cie 7905a multimeter offset

[ALPI]

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 ?

 

[Jerry G.]

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.
======

 

[Jamie]

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 ?

I have a fluke bench meter at work that will give you a different
reading of the average if you flip the leads around.
This normally happens if the signal is not steady.

Meter design will average an signal depending on it's
duty cycle. if you had a perfect 50% duty cycle DC pulse
train, then you would get the same reading either way and
it would be 50% of the actual Peak .

 

[Lynn]

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 ?

IT'S ON GOOGLE. GOOGLE IS YOUR MOTHERFUCKING FRIEND, MOTHERFUCKER.

 

[Reinhard Zwirner]

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 ?

That's called "rollover error". Have a look at Google:

(rollover error a/d converter)

HTH

Reinhard