I have both the Keithley 155 and several Fluke 845AB's. I too prefer the Keithley 155 over the Fluke and I'm not a big fan of Keithley equipment. Jeff - KDØORH
----- Original Message ----- From: "R.Phillips" <[email protected]> To: [email protected] Sent: Wednesday, February 11, 2015 6:00:42 AM Subject: Re: [volt-nuts] Calibration of voltage standards I think I was the Keithley 155 owner that ask the question. Since then I have added an HP3245A to my equipment which I have set to 1.000000 V DC, read by my "in calibration" HP3458A, and then compared by the Keithley 155 against my Fluke 732A's 1.000 v output - this is showing a steady -1 uV on the 155's , 1 or 3uV range. I have replaced the batteries in the 155 with 9 volt (6LF22/MB1604) batteries, works fine. I also have a Fluke 845AB which I would suggest is less stable. Best regards Roy Phillips. -----Original Message----- From: [email protected] Sent: Wednesday, February 11, 2015 10:00 AM To: [email protected] Subject: Re: [volt-nuts] Calibration of voltage standards for those interested, and for simplicity, wanted to add this from David which was in voltnuts in 2012. ________________________________ From: Charles P. Steinmetz <charles_steinmetz at lavabit.com> To: Discussion of precise voltage measurement <volt-nuts at febo.com> Sent: Saturday, 15 December 2012, 10:28 Subject: Re: [volt-nuts] Fluke 335A versus HP 740B David wrote: > I have a Keithley 155 Null Detector how does that rate? The three usual suspects are the Fluke 845AB, the HP 419A, and Keithley 155. I have one of each, and they are all good meters. The received wisdom is that the Fluke is the one to have. However, in my view, the Keithley is the best of the bunch. It is a bonus if you find one with the rare 1554 AC power module (the 1554 mounts to the rear panel and allows AC operation -- otherwise, it is battery-only). The main problem today with the HP is that it uses impossible-to-find batteries. Not only are the original batteries unobtainable, I have yet to find a satisfactory replacement strategy. It also does not have a +/- 1 uV range, although I do not count that as a major fault since thermocouple noise in the measurement setup frequently prevents taking full advantage of the 1 uV range. The Fluke's batteries (sub-C NiCd cells) are readily replaced (though not inexpensively, if you get the best cells). Keithley used four, # 246 9 V carbon cells, which can easily be replaced with common 9 V alkalines or 9 V primary lithium cells that simply plug into the existing connectors. The HP and Fluke both use photocell choppers. Fluke published pre-release information indicating that they had designed a FET chopper for later production, but I have never seen an 845 with a FET chopper or a schematic of the FET chopper. (Does anyone here have either?) The Keithley was designed with a MOSFET chopper from the start. Not only is the Keithley the most modern design and the most likely to remain reliable, it also performs the best in my lab. I have had fewer ground loop and shielding problems with it than with the Fluke, and it has less noise and less drift. It is not enough better that most people should sell their Fluke to get a Keithley just for the performance difference (reliability may be another story), but -- IME -- it does perform better. They are all good meters, but IMO the Keithley is the best of the three. If I had only one, that is the one I'd want. Best regards, Charles _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
