Author Topic: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)  (Read 59673 times)

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Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #250 on: February 11, 2021, 04:51:02 am »
I have two very old National Instruments Ethernet GPIB controllers (both damaged during that same storm that I believe took our my PROM programmer).   These are no longer supported by NI and I had to reverse engineer the protocol then write my own software to control them.   

I tried a few more tests with the high speed but no luck.  It's always coming up with the same error.

This is looking at the newer code that I described.  In the saturation picture, the blue is looking at the time from reading to reading.  ASRate is the average.   The wide swing is due to how I buffer the streamed data.   The white is the input signal.   Driving the meter deep into saturation. 

The second plot is looking at the in-range signal.

I wonder if there was just too much overhead sending data to the serial port.  Maybe the GPIB and parallel ports were more efficient for coding the firmware.    Oh well.   

Offline garrettm

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #251 on: February 11, 2021, 04:54:04 am »

What exactly is your GPIB adapter, @garretm?

I have a National Instruments GPIB-232CT-A here, which I actually quite like - but I have never attempted anything particularly high speed with it.

I'm using an IOGear Serial488A Bus Converter I picked up for $15. It works much better with modern IEEE488.2 GPIB instruments that use standard GPIB terminations (EOS and EOI) rather than custom ASCII termination characters that the 8505/6A was designed to use (presumably for speeding up transactions). The 8500 series' custom termination characters are what break functionality with basic GPIB controllers as I've discussed previously. These older instruments require a full function GPIB controller to properly control HS data flow.

Here's an interesting read regarding GPIB termination characters and binary data for newer instruments.

https://forums.ni.com/t5/Instrument-Control-GPIB-Serial/Default-GPIB-termination-character/td-p/242545?profile.language=en

And here's a programming tutorial for SCPI based GPIB instruments.

https://web.archive.org/web/20070320000922/https://www.few.vu.nl/~elec/products/download/GpibProgTut.pdf
« Last Edit: February 11, 2021, 07:00:18 am by garrettm »
 
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Offline garrettm

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #252 on: February 11, 2021, 06:20:40 am »
I have two very old National Instruments Ethernet GPIB controllers (both damaged during that same storm that I believe took our my PROM programmer).   These are no longer supported by NI and I had to reverse engineer the protocol then write my own software to control them.   

I tried a few more tests with the high speed but no luck.  It's always coming up with the same error.

This is looking at the newer code that I described.  In the saturation picture, the blue is looking at the time from reading to reading.  ASRate is the average.   The wide swing is due to how I buffer the streamed data.   The white is the input signal.   Driving the meter deep into saturation. 

The second plot is looking at the in-range signal.

I wonder if there was just too much overhead sending data to the serial port.  Maybe the GPIB and parallel ports were more efficient for coding the firmware.    Oh well.   

I'm sad to hear the ! toggle / ext. trigger hacks didn't pan out. It would have been nice to one-up Fluke and have HS readings with the serial interface.

I have a spare GPIB controller if you want it. The lid needs some tape to stay closed, but it works. I'd let it go for 8 bucks + shipping. FedEx Smart Post might be the cheapest method, but maybe one of the Post Office Priority options could be cheaper. But for idle curiosity, maybe it’s not worth it?

Did you write the software you've been showing screen shots of? I quite like it. It’s interesting to see the large spikes in latency from buffering. What is the frequency of the sinusoidal input signal? Digitizer operation looks promising if one can get the HS sampling mode to work.

How are you decoding the 5 to 6 byte binary data (for 5.5/6.5 and 7.5 digit readings, respectively). Looks like it might be a little more complicated to convert to a double. I'll give it a go tomorrow and upload a snippet if anyone is interested.
« Last Edit: February 11, 2021, 06:30:27 am by garrettm »
 

Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #253 on: February 11, 2021, 01:41:37 pm »
I'm sad to hear the ! toggle / ext. trigger hacks didn't pan out. It would have been nice to one-up Fluke and have HS readings with the serial interface.

I have a spare GPIB controller if you want it. The lid needs some tape to stay closed, but it works. I'd let it go for 8 bucks + shipping. FedEx Smart Post might be the cheapest method, but maybe one of the Post Office Priority options could be cheaper. But for idle curiosity, maybe it’s not worth it?

Did you write the software you've been showing screen shots of? I quite like it. It’s interesting to see the large spikes in latency from buffering. What is the frequency of the sinusoidal input signal? Digitizer operation looks promising if one can get the HS sampling mode to work.

How are you decoding the 5 to 6 byte binary data (for 5.5/6.5 and 7.5 digit readings, respectively). Looks like it might be a little more complicated to convert to a double. I'll give it a go tomorrow and upload a snippet if anyone is interested.

Thank you very much for the offer.   I'm just using the meter as a source of entertainment and don't really have a need for it.  Saving it from the dumpster but most likely it will become a dust collector.  It's a bit of history with it's thermal technique and high resolution.   

Yes, I wrote that software.  I use LabView, which is now free for home use.  It's a very good engineering tool.   I adopted it back in the 90s as it makes writing software like this a simple task and has saved me a lot of time over the years.   
 
I believe the 5-byte is pretty much the same as the 3-byte.  Maybe there's a IEEE standard for these two formats.   2's comp is done already, I'm guessing to help speed things up and the exponent isn't fixed like the 3-byte, so you will need to multiply by 10^X.  There's no error checking built into the 5-byte.  In my case, I limit the range to +/- 10e12 for any reading sent from the meter.   If you see a reading like 0.45423E225, it may not be a correct answer and is out of sync with the data stream.  :-DD

Looking at the plot I posted, we can see the sample rate is 25ms and there are 3100 samples.  0.025 * 3100 = 78 seconds.    There are about 7.5  cycles,  so 78 / 7.5 is about 10 seconds per cycle or 1 / 10 = 0.1Hz.     

Sampling at 40Hz, it's pretty limited.  I think that's on par with my UNI-T UT181A after I made use of the bar graph data.   In the other graph, I had started out at 7ish Hz and then slowed it down. 

Offline dietert1

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #254 on: February 11, 2021, 04:55:55 pm »
I also gave up on the '!' for the time being, since it did not run reliably. After two hours or so (with roughly a million of readings) i would find 0D and 0A in the binary data where it doesn't belong. It seems correlated with blocking operations on the Windows host. Seems like the instruments go to another mode on output overrun. While waiting for the AB-25 to arrive, i am using our two Flukes with "S2", at about 10 readouts per second and calculating averages every 320 samples. There is enough noise in those data to get reasonable averages. So this gives me two 8 digit DVMs. Sounds strange?

These instruments can be used for serious work. There is some learning though. Since i am trying to characterize a low noise reference at levels of 1 uV and below, it's important to run the instruments at the proper operating temperature. The internal references are tuned for running the instrument at 23 °C ambient, whatever that means. I mean if you stack instruments, each one will have a different temperature. And our Lab has 19 to 20 °C during working hours and 17 °C during the night. Currently i am trying to cover the instruments to protect them from air drafts and at the same time rise their operation temperature to a better working point. Meanwhile i found a setup where one instrument exhibits a positive and the other one a negative TC  - of similar magnitudes, so the averages are good for 0.1 uV during working hours. But it's still experimental. If i want to use it in summer, we need a cabinet with temperature control.

Regards, Dieter
« Last Edit: February 11, 2021, 04:57:42 pm by dietert1 »
 

Offline m k

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #255 on: February 11, 2021, 05:07:49 pm »
With unlimited binary data there are no other way than external end or time out.

If data is #13#13 the thing is clear and no extras are needed.
On the other hand if data is #0#0#0 there is no way to know when it ends without something external.

Trigger from NI-488.2M manual

Code: [Select]
Send(0, fluke, "VAC; AUTO; TRIGGER 2; *SRE 16", 29L, NLend);
sum = 0.0;
for (m=0; m < 10 ; m++) {
  Send(0, fluke, "*TRG; VAL1?", 11L, NLend); // Trigger the Fluke
  WaitSRQ(0, &SRQasserted);                  // Wait for the Fluke to assert SRQ
  ReadStatusByte(0, fluke, &statusByte);     // Be sure that the MAV is set
  Receive(0, fluke, buffer, 10L, STOPend);   // Read the measurement
  buffer[ibcnt] = '\0';
  printf("Reading : %s\n", buffer);
  sum = sum + atof(buffer);
}
Code: [Select]
ibwrt (dmm, "F1R0S2T4", 8);
for (sum=0, x=0; x <= 10; x++) {
  ibtrg (dmm);
  ibrd (dmm, rd, 13);
  sum = sum + atof(rd);
}

STOPend(int) is defined as EOI or EOS, 0x0 - 0xff there will terminate there.

Second code is getting 13 bytes.
Advance-Aneng-Appa-AVO-Beckman-Danbridge-Data Tech-Fluke-General Radio-H. W. Sullivan-Heathkit-HP-Kaise-Kyoritsu-Leeds & Northrup-Mastech-OR-X-REO-Simpson-Sinclair-Tektronix-Tokyo Rikosha-Topward-Triplett-Tritron-YFE
(plus lesser brands from the work shop of the world)
 

Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #256 on: February 11, 2021, 08:20:55 pm »
...
After two hours or so (with roughly a million of readings) i would find 0D and 0A in the binary data where it doesn't belong.
...
Regards, Dieter

Even with the serial port, I see it do some pretty strange things.   Some times it starts out slow then speeds up.  I've had the meter get to a point where I could not do anything but power cycle it to shake it loose.   But, I am playing with some odd conditions and their software group may not have considered them.   Under normal use, it seems to be fairly reliable.   

You ordered the application note.  Nice.  I haven't had time to hunt for it.   

Quote
With unlimited binary data there are no other way than external end or time out.
Sure you can.  Knowing something about the data is the key and in this case, the data is very slow so there is plenty of time to lock to it.



Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #257 on: February 12, 2021, 03:04:59 am »

I got 5x 2764 EPROMs here, marked Texas Instruments TMS 2764-20JL   LHP 8831   ... eBay.

The weird thing is, I can program them and verify them in the programmer.  But they don't work in the controller board!?!

I then tried erasing the old EPROMS in my brand new el-cheapo EPROM eraser.  1/2 hour was enough to erase the chips, next time I'll try 20 minutes and see how good the lamp is...

I then programmed the old EPROMS with the version 506/607 software -  success!  Meter started right up.

Is there anything I could be doing wrong with the TI EPROMS that would make them verify on the programmer, but not run in the actual circuit?



 
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Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #258 on: February 12, 2021, 03:07:49 am »
I also gave up on the '!' for the time being, since it did not run reliably. After two hours or so (with roughly a million of readings) i would find 0D and 0A in the binary data where it doesn't belong.[...]

Couldn't that happen accidentally, if the voltage happens to have 0D 0A in the measured value?
 

Offline srb1954

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #259 on: February 12, 2021, 06:30:18 am »

I got 5x 2764 EPROMs here, marked Texas Instruments TMS 2764-20JL   LHP 8831   ... eBay.

The weird thing is, I can program them and verify them in the programmer.  But they don't work in the controller board!?!

I then tried erasing the old EPROMS in my brand new el-cheapo EPROM eraser.  1/2 hour was enough to erase the chips, next time I'll try 20 minutes and see how good the lamp is...

I then programmed the old EPROMS with the version 506/607 software -  success!  Meter started right up.

Is there anything I could be doing wrong with the TI EPROMS that would make them verify on the programmer, but not run in the actual circuit?
Have you checked that the EPROM programmer set-up is correct (voltages, pulse widths etc) for the TMS2764?

If the parameters are not quite right the programming might be marginal enough that the data verifies correctly immediately after programming but fails later under slightly different conditions. Most good EPROM programmers try to weed out marginal programming by re-verifying the data under high and low Vcc conditions. A cheap programmer might not do that.

You could check the data retention by setting the EPROMs aside for a day and then re-verifying to see if any bits have decayed.

Lastly you should consider whether the chips purchased via eBay might be counterfeit or production rejects that have been relabelled as a different speed grade.
 
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Offline garrettm

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #260 on: February 12, 2021, 07:09:38 am »
I reworked the 3-byte, 22bit fixed point to 64bit floating point conversion since I neglected to perform the two's complement for negative values. :palm:

Unions and structs make this look slick and allow for easy code modification. Do note that there are byte boundary limititations with structs that can cause errors in what would otherwise look like valid code.

Two's complement conversion must be done using the entire 22bit word which was thankfully pretty simple to do using another member inside the union. Note that the error bit is used as a sign bit since they are identical when the ADC has no errors. (Checking for overflow first guarantees this.)

If anyone wants to test it, throw the following code into https://www.jdoodle.com/online-compiler-c++/ and edit the b_data binary values as indicated in the code comments.

Code: [Select]
#include <iostream>
#include <inttypes.h>

typedef union {
  struct {
    uint32_t f :20; // fraction bits
    bool     i :1;  // integer bit
    bool     e :1;  // error bit
    bool     s :1;  // sign bit
  };
  uint32_t   w :22; // 22bit word for two's comp. conversion
  uint8_t    b[3];
} adc_t;

typedef union {
  struct {
    uint64_t m :32; // mantissa (32bit offset)
    uint32_t f :31; // mantissa + exponent
    bool     s :1;  // sign bit
  };
  double     r = 1; // set mantissa bits to 0
} b3fp64_t; // 3-byte binary to FP data structure

//dummy data for testing
uint8_t b_data[3] = {0b11110111,  // 1st byte
                     0b10111111,  // 2nd byte
                     0b11111111}; // 3rd byte

int main() {

adc_t raw; // data stucture for working with raw ADC output

//acquire 3-byte binary data
for (int32_t i=sizeof b_data-1; i>=0; i--) {
  // code for data acqusition...
  raw.b[i] = b_data[sizeof b_data-1-i];
}

// ADC overflow check
if (!raw.s == raw.e) {
  //return 0; // same error value as 5 and 6-byte binary data
  std::cout << "ADC OVERFLOW" << std::endl;
}

// perform two's complement if sign bit == 1
if (raw.s) {
  raw.w = ~raw.w + 1;
}

b3fp64_t val; // unscaled floating point value

val.f |=  raw.f; // fraction bits,        b0-b19
val.r -= !raw.i; // int portion / FP exp, b20
val.s  =  raw.s; // sign,                 b21

std::cout << "FP value = " << val.r << std::endl;
}


*Made some minor improvements to the code: Merged all fraction bits into a single operation and removed a struct for code simplicity.
« Last Edit: February 13, 2021, 03:57:04 pm by garrettm »
 
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Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #261 on: February 12, 2021, 08:25:11 am »

I got the EPROMS working by programming them multiple times with the same data...   They are probably just getting old and cranky.  The Intel EPROMs from the same era seem to not have this issue, they worked reliably first time on the cheapo programmer.

Bottom line - all units are now on the latest firmware, even if something that should have been a simple job ended up taking half the night!  :D




 
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Offline garrettm

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #262 on: February 12, 2021, 09:30:13 am »
...
While waiting for the AB-25 to arrive, i am using our two Flukes with "S2", at about 10 readouts per second and calculating averages every 320 samples.
...
Regards, Dieter

Dieter try using S5 sampling, it acquires samples and outputs them with the least amount of processing delay (reaching 97% sample/average to reading throughput efficiency). See "AVG Processing Delay" in the table below and the updated Excel spreadsheet. Your 8502A might have a different optimal sampling setting than my 8506A, but the concept still holds.

This way, you should have effectively "more" samples per individual reading from the DMM for the same effective number of samples when averaging at the PC.

Code: [Select]
Sampling	Reading		AVG Digitizing		AVG Processing	Digitizing
Exponent Period Time / Sample Delay         Period
0         52.2         52.20         48.03         4.17
1         55.2         27.60         46.87         8.33
2         60.3         15.08         43.63         16.67
3         68.8         8.60                 35.47         33.33
4         89.4         5.59                 22.73         66.67
5         137.5 4.30                 4.17         133.3
6         270.9 4.23                 4.23         266.7
7         537.7 4.20                 4.37         533.3
8         1071 4.18                 4.33         1067
9         2140 4.18                 6.67         2133
10         4273 4.17                 6.33         4267
11         8540 4.17                 6.67         8533
« Last Edit: February 12, 2021, 09:36:17 am by garrettm »
 
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Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #263 on: February 12, 2021, 03:03:53 pm »

@Dietert,  do you know what firmware revision is in your 8502A units?

I have an 8502A here that says 2.0.8 on startup.

 

Offline dietert1

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #264 on: February 12, 2021, 04:10:35 pm »
One of our Fluke 8502A runs firmware 2.0.3, the other one 3.0.0.
Today i learned how to exercise both input relays K1 and K2 on startup, cycling through "VA,R1," then "V,R2," then "V,R3,".

Regards, Dieter
 
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Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #265 on: February 13, 2021, 12:27:10 am »
I took a closer look at seeing if I could improve the serial port hardware.    It appears that while the receiver is interrupt driven, the transmit is polled.  The UART doesn't have any sort of FIFO and will set a flag when the byte is transferred to the serial register.  So their firmware is stuck polling this flag and sending one byte at a time.   Even if the hardware were improved, the firmware would have to be rewritten to support it.  The easiest thing if the firmware could be modified would be to change the polling time but I suspect that would cause more problems.   

Oh well.   I did add support to read and decode the status.   Shown with a 10Hz sinewave.   




Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #266 on: February 13, 2021, 04:24:20 pm »
Vishay 10k ohm foil resistor.  Using 4-wire mode.  Roughly 12 hours of data collected with the meter sitting out in the open.   Plotting the mean for the last 6 hours.   

https://www.mouser.com/datasheet/2/428/zseries-1022194.pdf

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #267 on: February 13, 2021, 04:38:56 pm »
Looks good @joeqsmith!

Do you log temperature as well?  Could be interesting to see how that influences the meter.  I'm pretty sure they all behave differently!
« Last Edit: February 13, 2021, 04:43:41 pm by SilverSolder »
 

Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #268 on: February 13, 2021, 05:06:15 pm »
I have a meat packing box that I use for temperature experiments but it's not large enough to place the meter into.   

I plan to restart the test with a lower value resistor.   If I measured the temperature, where would you think the most useful place would be to measure it? 

***
Looking through my stash, I thought I may have had a spare thermistor but no luck.  I do have one of those Fluke K-type adapters.   I could clip it next to the resistor with some foam to try and shield it from the air currents.   Not a great setup but better than nothing.   Let me know what you want to see.
« Last Edit: February 13, 2021, 06:00:29 pm by joeqsmith »
 

Offline dietert1

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #269 on: February 13, 2021, 08:44:24 pm »
As far as i understand, your test resistor drifted about 2 ppm. This is completely normal for those foil resistors. Sometimes you have to wait several days for those foil resistors to settle. You can see similar measurements here:

https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg2751598/#msg2751598

Regards, Dieter
 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #270 on: February 13, 2021, 08:46:08 pm »
It could be interesting to see the temperature inside the R2 A/D converter, as well as the temperature next to the resistor being tested?

Assuming the temperature in the lab moves a little bit, and drafts of air are switched on and off with the central heating (even if the temperature doesn't change, the amount of heat that is carried away does change)...  we may see some interesting correlations?
 

Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #271 on: February 13, 2021, 09:20:22 pm »
Yes, the whole setup (meter + resistor) drifted about 2ppm.   Guessing that mostly the meter.

I changed it over to a Vishay S series, 50 ohm 0.01% part. This particular part is a C material.   

http://www.vishaypg.com/docs/63001/63001.pdf

I just soldered it to a couple of copper strips and clamped the K-type sensor to it.   The meter was not zero'ed and it's reading a bit on the high side.  (50 +/-0.005 ohms  plus the meter's 0.003%+1.4).   Keep in mind also, this was a poor man's alignment.  I don't have the tools needed to do a proper job. 

It's been running like this for about 2 hours.    Normally I would toss a beach towel over it but like before, its just sitting out in the open.

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #272 on: February 13, 2021, 10:14:57 pm »

I like the temperature sensor clamping arrangement! 

Might just have a similar "Thermal Probe Mounting Adapter, $673" somewhere here! :D
 

Offline joeqsmith

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #273 on: February 13, 2021, 11:17:40 pm »
Those paper clips come in handy for all sorts of things.  Soldering, gluing, holding wires in place, mounting sensors...   

I don't think you will learn much from this test.  It's been running about 3.7 hours.  The temperature has continued to go up during this time about 1deg C.  The spikes I suspect are static discharges in the room.  You can tell when I was no where near the setup.   The measured resistance however has stayed relatively constant.   

I have a higher tolerance part that I would like to try and use with better mounting.   I plan to zero out the meter this time and see if it can actually get some numbers that are within the total tolerance.     I'll move the thermocouple to the center of the meter.

Some of the better handheld meters I've looked at measuring this part.   



 

Offline SilverSolderTopic starter

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Re: Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
« Reply #274 on: February 14, 2021, 12:22:15 am »

The temperature swings look like a central heating system cycling - Do you have an oil or a gas furnace by any chance?


 


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