number of (volume) pulses. The temperature difference, DQ, is influenced by the uncertainty of the two resistances simulating forward and return temperatures. These are influenced by variations in ambient temperature, the stability of the resistances and the calibration. The heat coefficient, kStuck, is associated with no uncertainty. In other words, only the uncertainty of the resistances determines the best measurement capability of the simulated energy, E. The resistances (Wishay S102C) have the following characteristics:
Temperature coefficient: ±1.2 ppm/°K Stability: ±25 ppm/year The calibration of the resistances only contributes with the short-term stability and the linearity of the reference ohmmeter. The absolute accuracy is not that important as it does not contribute to any measurement uncertainty for the temperature difference, DQ, simulated by Tforward and Treturn. The estimated effect per resistance is approx. 4 ppm. The equipment is expected to be calibrated with an uncertainty ±10 ppm at 23 °C ±1 °C at least once a year. Expected ambient temperature is 23 °C ±5 °C when using the verification equipment.
12
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
Uncertainty calculation for test point T1
Tforward = 53.5 °C corresponding to Rforward = 603.721 W Treturn = 50 °C corresponding to R return = 596.986 W DQ = 3.5K T return Temp. Stab. T forward Temp. Stab. Calibration
596.986 W x 1.2 x 10-6/K x 5 °C/Ö3 = 2.1 mW ~ 0,0011K 596.986 W x 25 ppm/year x 1 year/Ö3 = 8.6 mW ~ 0,0045K
s2 = 1.21 x 10-6 [K2] s2 = 20.3 x 10-6 [K2]
603.721 W x 1.2 x 10-6/K x 5 °C/Ö3 = 2.1 mW ~ 0,0011K 603.721 W x 25 ppm/year x 1 year/Ö3 = 8.7 mW ~ 0,0045K 2 x 600 W x 4 x 10 -6/Ö3 = 2.8 mW ~ 0.0014K
s2 = 1.21 x 10-6 [K2] s2 = 20.3 x 10-6 [K2] s2 = 1.96 x 10-6 [K2] Ss2 = 45.0 x 10-6 [K2] s = 0.0067 [K] 0.0134 [K]
Measuring uncertainty of 1 x std. dev. level Best measurement capability (expanded measurement uncertainty, k = 2)
The best relative measurement capability at DQ = 3K thus is 0.0134/3 x 100% = 0.45% The best measurement capability expresses the measurement uncertainty of the verification equipment at T1. To this you will have to add the measuring uncertainty of the energy calculator i.e. the repeatability to obtain the total measurement uncertainty of the calibration at T1. Tests have shown that the INFOCAL 5 has a repeatability of 1.21% on single measurements of DQ. If at T1 the verification includes n temperature integrations, the accumulated energy will be distributed with a repeatability of 1.21%/Ön. If at T1 30 integrations are selected, the energy calculator will contribute with 1.21%/Ö30 = 0.22%. The combined measuring uncertainty thus is:
8 =
( 0 .45 %) 2 + ( 2 × 0 .22 %) 2 = 0 .63 % (k = 2)
DKFD.PS.022.H2.02
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INFOCAL 5 Verificator
Uncertainty calculation for test point T2
Tforward = 69 °C corresponding to Rforward = 633.462 W Treturn = 50 °C corresponding to Rreturn = 596.986 W DQ = 19K T return Temp. Stab. T forward Temp. Stab. Calibration
596.986 W x 1.2 x10-6/K x 5 °C/Ö3 = 2.1 mW ~ 0.0011K 596.986 W x 25 ppm/year x 1year/Ö3 = 8.6 mW ~ 0.0045K
s2 = 1.21 x 10-6 [K 2] s2 = 20.3 x 10-6 [K 2]
633.462 W x 1.2 x 10-6/K x 5 °C/Ö3 = 2.2 mW ~ 0.0011K 633.462 W x 25 ppm/year x 1year/Ö3 = 9.2 mW ~ 0.0048K (597 W + 633 W) x 4 x 10-6 /Ö3 = 2.8 mW ~ 0.0014K
s2 = 1.21 x 10-6 [K 2] s2 = 23.0 x 10-6 [K 2] s2 = 1.96 x 10-6 [K 2] Ss2 = 47.7 x 10-6 [K2] s = 0.0069 [K] 0.0138 [K]
Measuring uncertainty of 1 x std.dev. level Best measurement capability (expanded measurement uncertainty, k = 2)
The best relative measurement capability at DQ = 19K thus is 0.0138/19 x 100% = 0.072% The best measurement capability expresses the measurement uncertainty of the verification equipment at T2. To this you will have to add the measuring uncertainty of the energy calculator i.e. the repeatability to obtain the total measurement uncertainty of the calibration at T2. Tests have shown that the INFOCAL 5 has a repeatability of 0.24% on single measurements of DQ. If at T2 the verification includes n temperature integrations, the accumulated energy will be distributed with a repeatability of 0.24%/Ön. If at T2 10 integrations are selected, the energy calculator will contribute with 0.24%/Ö10 = 0.076%. The combined measuring uncertainty thus is:
8 = (0.072%) 2 + ( 2 × 0.076%) 2 = 0.17% (k = 2)
14
DKFD.PS.022.H2.02
INFOCAL 5 Verificator
Uncertainty calculation for test point T3
Tforward = 160 °C corresponding to R forward = 805.272 W Treturn = 15 °C corresponding to Rreturn = 529.247 W DQ = 145K T return Temp. Stab. T forward Temp. Stab. Calibration
529.247 W x 1.2 x 10-6/K x 5°C/Ö3 = 1.8 mW ~ 0.0010K 529.247 W x 25 ppm/year x 1year/Ö3 = 7.6 mW ~ 0.0040K
s2 = 0.91 x 10-6 [K2] s2 = 15.8 x 10-6 [K2]
805.272 W x 1.2 x 10-6/K x 5°C/Ö3 = 2.8 mW ~ 0.0015K 805.272 W x 25 ppm/year x 1 year/Ö3 = 11.6 mW ~ 0.0060K (529 W + 805 W) x 4 x 10-6/Ö3 = 3.1 mW ~ 0.0016K
s2 = 2.10 x 10-6 [K2] s2 = 36.5 x 10-6 [K2] s2 = 2.57 x 10-6 [K2] Ss2 = 57.9 x 10-6 [K2] s = 0.0076 [K] 0.0152 [K]
Measuring uncertainty of 1 x std. dev. level Best measurement capability (expanded measurement uncertainty, k = 2)
The relative measuring ability at DQ = 145K thus is 0.0152/145 x 100% = 0.010% The best measurement capability expresses the measurement uncertainty of the verification equipment at T3. To this you will have to add the measuring uncertainty of the energy calculator i.e. the repeatability to obtain the total measurement uncertainty of the calibration at T3. Tests have shown that the INFOCAL 5 has a repeatability of 0.04% on single measurements of DQ. If at T3 the verification includes n temperature integrations, the accumulated energy will be distributed with a repeatability of 0.04%/Ön. If at T3 5 integrations are selected, the energy calculator will contribute with 0.04%/Ö5 = 0.018%. The combined measuring uncertainty thus is:
8 = (0.0152%) 2 + (2 × 0.018%) 2 = 0.039% (k = 2) 10. Possible improvements/adjustments of the measurement uncertainty
The stability of the resistances contributes most to the measurement uncertainty. A more frequent calibration will reduce the drift between two calibrations and thus also reduce this component. From experience we know that the stability will be even better than specified by Wishay. After a period of 1 - 2 years the stability typically will be 10 - 15 ppm/year. When experience with the stability of resistances is obtained, it can be incorporated in the uncertainty calculation thus contributing to a smaller measurement uncertainty. Also when increasing the number of integrations the measurement uncertainty can be reduced. An increased number of integrations, however, means a longer verification time. As a rule-of-thumb you must choose the number of integrations so that the uncertainty contributed by the energy calculator equals the best measurement capability of the verification equipment at the test point.
DKFD.PS.022.H2.02
15
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521H1089
DKFD.PS.022.H2.02
ã Danfoss A/S (FD-SJ/KN/SSS&GBIN/KH) 06.2001 P65
