EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: AlphZeta on January 15, 2013, 03:36:42 pm
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I have been looking for a bench multimeter for a while. I know that HP3478A is highly touted by Dave and many forum members, and don't get me wrong, I think it is an excellent piece of equipment as well.
But What I needed is a bench meter that can measure low voltage and current at a relatively high resolution and can do kelvin resistance measurement. So when an eBay auction came around for this Keithley 196 6 1/2 digit DMM (http://www.ebay.com/itm/321056223365?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 (http://www.ebay.com/itm/321056223365?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649)) I jumped right at it. I just couldn't resist the price point.
Anyway, it's coming this Saturday and I can't wait to get my hands on it. I will definitely put some pictures here once I get it. I may decide to do a review of it on my site as well....
Anyone has a Keithley 196 and want to share your experience?
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Here's the specs for those who don't want to dig up the manual:
DC VOLTS
300mV (100nV resolution) to 300V (100uV resolution)
AC VOLTS
300mV (1uV resolution) to 300V (1mV resolution)
OHMS
300 Ohm (100 micro Ohm resolution) to 300 mega Ohm
AC/DC AMPS
300 uA (1nA resolution) to 3A (burden voltage 0.4/0.5V between 300uA to 300mA)
READING UPDATE RATES (per second)
9 (6 1/2 digit) to 1000 (3 1/2 digit)
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Here's the manual:
http://institute.unileoben.ac.at/physik/Praktikum/Manuals/Keithley_196_DMM.pdf (http://institute.unileoben.ac.at/physik/Praktikum/Manuals/Keithley_196_DMM.pdf)
Great specs, that one's better than the 191 I ordered. :-DMM
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I like the fairly closely related model 199. The big LED display is very nice, especially compared to the crappy LCD without backlight that the 3478A uses. The 196 has offset compensated ohms measurements (compensates for offset voltages), which is fairly rare. It was designed to compensate for thermal offsets. Should be a very nice meter, definitely a step up from the 3478A.
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Yeah, I downloaded the manual already :) I wish all the manuals nowadays are as detailed as they were decades ago...
Anyway, the only thing about 3478A I didn't quite like is the calibration data-stored-in-RAM thing. While the Lithium battery on board is guaranteed to last the designed service life (10 to 15 years), and it is not that difficult to change the battery while leaving the unit powered on just the idea of that the data could be lost due to a battery failure makes me nervous. Of course, I suppose it was the state-of-art technology back then.
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OK. Just received the unit. Did a quick check and everything appeared to be working. The following picture is taken using a 10V voltage standard. Not sure when the last calibration was done on this unit, but seemed have not drifted too much. The probes came with the Keithley 196 are pretty decent, rated for CAT III 1000V. But I doubt that these were the original leads. The brand of the probes seems to be "Probe Master" (http://www.probemaster.com/product_info.php?cPath=2_12&products_id=198 (http://www.probemaster.com/product_info.php?cPath=2_12&products_id=198))
I will open it up and take a look inside and snap more pictures later.
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Now more pictures.
There are two circuit boards and it is not the easiest to remove them because some of the front panel wiring is soldered directly on to the top board. Anyway, here are the pictures:
(the two socketed ICs are OP01, a high speed inverting op amp and an AD637 which is a precision RMS-DC converter)
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A few more
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It seems like a nice DMM but its pretty old. Judging from the date codes its build somewhere in 1987 / 1988. I'd backup the EPROM just to make sure.
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It seems like a nice DMM but its pretty old. Judging from the date codes its build somewhere in 1987 / 1988. I'd backup the EPROM just to make sure.
That brings up a good point @nctnico. I thought these NMOS EPROMs are spec'd to retain data for at least 100 years?
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Apart from certain MOSTEK EEPROMs (used in some HP and Tek products like the HP 3456A) that had manufacturing defects, EEPROMs generally seem to last a very long time. I'm sure there is a small chance for them to fail, but it's not like EEPROMs in instruments from the late eighties are failing in droves.
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I worked with equipment that was built in the 1970's ( at latest) which used 2708 eproms. Never had a fault on those boards where the 14 eproms were other than the capacitors going open circuit. They worked even with no capacitors, they were just replaced and found to be open during a blanket change of that particular capacitor as most had failed after 30 years of toasting. No covers either on the chips, enclosed in a hermetic enclosure.
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Not the most aesthetic looking line of meters but still excellent performers. I have 2 of the 195's at home, (one with the AC option the other without.).
I would love to get my hands on the aging 196 at work !. Still being used in an old monitoring setup running 24/7. :(
I have done repairs to the old timer due to the transformer leads being trimmed too short at assembly thus not making a solid
mechanical/electrical joint at the PCB. Result 'dry joints' from thermal cycling which caused charring of the PCB at the pad (can't remember which tap on the secondary though). I highly recommend while you have it apart (still?) that you check and re solder the transformer pads.
Enjoy
LowZ
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I highly recommend while you have it apart (still?) that you check and re solder the transformer pads.
I did a quick check on the solder joints, everything appeared to be Okay. The only things that have shown their age are those plastic standoffs. The plastic had aged so much during the years and they became quite brittle. Small pieces would just come off if you press on it. But this is not unusual for plastic stuff made back then. Not a big deal.
I had a laptop from 1995 and when I tried to repair it a few months back, I had found that the plastic was all cracking....
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I do not know this meter, but its very likable for function and up keep. Its easy to access and work on, very generic parts, no unobtanium I can see in the manual other than the firmware, and specs better than most bench meters, and just below that of a system DMM like the 3457a. Meters of that era, including the 3456a or -7a are not CAT rated, just keep in mind when being used.
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I worked with equipment that was built in the 1970's ( at latest) which used 2708 eproms. Never had a fault on those boards where the 14 eproms were other than the capacitors going open circuit. They worked even with no capacitors, they were just replaced and found to be open during a blanket change of that particular capacitor as most had failed after 30 years of toasting. No covers either on the chips, enclosed in a hermetic enclosure.
AFAIK Eproms are specified to retain their data for 10 to 20 years. You can be lucky but every now and then you see requests from people who would like a copy of the contents of an eprom because their equipment stopped working.
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Not my problem any more...........Gone to South America.
Some of the earlier ones were supposed to last for up to 100 years, at least that was in the data sheets as to max lifetime. They had such big cells and with a 21v programming that charged the cell up they probably would make it. Modern ones like flash are more problematic. Small cells and low charge, you can almost count the electrons now.
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Just took a look at the service manual. I believe that the program (firmware) is stored in the two EPROMs (27128) and the calibration data is stored in the EEPROM (2816A). Unfortunately for 27128 the datasheet does not specifically mention its data retention period. But for the EEPROM 2816, the data retention period is >200 years according to Microchip. I may backup the 27128's just in case....
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This guy (http://www.ko4bb.com/manuals/index.php?dir=04)_ROM_Images_and_Drivers (http://www.ko4bb.com/manuals/index.php?dir=04)_ROM_Images_and_Drivers)) seem to have the EPROM firmware images for Keithley 196 (B16, mine is B17). He/she has firmware images for other test gear as well.
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Well, just for the sake of absolute certainty, I took out both of the 27128 EPROMs where the firmware resides and dumped the content out. While I was at it, I also backed up the content of the EEPROM (2816). As it turned out the particular EEPROM used in my Keithley 196 is a KM2816A, and the datasheet states a minimum 10 years of retention period (whereas the same EEPROM manufactured by Microchip is spec'd for 200 years). So now I can sleep at night knowing that in the event I do need to re-flash the EPROM or the calibration data I am covered :D.
Of course, I might never need to resort to the backups since most EPROM/EEPROMs can last way beyond the specified data retention period under room temperature.
For those who need the firmware image, here you go: http://www.kerrywong.com/blog/wp-content/uploads/2013/01/Keithley196.tar.gz (http://www.kerrywong.com/blog/wp-content/uploads/2013/01/Keithley196.tar.gz)
Thanks @nctnico for the suggestion!
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Nice pictures. I have 196 too ( and a 199 and 2000) the 199 is a very good meter. I have one that was given to me by a friend who had three. All three giving the same readings and even now, a few years later it is still spot on.
The 196 was fresh calibrated when I bought it.
But if i read all the horrorstorys about eproms i am afrraid i have to find a way to read and write those. But everytime I ask somebody the answer is, there are o many eproms, which one ? So is it true you need a whole bunch of programmers ? I have one, an old one from the 80's, the DOS software is still available but it uses rs232. I have a toshiba T1000,but that has a problem, gound a box of 720K diskettes and a 3,5 diskdrive to build in my computer but now I have to get that all to work. And if I read this sort of storys I think I must hurry. I have 2 x 7,5 digit and 1x 6,5 digit and a 5,5 digit that ould be in the dangerzone. ( and i'm a severe case of digifobia)
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Nice pictures. I have 196 too ( and a 199 and 2000) the 199 is a very good meter. I have one that was given to me by a friend who had three. All three giving the same readings and even now, a few years later it is still spot on.
The 196 was fresh calibrated when I bought it.
But if i read all the horrorstorys about eproms i am afrraid i have to find a way to read and write those. But everytime I ask somebody the answer is, there are o many eproms, which one ? So is it true you need a whole bunch of programmers ? I have one, an old one from the 80's, the DOS software is still available but it uses rs232. I have a toshiba T1000,but that has a problem, gound a box of 720K diskettes and a 3,5 diskdrive to build in my computer but now I have to get that all to work. And if I read this sort of storys I think I must hurry. I have 2 x 7,5 digit and 1x 6,5 digit and a 5,5 digit that ould be in the dangerzone. ( and i'm a severe case of digifobia)
Those EPROM/EEPROM's are parallel ones and are pretty standard. In 196, the the two EPROMs are on the bottom board with labels on them to cover the UV window. And the EEPROM is two chips over to the right. I just used an Arduino with a port expander to read and dump the content. You can find the details on my blog (http://www.kerrywong.com/2013/01/28/keithley-196-firmwarecalibration-data-backup/ (http://www.kerrywong.com/2013/01/28/keithley-196-firmwarecalibration-data-backup/)).
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Those eeproms do die... I swapped one yesterday. Xicor 2864. Write error during calibration of a machine. I was calibrating it and at the last moment it saves the data. And came up with that error. Power cycle and the machine did returned error calibration data corrupt. Popped the lid , put a new one in redid calibration. Perfectly fine now. And its not the first time i see that. The early ones also could only be written a few tens or hundred times before they died.
Making backups is a good idea. Memories will eventually die. I have a 6624 power supplie with a dead eprom.... One of its data lines is permanently stuck to ground.
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I have one of these Keithley 196 meters, from Ebay, which I have been using for recording the voltage of a LTZ1000 voltage reference. Of course, based on the specs the LTZ1k would be more stable than the meter. Anyway, I am logging data via GPIB and plotting the results. I see, for example, 7.23114 V with daily variations of about +/- 5 counts but every so often (maybe 1x or 2x per day) I get a single reading which is maybe 50 counts off the long term average, then it returns to the baseline. Wonder if its just my meter? Maybe effect of cosmic ray or alpha particle passing through either the meters voltage reference, or the external Vref under test ? I have also tested some other LM399 references and see the same effect.
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I have one of these Keithley 196 meters, from Ebay, which I have been using for recording the voltage of a LTZ1000 voltage reference. Of course, based on the specs the LTZ1k would be more stable than the meter. Anyway, I am logging data via GPIB and plotting the results. I see, for example, 7.23114 V with daily variations of about +/- 5 counts but every so often (maybe 1x or 2x per day) I get a single reading which is maybe 50 counts off the long term average, then it returns to the baseline. Wonder if its just my meter? Maybe effect of cosmic ray or alpha particle passing through either the meters voltage reference, or the external Vref under test ? I have also tested some other LM399 references and see the same effect.
Having started down the path of volt nutting with a handful of LM399's, I too have just ordered a Keithley 196 from eBay.
I'm curious, what did you use for your GPIB setup? Are you using a GPIB to USB adapter to a PC? If so, what does your script look like?
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Sorry for the delay, haven't been on the board for awhile... sadly my 196 has broken down. But I was using this USB-GPIB adaptor: http://galvant.ca/shop/gpibusb/ (http://galvant.ca/shop/gpibusb/)
actually he's now selling rev.4, what I have is rev.2 but I think it is similar.
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I love my 196! I think it will make you a very happy camper! (@cellularmitosis:I guess you're the one that got the 196 I had in my watch list on fleabay ;)
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Apart from certain MOSTEK EEPROMs (used in some HP and Tek products like the HP 3456A) that had manufacturing defects, EEPROMs generally seem to last a very long time. I'm sure there is a small chance for them to fail, but it's not like EEPROMs in instruments from the late eighties are failing in droves.
I believe those were MOSTEK mask ROMs and not any sort of PROM, EPROM, or EEPROM.
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To answer your question about code to read GPIB from a PC, I use Python to do that. I wrote about it here http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=3769&start=30#p47437 (http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=3769&start=30#p47437) but to save you the trouble, copied below. You would at a minimum need to change the serial port number to match whatever COM port the GPIB-USB adaptor ends up being on your system.
# Python 2.7 code to get readings from Keithley 196 multimeter via GPIB
# Assumes meter is already set up to correct mode, eg. from front panel
# Dec. 17 2012 J.Beale
from __future__ import print_function # to use print without newline
from serial import *
import time,datetime
cmd = "?\r" # GPIB command to Keithley 196 must end with carriage return
eol_str = "\n" # end of line string in file output
buffer ='' # serial input buffer
outbuf = '' # file output buffer
ser=Serial(17,460800,8,'N',1,timeout=1) # GPIB-USB board on COM18, with 460800 bps, 8-N-1
f = open('K196-log.csv', 'w')
print ("Keithley 196 log v0.1 Dec.17 2012 JPB")
f.write ("date_time,volts\n")
f.write ("# Keithley 196 log v0.1 Dec.17 2012 JPB\n")
while True:
ser.read(255) # clear out existing buffer & throw it away
ser.write(cmd) # send query to instrument
buf = ser.readline() # string terminated with '\n'
buffer = buf.split()[0] # get rid of the \r\n characters at the end
outbuf = str(datetime.datetime.now()) + ',' + buffer
print (outbuf)
f.write (outbuf)
f.write (eol_str)
time.sleep(9) # from 'time' to wait this many seconds
f.close # close log file
ser.close() # close serial port when done. If we ever are...
Example output:
date_time,volts
# Keithley 196 log v0.1 Dec.17 2012 JPB
2012-12-17 13:25:18.006000,+10.00400E+0
2012-12-17 13:25:28.115000,+10.00401E+0
2012-12-17 13:25:38.147000,+10.00400E+0
2012-12-17 13:25:48.225000,+10.00400E+0
2012-12-17 13:25:58.256000,+10.00400E+0
2012-12-17 13:26:08.365000,+10.00401E+0
2012-12-17 13:26:18.396000,+10.00400E+0
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The Keithley 196 analog board is almost 90-95% identical to the Tektronix DM5120, the 5120 has optocouplers vs the 196 has isolation transformers
The logic board is very different, simpler design in the Tektronix DM5120
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I've had a 196 for a while and like the meter but it needs to be warmed up more so than others I own. I wouldn't calibrate it until you warmed it up for several hours. Large, bright display. Mine seems pretty stable with repeatable accuracy over 4 months.
I also have a 195a and a 199. The 196 is clearly the better of all of them.
Jerry