New multimeter

[Guest]

Hi all,

You guys you appear to the font of all knowledge so I thoguht I'd ask here and get a good answer

I need a multimeter to measure uA and Idealy nA for my project, when I look at the description of handheld multimeters they say things like

DC Current range 400uA,4000uA,40mA,400ma,4A,40A

Does this mean that it will measure from 0uA to 400uA on it's lowest range? or only anything above 400uA?

Thx

[dyeatman]

Basically, yes to your first question and no to the second.

Each of the numbers in the list are ranges and are the the maximum for that range. For all the minimum is zero.

0-400uA
0-4000uA
0-40mA
0-400ma
0-4A
0-40A

The reason for the ranges is that, on the higher ranges, the resolution decreases for the low end.

[newguy]

If you have to measure on the order of nA, then a handheld multimeter just won't be very accurate. You have two options: you can invest in a bench-style DMM such as the Agilent 3458A Digital Multimeter (smallest range is 100 nA), or you can build a low noise amp. Not sure of the proper term for the amp (transconductance?), but it functions as a I-V converter. E.g. 100 nA in = 1 V out, or something like that.

That type of amp is easy to build. The only concern is really power supply noise, but if it's battery powered then it can be very accurate and reliable. Just be careful to properly calibrate it, and it will be MUCH cheaper than buying an accurate DMM/Ammeter.