This thread is to start and discuss methods and various measurement/validation procedures that apply to commercial instruments temperature coefficient specification.
This thread is draft work in progressWe do invite any participants/company representatives and metrology experts to chime in
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Based on discussion with
Dr.Frank started first
here about 3458A's temperature stability of main 10V DC range.
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I have verified TC of 10V range on two HP 3458A meters, not three (yet).
Third meter awaiting new A3 (3458 "C") and forth and latest one has stable A3, but not tested in any details yet (awaiting front panel/new terminal block parts, that is meter "D" in my terms). I do NOT say that all 3458A should be this low tempco, just merely stating data I get.
Background info:
All details about 3458A STD meter.. This unit have
Agilent A3 from 2014 with Elantec comparator patch board due to EOL of original DIP comparators.
A9 here is STD, but with LTZ1000
CH chip, since original ACH was a jumper. A9 is modified with 100K BMF for lower oven temp.
All details about 3458 "B" meter. This unit have
brand new A3 ADC from 2016 with modern ALTERA CPLD instead of Fujitsu gate array.
A9 here is also STD. A9 is modified with 100K BMF VAR for lower oven temp.
I also did minor fix-ups last year covered in short vid:
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Please note, i use simple box method for tempco calculation, not the more complete discrete math.
As example - measure constant 10V by meter at ambient (or TEMP? reading) at Tlow as 0.0 ppm reference. Then ambient change by significant amount (e.g. +10C), wait till reading settle again - record result as Thigh = 1.0 ppm. Calculate meter 10V range TC as Tlow - Thigh / DeltaT , in this theoretical example 0.0 - 1.0 / 10 = 0.1 ppm/K. But i do always log all thousands of samples during temperature variation to see correlation (or lack of) between readings and temperature, as example data below shows too.
Same method I use to calculate all my tempco (for resistors, meters, references, etc), only difference if it's DUT that subject to temperature change (we keep ambient stable for this), or the meter (we keep measured standard isothermal).
Dr. Frank, I found data plot with 3458A and 3458B meter data.
10V DC range*
First test run, using two KX LTZREF at constant +24.00 temperature. Test with 3458A and 3458B. Each meter measure different KX REF.
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Another test run, using FX #3 LTZ1000A reference at constant +37.00 temperature. This time with 3458A, 3458B and one of K2002's. All three meters measure same LTZ.
OHMF Resistance 4W ranges*
Test with 3458A,3458B,2002-4,2002-6 meters. Each meter measure own 4-wire resistor (hermetic VHP BMF) in isothermal box
You can download CSV raw data for any analysis or processing.
Data format header:
date;hp3458a;dmm2;temp;temp2;ext_temp;rh;pressure;rtd_temp;tec_curr;
HP3458A is hp3458a column,
dmm2 is 3458B unit data.
temp is HP3458A's TEMP? output value
temp2 for second meter
ext_temp, rh, pressure columns are readback from BME280
rtd_temp is feedback temperature of Honeywell HEL-705 PT100 sensor, mounted to small enclosed die cast metal chamber with
two different LTZ KX references. This reading is PID input of Keithley 2510, used to control 40W TEC to maintain reading +/-0.005c.
tec_curr is drive current to the TEC element.