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Mastech multimeter mod
Mastech multimeter mod
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Old 3rd January 2014, 01:35 PM   #1
umut1001 is offline umut1001  Europe
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Default Mastech multimeter mod

Hello
I have Mastech MS8222H multimeter.I usually match some 10nf and 100nf capacitors with this.But the values changes by room temperature.Can i make any modification by changing resistors in it?(I have some 5ppm leaded resistors)Can i modify this and make it a better multimeter?
I do not know how it works when measuring film caps.Maybe it works like a RC circuit right?
Thanks
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Old 3rd January 2014, 01:51 PM   #2
doctordata is online now doctordata  Australia
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Mastech multimeter mod
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Originally Posted by umut1001 View Post
Hello
I have Mastech MS8222H multimeter.I usually match some 10nf and 100nf capacitors with this.But the values changes by room temperature.Can i make any modification by changing resistors in it?(I have some 5ppm leaded resistors)Can i modify this and make it a better multimeter?
I do not know how it works when measuring film caps.Maybe it works like a RC circuit right?
Thanks
Have the same problem here , ( was 40C today , tomorrow 43C)
Easy to solve , buy an accurate thermometer and measure at 20 degrees C
Have a big airco in my room and set it on 20 and wait .
Your capacitors wont have the same capacity with different temperatures . Have a look at the datasheet of your capacitors and look at the thermal specs .
The problem is probably not in your multimeter .

Cheers ,

Rens
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Old 3rd January 2014, 02:21 PM   #3
umut1001 is offline umut1001  Europe
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-Hehe.Another part of the world.It is around 10C here.Let us make a tunnel between your room and my room
The caps are mkp1837 and kp1830.
for mkp1837 temp coeff is - 250°C x 10-6/°C (typical value)
When i measure by multimeter in cold it is 102 nf and in hot it is 100nf.The difference is around 20celcius degree.So it makes around 0,5% difference in capacitor
But in total measurement it makes 2% difference.Regards
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Old 3rd January 2014, 03:42 PM   #4
multisync is offline multisync  Canada
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is it the multimeter that's drifting or the capacitors or both? Put the meter in a fridge. wait a couple of hours. Take your capacitor readings. Is there any difference in the capacitor reading with the meter in the fridge or the meter outside at ambient. Remember your circuit will be in some kind of a box which will be heated by the air and any components inside. Where will the final project be?
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Old 3rd January 2014, 05:36 PM   #5
umut1001 is offline umut1001  Europe
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I have an infrared heater in my office.I put multimeter in front of it and wait about 30 minutes.After this i measured capacitor(capacitor temp is same)And it was 101nF when multimeter was cold and 97,4nf when multimeter was hot.
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Old 4th January 2014, 03:19 PM   #6
multisync is offline multisync  Canada
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Good, so you know that the reading of the multimeter drifts up with temp. Now keep the teperature of the meter constant and heat the capacitor. How much does it change. What will be the final circuit that uses the capacitors and how critical is the value. ie frequency shaping or coupling or bypass. How hot will it get in your enclosure.
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Old 4th January 2014, 03:57 PM   #7
Samuel Groner is offline Samuel Groner  Switzerland
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You say you use it for matching--so the absolute uncertainity is entirely uncritical. What counts is how stable the reading is between two measurements; as this is done within a few seconds, perhaps minutes, the meter is unlikely to drift significantly.

Samuel
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Old 4th January 2014, 04:43 PM   #8
umut1001 is offline umut1001  Europe
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Hi.Some customers want 100nF capacitor +-1% matched.
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Old 4th January 2014, 05:15 PM   #9
Samuel Groner is offline Samuel Groner  Switzerland
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Originally Posted by umut1001 View Post
Some customers want 100 nF capacitor +-1% matched.
You get a 3.6% drift for maybe a 30° temperature rise (perhaps more). So you can expect less than 0.36% drift if you keep the temperature of your meter within 3°. This should not be too difficult if you shield it from direct heat/airflow, and allow sufficient time for warmup.

If that's not good enough we'd need to see a schematic of the meter for an educated guess. Perhaps it's easier to derive a dedicated jig for capacitance measurement.

Samuel
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Old 4th January 2014, 05:26 PM   #10
Rundmaus is offline Rundmaus  Germany
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I think a dedicated bridge circuit with a low-tolerance set of reference parts would be a better approach.

Rundmaus
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