INFO - Scored this Keithley 191 multimeter on eBay

[ivan747]

I'm quite sure it is good value for the $80 bucks I spent. I haven't seen much Keithley stuff on this forum apart from Dave's nano-amperic and kilo-volt sources  Check it out, the Keithley 191 from 1979:

http://www.ebay.com/itm/Keithley-191-Digital-Multimeter-/380544981240?pt=LH_DefaultDomain_0&hash=item589a3f98f8



My main concern is that it wasn't fully tested, but at least I can see it's reading a voltage:


I see it is on the 2V range. I don't know if -1.8V can be achieved only with noise, but since the Null function is activated, I'm guessing someone nulled it right after some overshoot.

It has 5 and a half digits and has an accuracy far better than anything else I have. There comes my second concern: this might be out of cal. and I won't know it until I get into college and have access to a weston cell or something like that.

Assuming everything is alright, I get a meter with 4-wire measurement, great low level measurement capabilities overall. It will help me a lot in my analog projects. Apparently on this model, AC measurement comes as an option.

No CAT crap on this thing! It has proper banana jacks, and they accept anything from multimeter leads to spade terminals. It is quite 70's vintage  O0

I managed to get a hold of the manual from Keithley themselves, it's good to see they do that. 
Here are the specs:

• 5 and a half digit resolution (200k count)
• Manual ranging
• Goes down to 1uV and 1m-ohm (milli)
• 4-wire measurement function (very handy for me)
• Nulling function, of course
• Interestingly enought, there's no current measurement
• 0.005% ±2 digit basic DC accuracy

That's quite remarkable for the price I paid, I think. I can do current measurement with a shunt. Jeez, I can build and calibrate my own uCurrent with this thing! 

Share your thoughts with me, I want to hear your opinion! (specially if I wasted my money )
-Ivan

Edit: here's the manual:
https://dl.dropbox.com/u/17276290/191%20%28A%20-%201979%29%2830183%20Instruction%29.pdf
Edit 2: made the title comply with "standards" 

P.S. It is the first time I get to use the nerdy smileys that's why I used to many!

[ve7xen]

I've been looking for a decent bench meter for a while and always pass right over these 70s vintage ones because most of them have worse accuracy and resolution than my handheld meters, so even minimal investment isn't really worth it.

With this one however you seem to have got a gem at a great price. A 5-1/2 digit with 0.005% accuracy and the good low range features for $80 delivered is a pretty good deal IMO. My experience with test equipment from the 'bay is that if it works reasonably, it's usually pretty close to in cal, if not bang on. When stuff is out, it's way out or doesn't work at all. This particular one isn't even sold as 'for parts', they're offering a DOA warranty.

I guess it won't take modern shrouded test lead jacks? Might have to replace or modify the ends on some or something.

You could sample or buy a 0.05% voltage reference and some precision resistors as a sanity check on the calibration, but calibrating this in a hobby lab is going to be out of reach of most.

Nice find, and I'll now keep my eyes open for the Keithley 191 in my search. Keep us posted once you've had a chance to make a few measurements.

[Smokey]

I scored a Keithley 175 a while back.  Gotta love ebay.  Worked great and surprisingly modern looking inside.  Everything except for that stupid fixed power cable coming out of the bottom like on Dave's 480.
There's actually a whole lot of Keithley love on the forum.  They made some good stuff back in the day.  Still do even though they got bought by the evil Danaher overlords.  I love how the wikipedia article words it:
"In September, 2010, the company agreed to sell itself to the Danaher Corporation"
The company sold ITSELF!!

[ivan747]

...

I guess it won't take modern shrouded test lead jacks? Might have to replace or modify the ends on some or something.

You could sample or buy a 0.05% voltage reference and some precision resistors as a sanity check on the calibration, but calibrating this in a hobby lab is going to be out of reach of most.

Nice find, and I'll now keep my eyes open for the Keithley 191 in my search. Keep us posted once you've had a chance to make a few measurements.

As for shrouded leads, I can plug them into banana jacks if I screw the cap out, no problems with that.

I could buy one of those voltage references, but I need to read a lot before trying to calibrate my equipment. I spent most of my money on this, so those will have to wait.

And remember guys, keep your eyes open for Kethley, they were way ahead their time. I have come to the conclusion that all the things they produced are still useful today.

I scored a Keithley 175 a while back.  Gotta love ebay.  Worked great and surprisingly modern looking inside. Everything except for that stupid fixed power cable coming out of the bottom like on Dave's 480.

There's actually a whole lot of Keithley love on the forum.  They made some good stuff back in the day.  Still do even though they got bought by the evil Danaher overlords.  I love how the wikipedia article words it:
"In September, 2010, the company agreed to sell itself to the Danaher Corporation"
The company sold ITSELF!!

I hate fixed power cables, but at least the pawn shop doesn't keep the power cord  . I know I shouldn't but I am starting to dislike Danaher just for being themselves.

[alm]

I think $80 is a fair price for this meter, assuming it is working.

I see it is on the 2V range. I don't know if -1.8V can be achieved only with noise, but since the Null function is activated, I'm guessing someone nulled it right after some overshoot.

The input impedance is > 1 Gohm for the ranges up to 2 V. This high input impedance makes it extremely sensitive to noise. Try calculating how much current it would take to induce 2 V across the 1 Gohm input impedance.

It has 5 and a half digits and has an accuracy far better than anything else I have. There comes my second concern: this might be out of cal. and I won't know it until I get into college and have access to a weston cell or something like that.

Don't be surprised if it's still in spec, I don't have experience with this particular meter, but it's rare for good bench meters to drift far outside their specified accuracy range, unless something breaks.

[ivan747]

That explains the high voltage on the 2V range. 1.8V/1x10ˆ9 = 1.8x10ˆ-9. That's just a nanoamp. Great 

[EEVblog]

The specs are nothing to be sneezed at!

Dave.

[ivan747]

I find the specs very good, but this meter lacks functions. Without any accessories, it only measures volts and ohms. I hope I am getting the AC option here. The rest can be done with other multimeters. I mean, nobody needs to measure rectifier diodes with 5 1/2 resolution nor one expects the capacitance function to match the accuracy of an LCR meter.

[alm]

This was quite common for high precision bench meters back in the day. ACV was often optional, on some Flukes even Ohms was optional. They usually lacked current ranges; Fluke sold a box with external shunts and ganged switches that would fit in a rack together with the DMM.

[olivil]

I recently scored a similarly specced Fluke 8810A with the same banana jacks for 35$ and I was wondering if it was safe to remove the shrouding off a set of good test leads to use with these kinds of plugs? I kind of like the idea of being able to "screw" stuff to the terminals (so I'd prefer not to remove the caps to accept shrouded leads, though if that's the only choice, so be it!).

Do they even make "good" quality test leads with simple banana jacks anymore? (the cheap Chinese ones on eBay are the only kind I found...)

[Bored@Work]

Do they even make "good" quality test leads with simple banana jacks anymore? (the cheap Chinese ones on eBay are the only kind I found...)

Pomona makes some. You will find they give them a low voltage rating because of the plugs.

[alm]

Plugs with a retractable sheath allow for some protection even with traditional banana jacks. Pomona also makes test leads with them. They're somewhat rare and expensive, however.

[ModemHead]

Do they even make "good" quality test leads with simple banana jacks anymore? (the cheap Chinese ones on eBay are the only kind I found...)

Probemaster will put just about any termination you want on a set of DMM leads, including the retractable sheath.  I don't have firsthand experience with Probemaster leads, but I have heard they're quite decent.

[david77]

How about putting the plugs you like onto a set of leads you like? Like soldering them yourself? 

I quite like these:

[Stephenniall]

I use these Hirschmann test leads, They're absolutely brilliant. The sillicone on the wire is flexible, and they're unsheathed. You can get the matching probes which plugs into the end.

http://uk.rs-online.com/web/p/4-mm-connector-test-leads/0488416/

[ivan747]

The ProbeMaster ones don't look any bad at all! The price is quite good, $15. But they sell a whole kit for that series. Maybe it is the solution for Olivil and I.

I was thinking we could make adapters as well, but that's hard to do properly. I also can replace the binding posts in the multimeter, if there is space inside for a recessed input jack.

[ivan747]

Just a heads up. THe multimeter has arrived! In the same condition I expected it to be in. It was manufactured in 1981, apparently. I left it warming up for a while. I will need the ProbeMaster probe or some modded probes to remove the shrouding, as Olivil suggested. Expect a review coming soon. 

[nanofrog]

Probemaster offers their lead sets with multiple banana styles, including unsheathed or retractable (either would work for that meter).

[alm]

I was thinking we could make adapters as well, but that's hard to do properly.

There are adapters that convert from shrouded to unshrouded banana plugs. Pomona makes them, and I think Frankie (iloveelectronics) also sells them.

[silicon_ghost]

Do they even make "good" quality test leads with simple banana jacks anymore? (the cheap Chinese ones on eBay are the only kind I found...)

Probemaster will put just about any termination you want on a set of DMM leads, including the retractable sheath.  I don't have firsthand experience with Probemaster leads, but I have heard they're quite decent.

I own a Probemaster shrouded M/M banana plug kit (plus a large set of adapters) and a selection of cables.  Very high quality IMHO.  I highly recommend them as a less expensive alternative to something like Fluke cables.  Definitely not as cheap as the Chinese WanHungLo brands.