- Initial inspection, before calibration state
- Calibration procedure
- Performance verification
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Almost every electronic measurement device needs calibration to adjust internal offsets and errors to minimum. This procedure is done during manufacturing, but sometimes there is need for additional calibration on end-user site, for example after repair. Calibration usually requires at least twice better accuracy “standard” for reference, so it’s often rather troublesome without having gear and knowledge. Almost all instrument vendors provide calibration service, but if your have proper gear in lab – calibration can be performed at spot.
Fluke service manual with calibration procedure. Fluke recommends 5700A calibrator which cost many many thousands dollars, but it’s not the only way to calibrate these temperature meters. We will use calibrated “poor-man” DC standard, EDC MV106 for this task.
Initial inspection, “before calibration” state
On right side – ADC calibration fixture (two-copper terminal jack made from two thermocouple T jacks).
Cal sticker is tampered.
-82°C with tested K-type thermocouple hanging in +25C room temp ain’t right.
Closeup for connector used for voltage source (EDC MV106 DC standard calibrated to Keithley 2001 with Tek cal 5.FEB.2014) connection to Fluke 52-2 inputs.
I used copper wire from UTP LAN cable, to have direct copper connection and minimize thermal EMF.
0.0000v set – meter shows 20-30C…
Calibration A-D convertor by providing 80.0000mV and -8.00000mV to inputs.
-8.00000mV read as -7996.9 uV, which is in range for calibration requirements of –7995.0 to –8005.0.
Calibration reference point:
REF point offset is 3.8C.
After corrected offset:
“After calibration” Performance test values (K-Type Thermocouple) with icebath.
Channel 1 on left, channel 2 on right:
1. 0.0000 mVDC / 0.0 °C
2. 0.9193 mVDC / 23.0 °C
3. -5.7297 mVDC / -190.0 °C
4. 40.8853 mVDC / 990.0 °C
5. 48.8382 mVDC / 1200 °C
Same K-type probe reads correct +25.6°C now.
That’s it, job done.
Calibrated Keithley 2001 Multimeter (5.FEB.2014)
Keithley 2002 Multimeter (10.APR.2007)
Calibrated EDC MV106 DC Voltage standard +-30ppm/°C (8.FEB.2014)
Calibrated Keithley 2400 Sourcemeter (14.JAN.2014)