Keithley & TEGAM on measuring nanoamperes
I just got a nice note from John Tucker, lead marketing engineer –nanotechnology, research and education over at Keithley Instruments. His title shows what a cool company Keithley is. I mentioned them before when I gave a shout out to Keithley’s Low Level Measurement handbook in this blog. He has just read my latest article Measuring Nanoamperes, and John pointed out that the Keithley 2400 is not really an electrometer as I implied in the article. He writes:
I would like to complement you on your recently published article "Measuring Nanoamperes". I had the chance to read this on my flight down to Atlanta today. It was enjoyable reading.
I do want to point out that the model number referring to the Keithley Electrometer is incorrect. The 2400 is a SourceMeter and not an electrometer. The 2400 is as you mention more of a source-measure unit. I believe that the model that should have appeared for the electrometer should have been our Model 6157A. You might want to verify this with Paul Grohe. The 6517A is designed to measure femtoamps where the 2400 does not have that low of a current measurement range.
He is right of course— in my defense I want to point out that the 2400 SourceMeter is still a darn good instrument and my pals at the semiconductor companies like it since they can force a current as well as measure one.
I also got a nice note from Andy Brush, the CEO of TEGAM, a cool company in it’s own right, who points out:
Thanks for the article on sensitive measurements. One nit to pick: While the Keithley model 2400 can indeed resolve better than nanoamperes, it's poor (for Keithley) current measurement capability does not earn it the title of "Electrometer"… 2400 is a SourceMeter. The really interesting model (and the one Adam Daire wrote about in reference #7) is the Model 6430 preamplified electrometer. That unit can resolve attoamperes, and probably remains the top DC low-current instrument available.
Thanks to both these gents for pointing out that there are instruments beyond nanoamperes. Attoamperes. Wow.