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Posted to sci.electronics.design,sci.electronics.repair,sci.electronics.equipment
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Calibration Of Electronic Equipment In The Home Workshop
Jim Yanik wrote:
Robert Baer wrote in
news
clifto wrote:
Jim Yanik wrote:
After reading all this,I checked the $3 DMM I bought at a Harbor
Freight sidewalk sale,and it turns out the *input Z is only ONE
megohm*. YUK!
My first meter cost five times that, was analog, and only had 20K
ohms per volt.
For those young folk who aren't familiar with that, yes, the meter
input impedance changed depending on the range you set the meter to.
Check; the neatthing is that on higher voltage scales, the input
resistance exceeds that of a DMM.
Which is why i built a voltmeter/currentmeter around a 5 microamp
movement giving 200K per volt sensitivity.
Then there's the Fluke differential voltmeters,that have nearly infinite
impedance at null. ISTR a HP diff VM that had a 100Meg Z on it's off-null
mode.Then there are Keithley hi-Z meters,with gigohm input Zs.
Wouldn't be neat to have a handheld differential voltmeter?
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