Author Topic: Keithley 197A owners' corner  (Read 7685 times)

0 Members and 1 Guest are viewing this topic.

Offline Kinkless Tetrode

  • Regular Contributor
  • *
  • Posts: 57
  • Country: us
  • Country: us
  • Vacuum Tube enthusiast, Voltnut, and Timenut
Re: Keithley 197A owners' corner
« Reply #75 on: June 16, 2019, 09:47:37 am »
Hi all, I'm a new proud owner of a couple the Keithley 197 (Military Version AN/USM-486A) units.  I bought them from a seller who must have got them from a military surplus auction, and other than some desert dust on them, they are both in great condition.  I don't know if and when they were last calibrated, but the two units read very closely to each other; within about 10 mV on the 200 mV range.

Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.
« Last Edit: June 16, 2019, 10:06:36 am by Kinkless Tetrode »
Whilst others count beans, I count electrons, and photons too.
 

Offline rastro

  • Frequent Contributor
  • **
  • Posts: 353
  • Country: 00
  • Country: 00
Re: Keithley 197A owners' corner
« Reply #76 on: June 16, 2019, 02:36:29 pm »
...
Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.

Congratulations on your purchase. 

I am not sure about the history of the 197 line but here are some observations:
- Based on the technology the military model came out after the original 197/A models
- The 197M(AN/USM-486A) shows a date of December 1994.
- Last year I came across two 197A models that did not have back light but had the new processor like the military mother board but without the 10A current fuse.  Date on the that motherboard was 1992.
- I bought my initial 4 military models about 5 years ago new old stock from an auction house - this was an uncommon find at the time.
- In the last 2 years I've seen more military models showing up on ebay; usually new/lightly used.  Probably the US govt getting around to purging old stock.

Anyway I think the military model is the best choice if you don't need the back-light or GPIB option.

rastro

« Last Edit: June 16, 2019, 02:39:29 pm by rastro »
 

Offline Kinkless Tetrode

  • Regular Contributor
  • *
  • Posts: 57
  • Country: us
  • Country: us
  • Vacuum Tube enthusiast, Voltnut, and Timenut
Re: Keithley 197A owners' corner
« Reply #77 on: June 16, 2019, 10:05:17 pm »
...
Does anybody have any idea how common this military model is compared to the regular 197/A models?  Or, how long they were in production?  Other than the references given earlier in this thread, I really don't see anything mentioned about them on the internet.

Thanks.

Congratulations on your purchase. 

I am not sure about the history of the 197 line but here are some observations:
- Based on the technology the military model came out after the original 197/A models
- The 197M(AN/USM-486A) shows a date of December 1994.
- Last year I came across two 197A models that did not have back light but had the new processor like the military mother board but without the 10A current fuse.  Date on the that motherboard was 1992.
- I bought my initial 4 military models about 5 years ago new old stock from an auction house - this was an uncommon find at the time.
- In the last 2 years I've seen more military models showing up on ebay; usually new/lightly used.  Probably the US govt getting around to purging old stock.

Anyway I think the military model is the best choice if you don't need the back-light or GPIB option.

rastro




Rastro, Thanks for your insightful observations.

Also, I notice that on the bottom of our units there is some US Gov't contract information. My unit says "contract daah01-92d-0031" and since gov't contracts are public information, we might be able to get a bit more information on the 197-M series from government archives.  Hmm...this makes me very curious...

A Google hit shows that an M model, with case and probes, was sold on eBay late last year for $360.  So it looks like there are a few floating around. And I completely agree, it's a really great portable/bench 5.5 digit unit.  I really like the extra shielding and toroid upgrade.

KT
« Last Edit: June 16, 2019, 10:27:25 pm by Kinkless Tetrode »
Whilst others count beans, I count electrons, and photons too.
 

Offline Brian of Romsey

  • Contributor
  • Posts: 9
  • Country: gb
  • Country: gb
Re: Keithley 197A owners' corner
« Reply #78 on: July 22, 2019, 11:05:39 pm »
Re: Replacement display technology.

I have been pondering this today.  I would assert that there are no suitable OLED displays easily available.  There are tiny ones but nothing with the sort of size needed to replace the existing display.

There also don't seem to be any TFT LCDs with the right sort of aspect ratio.  By the time you get to something wide enough, they are way too tall for the case and also getting quite expensive.

It's my opinion that the best replacement is LED displays.  But even this is hard and by no means perfect.  The readout needs a small text field on the left (Auto, Rel, dB, Stor, Recl, Bat, etc), a 7-segment numeric field for the value, including a leading minus sign (seven displays), and a small text field on the right (multiplier, units, and maybe "AC").  I think that the text fields can be handled by 5x7 displays.  Either two VQC10, two HDSP-2000, or eight TIL305 displays.  Maybe even HDSP-2113.



 

Offline rastro

  • Frequent Contributor
  • **
  • Posts: 353
  • Country: 00
  • Country: 00
Re: Keithley 197A owners' corner
« Reply #79 on: July 23, 2019, 01:08:25 am »
Re: Replacement display technology.

I have been pondering this today.  I would assert that there are no suitable OLED displays easily available.  There are tiny ones but nothing with the sort of size needed to replace the existing display.

There also don't seem to be any TFT LCDs with the right sort of aspect ratio.  By the time you get to something wide enough, they are way too tall for the case and also getting quite expensive.

It's my opinion that the best replacement is LED displays.  But even this is hard and by no means perfect.  The readout needs a small text field on the left (Auto, Rel, dB, Stor, Recl, Bat, etc), a 7-segment numeric field for the value, including a leading minus sign (seven displays), and a small text field on the right (multiplier, units, and maybe "AC").  I think that the text fields can be handled by 5x7 displays.  Either two VQC10, two HDSP-2000, or eight TIL305 displays.  Maybe even HDSP-2113.

Yes it's difficult to find a good functional fit to replace the old LCD display.
I believe several of the display suggested are obsolete or difficult to readily source (VQC10, HDSP-2000, TIL305).
You also need to consider part costs.  The HDSP-2113 is available but in small quantities costs $37.00 from mouser.

Dave Jones did a thread/video on making custom LCD's.  This could be a direct replacement for a leaky/broken LCD.  The difficulty is there is a fair amount of up front setup costs and design effort to duplicate a replacement.  You would need to get enough sponsors sharing the cost to make this route feasible.  Then there is also the problem of getting new zebra connectors to replace 30 year old ones just hanging on.  Probably not going to get off the ground.

Another solution I thought about is making a PCB that replaces the current display board (same size) but has SMD LEDs replacing the LCD along with a plastic template/screen for symbols/words.  Getting the double sided (?) PCB produced in small quantities would be reasonable.  However soldering all those SMD LEDs would be certainly be a labor of love.  However I think this would be the cleanest and most attainable solution.  It would also upgrade the K197(brown) to better viewing than a K197A(grey) with LCD/back-lighting.  Lot's of work on PCB design routing the drivers and probably programing a controller for display generation.  Once complete it could also be adapted for other Keithleys of that series.  Wish I had time to start something like this...

rasto
 

Offline Brian of Romsey

  • Contributor
  • Posts: 9
  • Country: gb
  • Country: gb
Re: Keithley 197A owners' corner
« Reply #80 on: July 23, 2019, 07:52:29 pm »
Rasto,

  I agree on the price of things for an in-case solution.  Perhaps an out-of-case solution would work with some sort of new display, probably a 3.5" TFT LCD in a little case with a cable to the 197A.  Portrait mode, status indicators at the top, big numerical value right across with units at the right, and then maybe an analogue 'meter' at the bottom.

      https://www.aliexpress.com/item/32609807497.html?spm=a2g0o.productlist.0.0.1b7a5e359o85W8&algo_pvid=6e1ec20b-de25-421a-91cc-a95b11ceb965&algo_expid=6e1ec20b-de25-421a-91cc-a95b11ceb965-6&btsid=42aa5706-d76b-47e8-9567-bc3062ca7320&ws_ab_test=searchweb0_0%2Csearchweb201602_6%2Csearchweb201603_52

  The other (remote) possibility for the in-case solution is whether a couple of these:

      https://www.aliexpress.com/item/32801200578.html?spm=a2g0o.productlist.0.0.5e9b3b27Vdioca&s=p

could be brought close enough together horizontally and made to work.

  Cheers, Brian.

 

Offline rastro

  • Frequent Contributor
  • **
  • Posts: 353
  • Country: 00
  • Country: 00
Re: Keithley 197A owners' corner
« Reply #81 on: July 23, 2019, 09:12:41 pm »

Maybe extend the out-of-case-display concept using an ESP8266/ESP32 to extract the readings/status from the K197 and use the WIFI to access a simple server on the module displaying the DMM data.  Then you have an unlimited choice of WIFI connected displays (phone/tablet/PC).  I think you can get an ESP8266 for under $5.00.

I'm not an expert on the ESP's but it seems feasible according to other projects I have seen using these modules. 

rastro
 

Offline Brian of Romsey

  • Contributor
  • Posts: 9
  • Country: gb
  • Country: gb
Re: Keithley 197A owners' corner
« Reply #82 on: July 23, 2019, 10:24:25 pm »
Hi,

The idea of Wi-Fi or Bluetooth and an ESP had occurred to me.  I hadn't thought of an internal webserver to be honest.

I am aware that there are existing (modern) DMMs and such like that do some sort of BT protocol for remote displays.  Given how much trouble Dave reported getting the BT thing working with his recent DMM I figured that that was a path to a whole heap of pain.

Cheers, Brian.
 

Offline Brian of Romsey

  • Contributor
  • Posts: 9
  • Country: gb
  • Country: gb
Re: Keithley 197A owners' corner
« Reply #83 on: August 10, 2019, 07:33:55 pm »
Hi,

  Found a possible SPI OLED display: https://www.aliexpress.com/item/32988174566.html

  With a resolution of 256 by 64 that would be sufficient for sign, value, & units in the top third of the display and all the rest of the possible status bits and bobs along the bottom third.

  Cheers, Brian.
 

Offline Brian of Romsey

  • Contributor
  • Posts: 9
  • Country: gb
  • Country: gb
Re: Keithley 197A owners' corner
« Reply #84 on: August 12, 2019, 12:59:19 pm »
Hi,

This is an instrument display replacement strategy.  It may be instructive for a 197 or 197A display replacement.

Brian.
 

Offline electrold

  • Newbie
  • Posts: 3
  • Country: us
  • Country: us
Re: Keithley 197A owners' corner
« Reply #85 on: September 13, 2019, 06:01:15 pm »
     I just received the AN/USM-486A military model of the Keithley 197 multimeter which I purchased on eBay. It came with its carrying case, IEC line cord, test leads, and RF probe. It has the battery and looks new. It powered up fine and some preliminary checks give me confidence that it will perform as it should. This model has the battery option and the rear panel CALIBRATION switch.
      One thing I observed from reading the military manual and the Keitlley manual is that the military model has relaxed accuracy specs. For example, the Keithley 197 spec for the 2VDC range is 0.011% +2 counts for 1 year, whereas the military spec is 0.05% +10counts for 1 year. Other specs are similar with the Kiethley having the better specs. I don't know if the Keithley model is actually better or if the military has just loosened their required specs. If anyone has any knowledge about this I would appreciate a reply.
 

Offline rastro

  • Frequent Contributor
  • **
  • Posts: 353
  • Country: 00
  • Country: 00
Re: Keithley 197A owners' corner
« Reply #86 on: September 13, 2019, 10:04:20 pm »
I haven't dug into it, but did you take in account for the environmental range expectation on the "M" version?
 

Offline electrold

  • Newbie
  • Posts: 3
  • Country: us
  • Country: us
Re: Keithley 197A owners' corner
« Reply #87 on: September 14, 2019, 11:36:41 am »
Environmental specs are identical on commercial and military versions according to the manuals. I do find a difference in warm-up times though. The commercial 197 has 1 hour warm-up to rated accuracy but the military 197M has a warm-up time of 5 minutes. Perhaps this is the reason for the relaxed accuracy spec on the 197M. If it is operated on battery, you can't wait around for an hour for it to settle down to the better accuracy.
 

Offline rastro

  • Frequent Contributor
  • **
  • Posts: 353
  • Country: 00
  • Country: 00
Re: Keithley 197A owners' corner
« Reply #88 on: September 14, 2019, 02:41:54 pm »
You're probably right about the 5-minute warm up needing 'relaxed' specifications.  Most likely the 'M' version is probably on par with the standard K197 if you allow a full hour warm up.

As mentioned before I still prefer the 'M' version because it has an added fuse on the 10 Amp input and removable power cord.  It also looks like it has better noise shielding.

rastro
 

Offline electrold

  • Newbie
  • Posts: 3
  • Country: us
  • Country: us
Re: Keithley 197A owners' corner
« Reply #89 on: September 14, 2019, 04:23:18 pm »
The battery in my meter was, of course, discharged and could not be charged as 5 of the 10 cells in the pack were unchargeable. Who needs battery operation for this anyhow? Certainly I don't - so I removed the pack and the battery board.
My meter has a CAL sticker on it - it was last calibrated Dec 2, 2016 and has a cal void date of Mar 22, 2019. Using my A584-M Voltage Reference Module with the meter warmed up for more than an hour, it is well within the 197 commercial specs, at least at 2.5, 5, 7.5, and 10VDC.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf