Possible problem with Prema 6047 or 6048 meters (new EPROM received)

Possible problem with Prema 6047 or 6048 meters (new EPROM received)
Posted by perdrix on 24 Jan, 2018 01:51
Hi all,

I've noticed something about the behaviour of my Prema 6048 that leads me to suspect a firmware problem

I'd like to determine whether this is a problem unique to me or a common one.

If you own either Prema 6047 or 6048, I'd be most grateful if you could undertake the following test sequence with the meter nicely warmed up:
- Power cycle the meter to ensure we are starting with a clean sheet.
- Select the 20V DC range and 4 second integration time
- Connect a stable 10V (or so) source
- Record the meter reading after allowing it to stabilise for a few readings
- Swap the +ve and -ve leads
- Record the meter reading after allowing it to stabilise for a few readings
- Remove the leads and install a shorting link
- Record the meter reading after allowing it to stabilise for a few readings
- Press "Zero" and allow it to complete the null
- Re-connect the 10V source
- Record the meter reading after allowing it to stabilise for a few readings
- Swap the +ve and -ve leads
- Record the meter reading after allowing it to stabilise for a few readings
Please post your readings to the thread.

Thanks
David Partridge

#3 Reply
Posted by hankee on 24 Jan, 2018 20:42
I have seen this effect , although much smaller, with all Prema's I have (had) , a 5000, 2 times 6001 and a 6030.
It looks to me this is something in the Prema design.
The effect was 10 to 20 ppm with my dmm's, this is probably within the specs but this difference between positive and negative voltage measurement it is quite annoying.

#4 Reply
Posted by Kleinstein on 24 Jan, 2018 20:46
Comparing positive and negative reading of the same stable voltage is one way for a spot check on linearity. Depending on the meter and speed of the readings there can be settling effects too. Of cause the measurement only makes sense with the zero offset well set.

#5 Reply
Posted by Mickle T. on 24 Jan, 2018 20:51
This is the Prema's design flaw due to unipolar ADC and Inp-Amp output polarity switching. AFAIR it described in the Service Manual.

#6 Reply
Posted by perdrix on 24 Jan, 2018 21:19
The issue is to do with HOW the meter handles the zero offset when you use the Zero command. Please if you do have one of these meters, I'd appreciate you doing the test. If (as I suspect) there is a firmware problem, I'd like to persuade Pream to issue updated EPROM images. I do however need the data to determine if this is just a problem with this meter or a general one.

Dave

#8 Reply
Posted by perdrix on 25 Jan, 2018 18:11
It would appear that Prema will send me (for a small fee) a replacement EPROM with the latest firmware, but without the factory calibration constants specific to my meter.

I've asked If I can post the ROM contents ...

Dave

#12 Reply
Posted by perdrix on 31 Jan, 2018 03:48
I'm ahead of you

I already determined where the factory calibration data is stored in the EPROM, so just a bit of work with a hex editor (with luck and a following wind) ...

Dave