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Old 4th August 2009, 01:14 AM   #1
gto127 is offline gto127  United States
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Default How to calibrate Fluke 87 meter?

I have a 20 year old Fluke 87 meter that I feel may need calibrating due to age and due to some different measorements with milivolts compared to my scope. I'm tight on money now so I can't send it to Fluke. Could anyone tell me how to cal this thing?
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Old 4th August 2009, 01:48 AM   #2
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The easiest way is to compare it against a meter you know is a good. I have an old Fluke 75 meter and have burned out the fuse resistor twice so far. Its only a few millivolts off from the calibrated HP 34401 meters at work. Do you know anyone with access to calibrated equipment?

DMMs will start to disagree with a scope when the sinewave has distortion or stops being a sine. Frequency response plays a big part in this too.
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Old 4th August 2009, 02:04 AM   #3
gto127 is offline gto127  United States
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Thanks for reply. I don't know anyone with calibarted equip. I live in a small town. Mabye it is in spec It could be the wave forms like you said. I do have a agilent power supply which is supposed to be a very high end supply. Could this be accurate enough to do a cal or would it vary like most everything else?
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Old 4th August 2009, 02:07 AM   #4
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If you don't have access to calibrated equipment your best bet will be to calibrate to a band gap reference or failing that the Vf on an LED. If you averaged a green, red & yellow LED I dare say you'd be within 5%.

Or are you looking to calibrate the 500V scale?

AC is a different matter of course, as astouffer mentions.

I think you can do everything with a good volt reference. Anyone know other good references? What where those battery cells they used to use before NIST?
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Old 4th August 2009, 02:08 AM   #5
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BTW, I'd trust the old Fluke over everything else you mentioned. My experience with Fluke is that they are very stable.

Scopes & PSUs.........hmmm

edit: it came to me: lelanche
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Old 4th August 2009, 02:51 AM   #6
gto127 is offline gto127  United States
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I was looking to cal the milivolts mainly. I'm doing tracking & focus servo adjustments on old cd players. Of course I use the scope for most of it but some measurements require a DVM. How to you use the LEDS to cal the meter?Measureing voltage across?
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Old 4th August 2009, 03:03 AM   #7
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exactly.
The forward volt drop on an LED is very stable and consistent. That's why it make such a good reference for current sources. Don't want to quote voltages from memory because i'd be wrong but they're all in the 1-2V range (except blue of course)

Knowing the rms behaviour of your meter you could use this to calibrate AC volts also.
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Old 4th August 2009, 03:54 AM   #8
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You can buy a reference grade voltage reference like an LM4030, LM4132, MAX6033, REF5010, etc. But even those are typically 0.01% at best and your Fluke is supposed to be more accurate than that. I have a high-end Agilent bench DMM with a 4 figure price tag that's still under factory calibration and reads to 7 digits. But my ancient Fluke 87 agrees closely enough with it for 99% of anything I need to measure. And the Fluke has been dropped more times than I can count. So, unless you have reason to believe your Fluke is wrong, I'd just trust it.
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Old 4th August 2009, 03:56 AM   #9
gto127 is offline gto127  United States
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Thanks its good to know there is a component that is consistant in vout. Even voltage regulators tend to vary in v out slightly from each other.
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Old 4th August 2009, 04:05 AM   #10
gto127 is offline gto127  United States
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To Rocket scientist I was thinking there might be a problem due to some measurements i was taking the other day in the 350-400mv ranfge. The volt kept disapearing around 360mv & up. It could have been just an unstable source but I was just thinking meter may have been out of cal & I was actually in a higher volt range with source causing it to be unstable..
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