Author Topic: Prema 5017 / 8017  (Read 12365 times)

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Offline branadic

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Prema 5017 / 8017
« on: October 23, 2017, 05:51:25 pm »
I start a new topic on Prema 5017 / 8017. I here posted the question:

What noise would one expect, if DMM measures its own voltage reference in 10V range?

I'm currently observing the reference voltage on my Prema 5017 by itself and I'm the opinion that the noise is rather high. Attached is a picture directly after powering the unit up with capturing data with 0.5Hz repetition rate. I will go one measuring and will then measure the reference voltage with 3458A for comparison. Maybe there is some room for improvement within the circuit by changing some opamps by lower noise types?



For me ~30µVpp is rather high noise in 10V range, when comparing the result with my own LM399.
I found LM399 connected to the non-inverting input of an AD707, which is an improved pin-for-pin replacement for the LT1001, but obsolete by now. I will go on measuring within the cicuit to find where those excessive noise is coming from and how the schematic looks like.

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Offline Kleinstein

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Re: Prema 5017 / 8017
« Reply #1 on: October 23, 2017, 06:32:48 pm »
The LM399 is way more noisy than a reasonable quality OP. So changing the OP in the reference section has little chance to improve noise. If at all drift might change, if the old one was a poor choice.
The first point would be to find out where the noise is mainly comming from. Usually there are 3 main contributions:
1) input amplifier (including input protection)
2) ADC itself
3) the reference

I would first test the noise with a shorted input. This excludes more of the reference noise. For the 10 V range the input amplifier should not add very much, as the ADC is usually way more noisy than the input amplifier. It is only in the lower ranges that the input amp gets important. Usually the main noise source in the lowest range. The high voltage ranges with a divider might not help very much in the analysis, as they are similar to the lower ones.

Comparing the noise with a short to the noise of a low noise voltage source (e.g. 9 V block) makes the LF reference noise visible.

Normally the noise when measuring the internal reference should be similar to the noise with a short, but it depends - things like filtering could change things for some time scales.
 

Offline The Soulman

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Re: Prema 5017 / 8017
« Reply #2 on: October 23, 2017, 07:03:11 pm »
...
The first point would be to find out where the noise is mainly comming from. Usually there are 3 main contributions:
1) input amplifier (including input protection)
2) ADC itself
3) the reference
...

I'd like to add a 4) measurement setup (includes connections, induced noise, etc.)

When measuring the internal reference: how was the connection made and was the housing closed?
« Last Edit: October 23, 2017, 07:20:49 pm by The Soulman »
 
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Online Andreas

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Online Andreas

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Re: Prema 5017 / 8017
« Reply #4 on: October 23, 2017, 07:18:17 pm »
The LM399 is way more noisy than a reasonable quality OP.

But a good (selected) LM399 has around 4uVpp 0.1 - 10 Hz noise.
Further reduction takes place (~1uV) when integration over 2 seconds is done.

with best regards

Andreas
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #5 on: October 23, 2017, 07:51:30 pm »
The LM399 is way more noisy than a reasonable quality OP. So changing the OP in the reference section has little chance to improve noise. If at all drift might change, if the old one was a poor choice.
The first point would be to find out where the noise is mainly comming from. Usually there are 3 main contributions:
1) input amplifier (including input protection)a
2) ADC itself
3) the reference

I would first test the noise with a shorted input. This excludes more of the reference noise. For the 10 V range the input amplifier should not add very much, as the ADC is usually way more noisy than the input amplifier. It is only in the lower ranges that the input amp gets important. Usually the main noise source in the lowest range. The high voltage ranges with a divider might not help very much in the analysis, as they are similar to the lower ones.

Comparing the noise with a short to the noise of a low noise voltage source (e.g. 9 V block) makes the LF reference noise visible.

Normally the noise when measuring the internal reference should be similar to the noise with a short, but it depends - things like filtering could change things for some time scales.

I'm currently performing the short circuit test. Short circuit measurement indicates noise in the same order as measuring the internal reference itself.

Quote

I'd like to add a 4) measurement setup (includes connections, induced noise, etc.)

When measuring the internal reference: how was the connection made and was the housing closed?

No problem, the measurement was done with the case closed and some probe put through some small opening in the chasis.

Question: What noise would one expect, if DMM measures its own voltage reference in 10V range?

I'm currently observing the reference voltage on my Prema 5017 by itself and I'm the opinion that the noise is rather high.

Hello,

if I look at the datasheet of the ADC the noise is explainable for me:

https://www.ohh.de/5610.htm

2 seconds integration time correspond to N1=30 and N2 = 10 thus around 23.6 bits.
Input range is +/-30 V so 60V / 23.6 bits gives 4.7uV.

If I assume that the 3 sigma has to be multiplied (and not divided)
we get around 15uVp / 30uVpp noise alone from the ADC.

So I fear that the analog path with 2uVpp estimated maximum noise is not the mayor source of the noise.

with best regards

Andreas

Seems to be the most reasonable answer by now. However, PRI 5610 was offered in some 28pin DIP package while the Pr BK7 adc inside the Prema 5017 is in a 20pin DIP package, so I expected some difference between both devices also in performance.



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« Last Edit: October 23, 2017, 09:10:32 pm by branadic »
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Offline Kleinstein

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Re: Prema 5017 / 8017
« Reply #6 on: October 23, 2017, 08:07:06 pm »
The LM399 is way more noisy than a reasonable quality OP.
But a good (selected) LM399 has around 4uVpp 0.1 - 10 Hz noise.
...
For a voltage reference the noise of the LM399 is not that bad, but for comparison the 0.1-10 Hz noise for an OP07 is around 0.4 µV. The 1/f noise cross over for the LM399 is also not that different from precision OPs, so looking at different frequency bands would not change that much on the ratio. The LM399 is more noisy than the OP07  at any reasonable frequency. This probably still works for the 741 and LM358.

It takes a really not suitable CMOS OP like the MCP6002 to get something like 6 µV_pp noise.

Also remember that noise from different sources adds like squares. So it would not be a row of 10  OP07 configured as a buffer to give a 4 µV noise, but 100.

OPs noise can be a problem if at a position where the noise is amplified.

One reason for the rather high noise is the 30 V range used to measure 7 V. This range already uses a divider at the input - a divider by 10 and the 3 V if you are lucky, but it could be even divide by 100 and the  300 mV range.
 

Offline zhtoor

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Re: Prema 5017 / 8017
« Reply #7 on: October 23, 2017, 09:23:21 pm »
power wires going right over the lm399 reference? is that okay. right next to the toroidal filter core?
 

Offline carl_lab

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Re: Prema 5017 / 8017
« Reply #8 on: October 24, 2017, 02:36:11 pm »
power wires going right over the lm399 reference? is that okay. right next to the toroidal filter core?
I think that's the input wires.
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #9 on: October 24, 2017, 04:39:20 pm »
power wires going right over the lm399 reference? is that okay. right next to the toroidal filter core?
I think that's the input wires.

Correct. This is the original wiring, even in my unit.

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Offline branadic

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Re: Prema 5017 / 8017
« Reply #10 on: October 25, 2017, 05:23:20 pm »
So Andreas seems to be absolutly right. I performed a "short" measurement on my DVM with integration time of 2s (values 0 - 4.900), 20s (4.900 - 8.300) and 100s (8.300 - till end) in the last days. At 100s integration time the stability of the measurement is mainly dominated by changes in ambient temperature, while noise is as low as ~1.5µVpp (in +/-30V range).

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Online e61_phil

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Re: Prema 5017 / 8017
« Reply #11 on: October 25, 2017, 06:27:34 pm »
It's a pity that this DMM has such ranges (30V). In this case a 10V to 1V transfer can't benefit from the linearity.
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #12 on: October 25, 2017, 08:57:30 pm »
It's a pity that this DMM has such ranges (30V). In this case a 10V to 1V transfer can't benefit from the linearity.

Don't get this statement as the DVM uses 300mV, 3V, 30V, 300V and 1000V ranges, which is quiet useful when measuring a 10V reference with slightly higher output voltage, while a normal 10V range would already go into overload.

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Online e61_phil

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Re: Prema 5017 / 8017
« Reply #13 on: October 26, 2017, 08:11:45 am »
The HP ones normaly have an overrange to 120%. So if your 10V reference is more than 20% off, than the range shouldn't be your problem.

Another disadavantage of the 30V range is the input impedance. On all DMMs I know with this 3 instead of 1 FS the high impedance input is only available up to 3V. Therefore, you can't measure 10V directly which such a DMM. You will always have at least an attenuator in the input path. Such a design will not help to reduce noise.


It would be very interesting to do a detailed comparison of the 5017 against a 34401A.

Do you have a computer controllable calibrator to measure the linearity of the 5017 against a 3458A?
« Last Edit: October 26, 2017, 08:16:48 am by e61_phil »
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #14 on: October 26, 2017, 03:26:09 pm »
Quote
Do you have a computer controllable calibrator to measure the linearity of the 5017 against a 3458A?

No. :(
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Offline The Soulman

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Re: Prema 5017 / 8017
« Reply #15 on: October 26, 2017, 11:30:23 pm »
Quote
Do you have a computer controllable calibrator to measure the linearity of the 5017 against a 3458A?

No. :(

If you can do simultaneous data-logging on the 5017 and 3458A you don't need a accurate calibrator, only a bunch of (noise free..)
voltage points, measure those at the same time and plot/compare.
Making a graph of both meters while measuring a slowly discharging capacitor could be all you need.
 

Online e61_phil

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Re: Prema 5017 / 8017
« Reply #16 on: October 27, 2017, 05:04:41 am »
A capacitor can't work. I believe for the best result the Prema will need 100s. Therefore, your capacitor should stay sub-ppm stable over 100s. Even if that would be possible, how long should it take from 10V to 0?

Nevertheless, it is of course enough to take any datapoints within in range and measure them with both meters. Measuring simultanously is always a good idea in this case. I also triggeded both instruments simultanously over GPIB. A controllable calibrator is very convienient if you plan to do severeal runs with 100 datapoints.

I also tried to measure linearity with a SR1010. This won't give you 100 datapoints, but no 3458A is needed.
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #17 on: October 27, 2017, 05:31:51 pm »
The maximum I have at hand is a Burster 3401 and a Burster 6401, a 5 decade voltage standard. Nothing for automated measurements though.

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Re: Prema 5017 / 8017
« Reply #18 on: October 27, 2017, 06:02:31 pm »
Is it sub-ppm stable over a few minutes? That should be enough together with a 3458A
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #19 on: January 02, 2018, 06:51:59 pm »
Is it sub-ppm stable over a few minutes? That should be enough together with a 3458A

This question in mind I measured one of the Burster Mikromat DC Standards Typ 3401 we have some 8 hours with our 3458A, both running 24/7 the last weeks, so everything is fully warmed up. Burster DC Standards are based on 1N827.

It seems my LM399 based reference with it's 10V output is even more stable, beside higher noise. Burster 3401 is mains line power, while my reference is powered by a lab power supply. I wonder if this noise can be reduced by using a battery supply? Need to test that.

https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1389741/#msg1389741

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« Last Edit: January 03, 2018, 11:01:53 am by branadic »
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Online e61_phil

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Re: Prema 5017 / 8017
« Reply #20 on: January 02, 2018, 09:31:49 pm »
Hi,

interesting data! Is it possible to plot the temperature against the output voltage? Or do you simply have some raw data for us?

I like the (old) Burster stuff :)
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #21 on: January 02, 2018, 10:46:42 pm »
Sure, attached are the plot and the raw data set.

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Offline branadic

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Re: Prema 5017 / 8017
« Reply #22 on: February 02, 2018, 07:27:34 pm »
I had a call today with Prema respective Mr. Stricker. He remembered that I was once searching for a Prema 5017 / 8017 and wanted to offer me a unit. That said, if you are interested in a Prema device just write to Mr. Stricker and let him know. Most likely you get a mail and the possibility to get what you were searching for with the guarantee of a working unit.

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Offline bozidarms

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Re: Prema 5017 / 8017
« Reply #23 on: February 27, 2018, 05:01:50 pm »
Hi brandic,

many thanks for extremely useful info -
for years, i have been watching for one Prema 8017, no luck at all, seems almost like one unobtainium.
And now, finally one refurbished, fresh calibrated and adjusted unit is on the way to me - great :-+ ;D :-+
« Last Edit: February 28, 2018, 09:57:56 pm by bozidarms »
 

Offline branadic

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Re: Prema 5017 / 8017
« Reply #24 on: September 16, 2018, 09:05:31 pm »
There is currently a Prema 8017 available on the bay. Even though stated as defect there seems to be only an issue while booting. Nothing that sounds unfixable.

-branadic-
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