I have an old cie 7905A multimeter. When I measure a dc voltage it gives me a value. If I permute the + and - leads I read another value, some % different. I have opened the multimeter and i can see 4 potentiometers : ac, osc, cx, dc, all 200 ohm. Where is the issue ?
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The meter probably rquires calibration. Without the service manual and their recomended calibration reference instruments, it would not be easy to determine and follow through with the recomended procedure. These adjustments generaly interact with other functions. The proper procedure would most likely be able to zero the errors to the design tollerance of the meter.
Many of the low cost meters that I have service had as much as a 1% to
2% error in their readings. The higher end meters were able to be calibrated to better than 0.5% error.I found that on the low cost DVM's, even after a full calibration, there is some offsets in the polarity difference readings, and in the zero offset. The higher cost meters have circuits and calibration procedures for offsets and etc.
I would suggest that if you want a very good volt meter, you should invest in a Fluke, or a Tektroix meter. With these you will not go wrong.
Jerry G. ======
ALPI schrieb:
That's called "rollover error". Have a look at Google:
(rollover error a/d converter)
HTH
Reinhard
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