Author Topic: USA calibration club  (Read 140217 times)

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Offline Muxr

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Re: USA calibration club
« Reply #125 on: June 21, 2017, 12:08:52 pm »
I wouldn't quite call it useless, but it's pretty flaky. I've hacked around most of the issues and I am actually getting good captures with it on my 3458A. The driver definitely needs attention but in the absence of that these are my workarounds:

- First of all, for some reason I can't have the polling of the instrument in a python loop. I tried multiple things, like destroying objects on each iteration etc.. when you keep polling in a loop there is some residual state or a memory leak caused by the driver which causes the USB subsystem to become locked out. You basically get a USB device driver busy after a while and you are no longer able to poll. The workaround for this is to execute a system process each time you poll.. ugly and annoying but this resolved the issue, I haven't had USB device busy since I did that.
Code: [Select]
        process = os.popen('/usr/bin/python ad_hoc_hp3458a.py')
        list_returned = process.read().split('\n')
        process.close()

        return float(list_returned[-2])
That basically executes the following script and converts the second to last line into float.

Code: [Select]
from ugsimple.GPIB import UGSimpleGPIB
import time
import sys


class Delay(object):
    """ introduces a delay into a while loop
        with a timeout
    """
    def __init__(self):
        self.i = 0
        self.timeout = 50

    def delay(self):
        self.i += 1
        if self.i == 1:
            # no delay on the first run
            return self.i
        time.sleep(0.1)
        if self.i > self.timeout:
            sys.exit(1)
        return self.i


if __name__ == '__main__':
    # Initialize the UGSimpleGPIB USB adapter
    # Requires root permissions (or add the udev rule)
    mygpib = UGSimpleGPIB(debug_mode=False)

    # List Connected Devices
    print mygpib.query_devices()

    # GPIB address of the device
    addy = 22

    data = ''
    d = Delay()
    # sending the command to 3458A
    mygpib.write(addy, "TARM AUTO")

    # reading from device
    while data == '':
        print d.delay()
        data = mygpib.read(addy)

    print 'data: {}'.format(data)

    print ('%.08f' % float(data))

The notable change from the example script the python driver ships with is that I discovered that their read() function is non blocking. Which means if the instrument doesn't respond in time the result just gets abandoned. This caused a lot of missed readings in the past, and since I implemented this hack.. I have not missed a single reading.

I do still get occasional syntax errors, but the polling never gets interrupted, and the readings aren't corrupted by it. It is definitely flakey, and your mileage may vary with other instruments I haven't yet tested it with. But it is a workable solution. I am getting useful captures from it.

For instance see an attached 20hour run:
 

Offline vindoline

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Re: USA calibration club
« Reply #126 on: June 21, 2017, 06:27:24 pm »
I got back into town yesterday to find this waiting for me  :-+ :



The Keithley 196 has been powered up for over a week now, so it should be as stable as it will get. I've powered up the reference at 15.00 V with the Power Designs 4010 and let it settle for 24 hours.




 All my data will have to be taken manually, as my GPIB solution is a work in progress... I will report back soon with some measurements, graphs, etc. and send it on it's way to the next club member!
« Last Edit: June 21, 2017, 06:29:26 pm by vindoline »
 
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Offline bitseeker

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Re: USA calibration club
« Reply #127 on: June 21, 2017, 06:35:14 pm »
That's certainly a nice thing to find when getting home. ;D Looking forward to seeing how everything works out.
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Offline vindoline

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Re: USA calibration club
« Reply #128 on: June 21, 2017, 09:25:45 pm »
I just had a quick look at this project. Looks great! If you get this working, I'll definitely make a batch! Please keep us updated.

vindoline, the boards are in!  Now time to get serious about that firmware...

(I'd be happy to mail you a board for free -- I ordered like 10 of them through dirtypcb's).

Hi CellularMitosis, I've built up the board you were so kind to send. Is this board designed to be able to be programmed via the USB? I have an Arduino I can use as well. I'd like to be able to confirm that I built it up OK. That FTDI chip was the smallest thing I've ever soldered!

No rush, but have you made any progress getting your K196 talking via GPIB yet?

Thanks again!
 
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Offline bitseeker

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Re: USA calibration club
« Reply #129 on: June 22, 2017, 12:40:18 am »
Nice job for a first-timer soldering that tiny pin pitch. :clap:
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Offline cellularmitosisTopic starter

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Re: USA calibration club
« Reply #130 on: June 22, 2017, 02:45:33 am »
Glad the reference arrived!  Nice collection of gear by the way :)

Sadly, I have had to behave like an adult quite a lot recently, and have not made much progress on the firmware.  However, if you have a linux box handy, you can simply plug the USB cable in and run 'dmesg' from the command line, and you should see a message about a new FTDI device being recognized.  If that works, the only untested part would be the ATmega chip, but because it is wired straight up to both the centronics connector and the FTDI chip, there's very little chance that it isn't connected.

I completely forgot to put an ICSP header on the board -- you'll have to remove the chip anytime you want to reprogram it (sorry!).
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Offline alm

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Re: USA calibration club
« Reply #131 on: June 22, 2017, 07:17:50 am »
Or remove it only once to program a bootloader in it.
 
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Offline vindoline

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Re: USA calibration club
« Reply #132 on: June 22, 2017, 12:37:03 pm »
Glad the reference arrived!  Nice collection of gear by the way :)

Sadly, I have had to behave like an adult quite a lot recently, and have not made much progress on the firmware.  However, if you have a linux box handy, you can simply plug the USB cable in and run 'dmesg' from the command line, and you should see a message about a new FTDI device being recognized.  If that works, the only untested part would be the ATmega chip, but because it is wired straight up to both the centronics connector and the FTDI chip, there's very little chance that it isn't connected.

I completely forgot to put an ICSP header on the board -- you'll have to remove the chip anytime you want to reprogram it (sorry!).

Thanks. I plugged the adapter into my Mac OS X machine and the USB adapter info showed up in the console. So it looks like a success! Like a lot of us, the gear is mostly from eBay cheap and repaired/refurbished by me.
 

Offline vindoline

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Re: USA calibration club
« Reply #133 on: June 22, 2017, 12:39:05 pm »
Or remove it only once to program a bootloader in it.
I'll give that a try!
 

Offline vindoline

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Re: USA calibration club
« Reply #134 on: June 23, 2017, 07:31:10 pm »
OK, the SVR-T is on its way to Conrad! I'll post my measurement results as soon as I have a chance to do some analysis - hopefully this weekend. Thanks for the fun!
 

Offline Conrad Hoffman

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Re: USA calibration club
« Reply #135 on: June 23, 2017, 10:06:50 pm »
Posting a lookout and warming up the meter!
 

Offline CatalinaWOW

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Re: USA calibration club
« Reply #136 on: June 24, 2017, 03:35:43 pm »
Getting my act together for the arrival in Oregon I finally got GPIB logging working.  After a few weeks of frustration fighting the LQ Electronics USB battle I bought a National Instruments one (under $200 on Ebay) and other than the requirement for multiple reboots during installation of the various NI drivers it has been a dream.  A few minutes with EZ-GPIB and I was logging 3 voltmeters.

The attached shows about 12 hours watching a AD581 with a 1996 date code with one HP3457A and two HP3478As.  Still need to rig up temperature logging as the voltage shows the long overnight drift down in temperature followed by a sudden drop as I opened the windows to the lab to let the cool morning air in.  Once that is in place will decide if I need to do more for temperature compensation.
 
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Offline Conrad Hoffman

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Re: USA calibration club
« Reply #137 on: June 24, 2017, 06:41:32 pm »
If the tools haven't been mentioned before, I found http://www.ke5fx.com/gpib/readme.htm to be very useful in my GPIB programming.
 
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Offline bitseeker

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Re: USA calibration club
« Reply #138 on: June 24, 2017, 08:47:06 pm »
I didn't know Prologix.exe in the GPIB Toolkit can work with "an otherwise-unsupported TCP/IP or serial adapter." I'll have to check that out.
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Offline CatalinaWOW

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Re: USA calibration club
« Reply #139 on: June 25, 2017, 01:25:12 am »
Had non hobby related commitments today.  Some conclusions from looking at this first run.

1.  There isn't enough noise on this source to allow extending the resolution of the HP3478s by averaging measurements. 

2.  There is enough to extend the 7.5 digits from the HP3457.  Still have some work to do to see if the stability is good enough for this to translate into precision, but so far it seems promising.

Plenty of interesting things to do.  Hope I get time.
 

Offline Conrad Hoffman

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Re: USA calibration club
« Reply #140 on: June 26, 2017, 11:24:48 pm »
A small and mysterious box was on the dinner table when I arrived home tonight. More reports to follow!  :-DMM
 
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Offline bitseeker

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Re: USA calibration club
« Reply #141 on: June 26, 2017, 11:48:15 pm »
Ooh, intriguing. Looking forward to the forthcoming reports. :-+
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Offline Conrad Hoffman

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Re: USA calibration club
« Reply #142 on: June 27, 2017, 12:15:57 pm »
A quick measurement shows that even though my last traceable calibration was over 13 years ago, I'm showing the standard within 3 ppm of 10V on the 3455A. The standard seems to warm up within a few minutes, compared to the rest of my equipment that takes a couple hours for good stability. I'm going to use the 845 null meter and compare the standard with my "golden" 731A. It occurs to me that I can put a DVM on the output of the 845 and do some data logging on that. Need to check the long term drift of the 845.

The big problem in my lab is temperature. It's about 20C right now. I heat with wood, and heating season is over, so it's not so easy to warm things up. Need to find a small heater and see if I can stabilize things a bit higher over the next few days. RH is controlled at 60%. Idea- I can lower the RH setting which will also heat up the room.

Do we have an idea of the tempco of the standard? Line regulation? I can check the latter easily enough.
 

Offline Muxr

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Re: USA calibration club
« Reply #143 on: June 27, 2017, 03:06:47 pm »
Unfortunately, I didn't have my temp measurement rig setup when I had it. So can't really speak on the Tempco.

SVR-T has the NTC based temperature compensation in its trim circuit, and I did notice much less temperature related drift with the jumper on.

SVR (non T version) without NTC is rated at 5 ppm / ÂșC.

http://www.gellerlabs.com/svr%20series.htm

edit: post where I shared my measurements with trim jumper on and off: https://www.eevblog.com/forum/metrology/usa-calibration-club/msg1222185/#msg1222185
« Last Edit: June 27, 2017, 10:43:00 pm by Muxr »
 

Offline vindoline

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Re: USA calibration club
« Reply #144 on: June 27, 2017, 06:21:33 pm »
Hi, I've finally had a chance to look at the SVR-T measurements that I made last week. First off, I'm an organic chemist, not an ee - I still have a lot to learn about this metrology stuff! My good meter is an old Keithley 196 6.5 digit. The only thing I know about its calibration history is that I haven't done it! It is in nice shape and seems very stable to me. The 196 has GPIB, however I don't have an automated measurement system working yet - it's in the planning stage for now.

I powered the SVR-T at 15.00 v from a very stable and quiet Power Designs 4010 precision power source. I let everything stabilize overnight before I took any data. For the cable connection between the SVR-T and the 196 I tried the various solutions "in the box" from cellularmitosis as well as my own teflon insulated twisted pair from plenum grade Cat5e and standard RG-59 coax with Pomona BNC to banana plug adapters. I was unable to discern any difference between any of them. In the end I used the coax cable for the measurements.

What I did was each morning for 3 days I took manual readings of the K196 every 30 seconds for 15 min. I checked the lab temperature on my Fluke thermometer at the beginning and end of each run. For the third run I decided to record the temperature every 30 sec also.

Looking at the 3rd day plot with the temperature, it appears that the slight voltage drift may be correlated with the temperature fluctuation. Like Conrad, my lab is in my basement. Its temp and humidity is not well controlled and I took no measures to prevent drafts on the SVR-T. It looks like that might be a good idea.

I also took 10 min of data on day 3 with the Keithley 196 averaging filter ON. It did seem to smooth out the data somewhat, but not entirely. I'm still working on understanding how this filter works, so I didn't use it for the main part of the experiment.

Overall, the SVR-T appears to be very stable and quiet. In the time I had it up and running it's value changed less than 10 PPM.

Graphs of the data are below for your enjoyment.
 
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Offline vindoline

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Re: USA calibration club
« Reply #145 on: June 27, 2017, 06:36:33 pm »
Hi, one of the other projects/interests I have is noise measurement. A while back I built up the "Curiously Low Noise Amplifier" from Charles Wenzel's website (http://www.techlib.com/electronics/audioamps.html#curiously%20low%20noise). This is a JFET front end low noise preamp with a gain of x100. The output is measured on an HP3400A thermally responding true RMS AC voltmeter using a simple RC filter to give an equivalent noise bandwidth of 500 kHz. The SVR-T measured about 4 mV rms which corresponds to 40 uV noise on the SVR-T output. That sounds pretty good to me!
 
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Offline bitseeker

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Re: USA calibration club
« Reply #146 on: June 27, 2017, 06:48:54 pm »
First off, I'm an organic chemist, not an ee - I still have a lot to learn about this metrology stuff!

No worries. I'm an EE and I enjoyed organic chemistry, too.

Quote
My good meter is an old Keithley 196 6.5 digit. The only thing I know about its calibration history is that I haven't done it! It is in nice shape and seems very stable to me. The 196 has GPIB, however I don't have an automated measurement system working yet - it's in the planning stage for now.

You're in good company. CM and I also have a 196, probably with very similar history (I know I haven't calibrated mine, either). Great job with the manual logging!

Hi, one of the other projects/interests I have is noise measurement. A while back I built up the "Curiously Low Noise Amplifier" from Charles Wenzel's website (http://www.techlib.com/electronics/audioamps.html#curiously%20low%20noise). This is a JFET front end low noise preamp with a gain of x100. The output is measured on an HP3400A thermally responding true RMS AC voltmeter using a simple RC filter to give an equivalent noise bandwidth of 500 kHz. The SVR-T measured about 4 mV rms which corresponds to 40 uV noise on the SVR-T output. That sounds pretty good to me!

That is very cool. Added to my to-do list. ;D
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Offline Conrad Hoffman

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Re: USA calibration club
« Reply #147 on: June 27, 2017, 08:33:00 pm »
Long ago I had (I think) a 195. Same brown case. The voltage regulator ran astoundingly hot. I don't know if the 196 suffers from the same thing, but I added an extra piece of aluminum sheet to get the temp down a bit. Just something to check.

When I get home tonight I'll try some noise measurements.
 

Offline cellularmitosisTopic starter

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Re: USA calibration club
« Reply #148 on: June 27, 2017, 10:31:22 pm »
Indeed, I found a surprise when I stuck a temperature probe into one of the input jacks of my 196 (it read about 106F).

I ran the unit using a Kill-a-watt, and it only draws 14 watts, which seems reasonable.  I suppose a 14-watt light bulb probably would raise the temperature of a sealed plastic case to 106F...

I've been brainstorming about moving the transformer and regulators outside of the case to see if I can get the temp down, or possibly hacking the case and adding a large double-sided heat sink.  My concern is that the banana jacks will see a ~30F gradient, which could be inducing a large EMF (or perhaps only if they aren't both being heated evenly?).

I just scored a 34401a off of ebay so I'm now in the position to see if I can device some experiments to quantify the effect of this somewhat high internal temperature (and I'll have a reference to check the performance of any mods against)
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Offline cellularmitosisTopic starter

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Re: USA calibration club
« Reply #149 on: June 27, 2017, 10:33:20 pm »
btw, great job everyone on the data you're collecting!
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