Author Topic: Quadtech 1880 Milliohm eter calibration procedure  (Read 3153 times)

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Offline HalFosterTopic starter

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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.

TIA,

Hal
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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.
 

Offline 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.
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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #3 on: January 08, 2021, 08:13:53 am »
HI there, I was wondering what happened with the issue you were having with your quadtech 1880?
I just got one and it seems it is not reading anything. I zero it out. but it keeps reading the same values (-.5522 to -.5421) no mater what is connected to it.
where you able to find any schematics or a service manual for it?
 

Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #4 on: January 08, 2021, 08:18:29 am »
This is what I have for the 1880. Mine works great btw  :)

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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #5 on: January 08, 2021, 09:47:22 pm »
thank you for your reply,
I have those manuals . they are basically the user manual and the brochure. I need the service manual if it exists with schematics and or pictures of the big flat board inside.
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #6 on: January 08, 2021, 10:26:28 pm »

Sorry again, I am just figuring out this blog. I was replying to your massage in a different way. so you may have several reply.
I have the manual and brochure.
I need either the schematics or a few pictures of the board setting flat in the unit.
on mine it looks like someone had modified it for their use.
there are 2 snipped wiring of 5 wiring that extent from the rear of the test lead connector to the board. snipped off wiring connect to the right of the connector on a couple of diodes. and a few resisters around the board looks like done after the manufacturing. I could send you pictures if you want.
I  need pictures of a good unit please.

thank you
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #7 on: January 08, 2021, 10:30:12 pm »
you ever got that quadtech 1880 calibrated and working?
 

Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #8 on: January 09, 2021, 03:07:57 am »
Sounds like your unit is the same as mine internally and was a 'factory bodge'  :palm: These photos should be easy to compare against yours for a start. I will leave the top off mine for a couple of days if you want any voltages measured or photos elsewhere on the board.  :)

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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #9 on: January 10, 2021, 04:47:38 am »
If you wouldn't mind can you please take pictures of all around that board please and send to me. Pictures you sent looks the same as mine so far. On mine there is a few more places that look bodged.
 

Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #10 on: January 10, 2021, 05:03:16 am »
Overall and three separate ones for a bit more detail. The tight hold on a service manual and calibration service for these now older models is complete  :bullshit: time they pulled their heads out of their ....

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Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #11 on: January 10, 2021, 05:03:53 am »
part 2
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Offline HalFosterTopic starter

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #12 on: January 10, 2021, 09:04:16 am »
Still no luck on the correct procedure by me.  Mine has/had the same bodge (I changed the connector to a standard DIN to facilitate making new test cables) -  I had been wondering if that was factory or not.

Hal
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Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #13 on: January 10, 2021, 09:10:38 am »
The bit of recent trawling I did indicates the use of a custom 0.019. 0.19. 1.9  \$\Omega\$ set etc for $2k+ I have also looked and searched in the past for the Original Manufacturer "Chen Hwa Tek" with no success. Chroma the now brand owner seem to want to tie the units to return to them only so they can gouge you for $ instead of helping with an older model.  :--
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Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #14 on: January 11, 2021, 01:45:55 am »
Naked Bum shot for BobbeBob of the front panel PCB connection area.

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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #15 on: January 11, 2021, 04:51:11 am »
Thank you. I took some smaller pictures Hopeful these will make it through.
would you mind taking more pictures from the back as many as you can please.

thank you

kind Regards
Bob
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #16 on: January 11, 2021, 04:55:26 am »
more pics of the mine, modified one.
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #17 on: January 11, 2021, 04:57:07 am »
more pics of the modified one
 

Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #18 on: January 11, 2021, 05:06:20 am »
Interesting Bodge  :-\ Across the large Pad R26 where mine has the 1 \$\Omega\$ 10W resistor on the chassis with wires going to it yours has what looks like a 1/4W resistor? What is the value on it might give a clue as to what some of the other bodges were setting out to achieve  :-//
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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #19 on: January 11, 2021, 05:08:56 am »
you got to see the bodge work on mine. I sent a bunch of pictures. the real mess is in the rear.
I was planning to remove all the add on component and fix the cut traces to see what happens.  I will leave the ones that match Beanflying boards.
just waiting for a few more pics.
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #20 on: January 11, 2021, 05:10:45 am »
The value seems to be 100K,
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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #21 on: January 11, 2021, 05:12:47 am »
Or is it 1m ohm?
 

Offline beanflying

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #22 on: January 11, 2021, 05:18:22 am »
1 Meg \$\Omega\$. Without tracing the circuit out or trying to sort out your rats nest from photos at a very rough guess they were trying to reduce the test current or change the range able to be tested by the unit while maybe making use of its tolerance/sorting functionality?  :-//
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Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #23 on: January 11, 2021, 05:43:23 am »
I just double checked. it is a 100K.
I figured I will just remove everything they added and reconnect the traces, Add the same resister you have on yours. if I see signs of hope, them will think of calibration.
I am open to suggestions thought.
 

Offline BobBeBob

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Re: Quadtech 1880 Milliohm eter calibration procedure
« Reply #24 on: January 12, 2021, 07:54:31 am »
Hi, I was wondering if it is not too much trouble for you, at you convenience, Please send some more picture of the back side of the PCB. I need enough pictures to be able to see the entire PCB back side. please.

thank you

regards

Bob B
 


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