Author Topic: USA Cal Club: Round 2  (Read 140422 times)

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Offline TiN

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Re: USA Cal Club: Round 2
« Reply #700 on: February 03, 2021, 03:31:40 am »
Some ISPs block FTP port connections, so you can try alternative port 9876 for connections.
YouTube | Metrology IRC Chat room | Let's share T&M documentation? Upload! No upload limits for firmwares, photos, files.
 
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Online Grandchuck

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Re: USA Cal Club: Round 2
« Reply #701 on: February 03, 2021, 01:59:29 pm »
OK, the files have been uploaded using WinSCP (a free download).  Thanks everyone for the help. :-+
 

Offline orin

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Re: USA Cal Club: Round 2
« Reply #702 on: February 03, 2021, 05:32:46 pm »
OK, the files have been uploaded using WinSCP (a free download).  Thanks everyone for the help. :-+

Ah, WinSCP.  I use it all the time at work to get logs from servers I maintain.  Just note that the remote file view doesn't automatically update as files are added/updated, so use the refresh button often.
 
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Offline hwj-d

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Re: USA Cal Club: Round 2
« Reply #703 on: February 12, 2021, 06:53:46 am »
Thanks,
so the PX is also very good!

As in july 2018:

https://www.eevblog.com/forum/metrology/usa-cal-club-round-2/msg1643525/#msg1643525

the PX today is bang on!

(and my dmm6500 too  :-DMM

 :-+

 

Offline JBeale

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Re: USA Cal Club: Round 2
« Reply #704 on: February 24, 2021, 05:17:19 am »
Just curious; any recent news on this topic? I've lost track of where I was on the list.
 

Offline vindoline

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Re: USA Cal Club: Round 2
« Reply #705 on: February 24, 2021, 10:48:01 pm »
Just curious; any recent news on this topic? I've lost track of where I was on the list.

PM sent.

The club is alive and active! Currently KK6IL has the kit. You're next!
 

Offline JBeale

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Re: USA Cal Club: Round 2
« Reply #706 on: March 18, 2021, 01:13:53 am »
A box-full of calibration has landed at my doorstep. With my 6.5 digit Keithley 196 DMM, I am feeling unworthy! So it won't stay here too long.  So far, I have only hooked up the little Arduino Temp-Humidity monitor, and had a quick look at the resistance standards. So far, so good. Apparently I have not been paying attention, because there are more widgets in here than I anticipated.
Code: [Select]
temp_c,humidity,crc16
18.996,55.012,b216
18.991,54.854,dafc
18.988,54.687,35e8
18.981,54.532,b9ee
18.988,54.382,8ebd
18.988,54.208,916e
18.979,54.050,5e74
18.981,53.892,73a0
18.982,53.746,a13c
18.979,53.605,2450
18.978,53.492,c79c
18.964,53.381,bbca
 
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Offline bitseeker

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Re: USA Cal Club: Round 2
« Reply #707 on: March 18, 2021, 02:00:02 am »
It's quite the cornucopia of calibration contraptions. And you've got fresh calibration data from TiN. :-+
TEA is the way. | TEA Time channel
 

Offline rhb

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Re: USA Cal Club: Round 2
« Reply #708 on: March 22, 2021, 11:09:46 pm »
A box-full of calibration has landed at my doorstep. With my 6.5 digit Keithley 196 DMM, I am feeling unworthy! So it won't stay here too long.  So far, I have only hooked up the little Arduino Temp-Humidity monitor, and had a quick look at the resistance standards. So far, so good. Apparently I have not been paying attention, because there are more widgets in here than I anticipated.
Code: [Select]
temp_c,humidity,crc16
18.996,55.012,b216
18.991,54.854,dafc
18.988,54.687,35e8
18.981,54.532,b9ee
18.988,54.382,8ebd
18.988,54.208,916e
18.979,54.050,5e74
18.981,53.892,73a0
18.982,53.746,a13c
18.979,53.605,2450
18.978,53.492,c79c
18.964,53.381,bbca

You, unworthy?    Modest I'd accept, but "unworthy" would be grounds for a cage fight conflict.  That said, it's pretty intimidating when you open the box.

I'm hoping I'll be able to  participate with proper HVAC control in the next round, but it's been going far too slowly to suit me.

I wandered away from cyberspace for quite a while, so I have a lot of catch up to do.

Have Fun!
Reg
 
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Offline Conrad Hoffman

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Re: USA Cal Club: Round 2
« Reply #709 on: March 23, 2021, 04:57:05 pm »
Yeah, I heat with wood and cool with... nothing, so the only good times of the year for me are spring and fall. I can keep the lab at a very consistent 20C for a few weeks. The lab dehumidifier died, so I need to buy a new one.
 

Offline SilverSolder

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Re: USA Cal Club: Round 2
« Reply #710 on: March 23, 2021, 05:52:20 pm »
Yeah, I heat with wood and cool with... nothing, so the only good times of the year for me are spring and fall. I can keep the lab at a very consistent 20C for a few weeks. The lab dehumidifier died, so I need to buy a new one.

Sounds like New England.  There are several hundred milliseconds a year where the temperature is 'just right'!  :D

 

Offline JBeale

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Re: USA Cal Club: Round 2
« Reply #711 on: March 23, 2021, 06:13:04 pm »
Here's a ~ 4 day measurement on my DMM-196, looking at the PX-REF#1 powered by a random 12V wall-wart. I realize that's sort of casual, so I just switched it to +12.00 V from a Power Designs 2005A which is a little bit more stable as a supply.

So far, my DMM-196 (last cal on 6-16-2008) reads 7.04545 V, sigma = 20.5 uV, on 35k samples.
PX-REF#1 box label reads 7.0456 V

According to the provided Arduino/SHT21 sensor, the temperature in the room is 17.5 C +/- 1 C and the relative humidity RH is  57 % +/- 2 % over the time period shown.

The temp/RH sensor reports readings at about 1.5 second intervals. To make it easier to line up the measurements I standardized on reading at the top of every 10 second interval (or the closest reading just after that point). 
Here is a python program that does this with the provided Arduino board T/RH sensor:
https://github.com/jbeale1/DataAcq/blob/master/SerialLog-Even10s.py
« Last Edit: March 23, 2021, 06:30:59 pm by JBeale »
 
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Offline bitseeker

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Re: USA Cal Club: Round 2
« Reply #712 on: April 16, 2021, 06:14:36 am »
Very nice. Great to see another 196 in action. :-+
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Offline maxwell3e10

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Re: USA Cal Club: Round 2
« Reply #713 on: April 19, 2021, 12:02:32 am »
I first found EEVblog forum when I was trying to fix a Keithley 2001 DMM. And now, 600 posts later, this is the meter collection:
Most of these meters have never been adjusted after manufacturing. The only one with current calibration is DMM6500. To calculate the deviations  I used resistor values as reported by Arthur Dent and verified by CalMachine and voltage reported by TiN and also confirmed by CalMachine. Then I used 10 kOhm resistor (9.99979 kOhm) and 10V FX reference (9.999966V) to calibrate my HP3458. In general, it seems all meters drift by comparable amounts.

Another interesting aspect is how much does the calibration change after AutoCal on recent DMMs
.
In particular on 34465 and 34470 meters, it can change a lot. Well, the last time the AutoCal was run on those meters was 2 years ago.  Still ~100 ppm is a big change considering that the temperature has not changed by much and the meters have already been somewhat aged. So, it seems Keysight uses some low-quality components and relying on AutoCal to cancel the drift. This may explain funny drift of 34470 after Autocal. It seems they should force the user to run AutoCal at regular intervals, otherwise the meter can drift a lot.

I also looked at the voltage stability of the FX reference measured by several meters.
Here we see the famous noise bump of Keithley DMM7510 that is prominent not only at 0V but also at 10V.

I also looked at the noise spectral density of the voltage references. For PX reference I compared it with an HP LTZ1000 voltage reference board 03458-66509 that I had. The difference between their voltages was a little more than 100 mV, but I could monitor it using HP3457 on 300 mV range. Another way to measure the noise spectrum is with a very low cut-off (0.03 Hz) high pass filter (100 kOhm and 50 uF) and a low noise amplifier (LNA10 from Alpha lab).  The two measurements agree well  and confirm the noise density of <200 nV/Hz^{1/2} at 0.1 Hz. It should be noted that I divided HP3457 spectrum by a factor of 2, one factor of sqrt(2) comes from taking difference of two LTZ references and another factor of sqrt(2) comes from the fact that DMM with autozero only measures the signal approximately 50% of the time.

I also looked at the noise spectrum of FX reference and found that it is a little higher than one might expect naively from voltage scaling and also has a pronounced oscillation at around 3 kHz. One can see it in the time domain  on the oscilloscope with an amplitude of about 20 uV using a gain 1000 of LNA10 with 100 kHz bandwidth.
Probably putting a capacitor somewhere in the op-amp circuit will get rid of the oscillations.

So this is my report, I am ready to send on the kit unless someone comes up with a quick test idea. It has been very helpful to get access to this calibration gear, thank you everyone for contributing to it and organizing the exchange.

« Last Edit: October 13, 2022, 02:00:34 pm by maxwell3e10 »
 
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Online Andreas

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Re: USA Cal Club: Round 2
« Reply #714 on: April 19, 2021, 05:06:53 am »

I also looked at the noise spectrum of FX reference and found that it is a little higher than one might expect naively from voltage scaling and also has a pronounced oscillation at around 3 kHz.
Probably putting a capacitor somewhere in the op-amp circuit will get rid of the oscillations.

So this is my report, I am ready to send on the kit unless someone comes up with a quick test idea.
Mhm,

did you check the 3 kHz oscillation also for the positive and the 0V output independantly?
The capacitors are already there. (C39 + C40)
https://xdevs.com/article/792x/

I guess that C40 together with R32+R33 is somewhat low against the product (time constant) of R31+C48.
Whereas C39 together with R1-R3 should be about right. (ok somewhat at the limit).

So it should be the 0V output which is more likely to oscillate.

with best regards

Andreas
 
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Offline HighVoltage

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Re: USA Cal Club: Round 2
« Reply #715 on: April 19, 2021, 07:52:45 am »

In particular on 34465 and 34470 meters, it can change a lot. Well, the last time the AutoCal was run on those meters was 2 years ago.  Still ~100 ppm is a big change considering that the temperature has not changed by much and the meters have already been somewhat aged. So, it seems Keysight uses some low-quality components and relying on AutoCal to cancel the drift. This may explain funny drift of 34470 after Autocal. It seems they should force the user to run AutoCal at regular intervals, otherwise the meter can drift a lot.

Nice to have another confirmation on this.

In my experience it is only the 34470A that drifts and NOT the 34465A.
I had two of each and the two 34465A were always spot on after an ACAL, exactly as expected by the book.

The two 34470A started drifting after a few months and it only got worse over time, even if you would use ACAL every day. I still have one 34470A but sold the second one, because it drifted far too much.
I started a thread somewhere here on the forum.
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Offline guenthert

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Re: USA Cal Club: Round 2
« Reply #716 on: April 19, 2021, 03:25:11 pm »
I first found EEVblog forum when I was trying to fix a Keithley 2001 DMM. And now, 600 posts later, this is the meter collection:
Most of these meters have never been adjusted after manufacturing. The only one with current calibration is DMM6500. To calculate the deviations  I used resistor values as reported by Arthur Dent and verified by CalMachine and voltage reported by TiN and also confirmed by CalMachine. Then I used 10 kOhm resistor (9.99979 kOhm) and 10V FX reference (9.999966V) to calibrate my HP3458. In general, it seems all meters drift by comparable amounts.
    Thanks for sharing.  In general (above only prompted to write) I'd like to see error bars on measurements, i.e. estimates of the consistency of the readings.  One way to do that to measure a given artifact with a giving meter multiple times (also reversing polarity to minimize effects of thermal EMF at the artifact<->probe junction) and report the standard deviation.

    We can look up the specifications of those meters to get a hint of how close those measurements could be, but without results from procedures like the one described above, we have no way of knowing how well those specific meters actually performed then.
« Last Edit: April 19, 2021, 03:28:09 pm by guenthert »
 

Online Kleinstein

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Re: USA Cal Club: Round 2
« Reply #717 on: April 19, 2021, 03:46:43 pm »

The two measurements agree well  and confirm the noise density of <200 nV/Hz^{1/2} at 0.1 Hz. It should be noted that I divided HP3457 spectrum by a factor of 2, one factor of sqrt(2) comes from taking difference of two LTZ references and another factor of sqrt(2) comes from the fact that DMM with autozero only measures the signal approximately 50% of the time.

I also looked at the noise spectrum of FX reference and found that it is a little higher than one might expect naively from voltage scaling and also has a pronounced oscillation at around 3 kHz.

The extra factor sqrt(2) for the DMM only sampling the input half the time only applies to white noise, but not the higher 1/f noise part. So the comparison is not that easy.


The broad peak at around 3 kHz does not look like oscillation - it is much to wide for this. It may be just noise amplification from not so ideal compensation, close to instability, but still well on the stable side. The amplitude is also quite small. The frequency is a bit low to be a chopper amplifier residual.
 

Offline maxwell3e10

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Re: USA Cal Club: Round 2
« Reply #718 on: April 19, 2021, 04:32:40 pm »
The two 34470A started drifting after a few months and it only got worse over time, even if you would use ACAL every day. I still have one 34470A but sold the second one, because it drifted far too much.
I started a thread somewhere here on the forum.
I am wondering if doing ACAL frequently is what is contributing to long-term drift. After ACAL there is clearly additional drift, likely from some change in heating of internal components. It maybe that during ACAL some resistor is assumed to be the same for several measurements, but in fact drifts a little and always in the same direction, accumulating the errors.
 

Offline maxwell3e10

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Re: USA Cal Club: Round 2
« Reply #719 on: April 19, 2021, 04:38:27 pm »
The extra factor sqrt(2) for the DMM only sampling the input half the time only applies to white noise, but not the higher 1/f noise part. So the comparison is not that easy.
Yes, good point, I will have to think more about how to do it properly.
The broad peak at around 3 kHz does not look like oscillation - it is much to wide for this. It may be just noise amplification from not so ideal compensation, close to instability, but still well on the stable side. The amplitude is also quite small. The frequency is a bit low to be a chopper amplifier residual.
Yes, its just noise gain peaking, slightly larger compensation capacitor should be able to kill it.
 

Offline maxwell3e10

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Re: USA Cal Club: Round 2
« Reply #720 on: April 21, 2021, 04:09:30 pm »
The kit is on the way back to vindoline, but here is a comparison of voltage drift from several LTZ references (of course measured with another LTZ reference inside the HP3458).
 
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Offline Echo88

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Re: USA Cal Club: Round 2
« Reply #721 on: April 21, 2021, 05:35:01 pm »
Can we get a teardown of the SRS DC205 pretty please?
 

Offline maxwell3e10

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Re: USA Cal Club: Round 2
« Reply #722 on: April 21, 2021, 06:27:21 pm »
Can we get a teardown of the SRS DC205 pretty please?
Yea, I was going to do a teardown, dig into the circuit and see if it can even be improved, but there is a long list of other projects ahead of it now. Here is the picture of the circuit. The op-amps that have guarded traces going to them are OPA192.
 

Offline SirAlucard

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Re: USA Cal Club: Round 2
« Reply #723 on: June 05, 2021, 04:23:22 am »
I'm kind of looking forward to round3, As I kind of used round2 as a calibration round to self calibrate my 3478A, I'd be curious as to see if there was any drift with my DMM since last I had the unit. Verifying if my ebay purchase was indeed a success or not.
 
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Online Grandchuck

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Re: USA Cal Club: Round 2
« Reply #724 on: June 07, 2021, 07:15:51 pm »
Hoping that there will be a 3rd round. 

Your post gave me an idea.  Perhaps there could also be another type of club ... one with a quick turn-around time for a fast check on our instruments.  It could contain two standards: an FX voltage reference and a 10 k resistor.
 
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