Author Topic: Quadtech 1880 Milliohm eter calibration procedure  (Read 119 times)

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Offline HalFoster

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Quadtech 1880 Milliohm eter calibration procedure
« on: August 12, 2019, 03:06:49 pm »
I have a Quadtech 1880 milliohm meter that I would like to calibrate but I can find nothing out online as to the exact procedure.

So far, it seems to be:

1)  Turn unit on
2)  Move calibration switch to enable position
3)  Unit shows "0", short probes and press the "Man/Ext" key - unit does call.
4)  Press "Man/Ext" again, unit shows required reference value.  Connect to probes, press "Man/Ext" - unit does cal
5)  Continue steps 3 & 4 through 1.9M range; unit resets.
6)  Move calibration switch to disabled.
7)  Cycle power, done.

What is happening is that after this, meter only reads somewhat correctly if the measured value (1st digit) is in the lower part of the current range.  A value of 1.5 milliohms, 1.5 ohms, 1.5 K or 1.5M measures correctly; values of 4 milliohms, 4 K, 6 milliohms cause erratic readings.

Question is, it this due to a bad cal or are there hardware issues with the meter.  If I knew for sure the exact calibration procedure, it would at least help me to know where to start troubleshooting.



Online Kleinstein

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #1 on: August 12, 2019, 05:13:14 pm »
This sound a bit like a hardware problem, like a wrong current source causing the source to drive into saturation.

With a militohm meter, I would suggest using 4 wire technique. So the short may be not just connecting 2 wires. Or closing Kelvin probes together. There are special 4 way shorts. Other wise the sens wires should be connected, the drive wire should be connected and some wire / resistance between the 2 pairs.

Online Shock

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #2 on: August 12, 2019, 05:35:02 pm »
Contact distributors or manufacturers for the schematic, service manual and calibration info whatever they can provide. Manufacturers often include test points or short points to confirm the test equipment agrees with itself and is operating correctly.

You mentioned erratic measurements, does this mean reproducible fluctuating measurements or reproducible inaccurate measurements? There is a big difference between the two.

Are you using the original kelvin leads sold with the device as it may be similar to my micro ohm meter which has two 100k resistors between each drive and sense.

First you must rule out the components under test to ensure they are not complicit in the inaccuracies, then if it's not try and include offsets in your calibration to see which way the inaccuracies swing. You might be able to characterize where it is occurring. Obviously you should be able to produce reproducible measurements regardless of accuracy or drift in ranges.

Probably about that time you might want to scope the calibration procedure and during normal measurements to see what is different. Also you can verify the power supply noise/ripple and general component quality. Normal warnings about connecting the scope ground clip to a circuit that is not isolated/floating or at ground potential apply.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM
Oscilloscopes: Rigol DS1054Z, Phillips PM3065

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