EM Electronics N1a Nanovoltmeter
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The N1a from EM Electronics is one of the few low-noise nanovoltmeters around. I use the N1a for comparing voltage sources, for instance, when a better resolution and lower noise is required than can be provided by the Keithley 181. The N1a does not feature a digital interface, so I have to add a multimeter to the analog output of the N1a if I have to acquire data.
The N1a is based on the traditional chopper principle, but with the important enhancement in form of a transformer which couples the chopped signal to the first amplifier stage. This can be used to lower the equivalent noise from the amplifier drastically. EM specifies the input noise of the N1a to equal that of a 60 Ohm resistor. To get lower you will have to take a look at some of their more recent models, such as the P13a with an input noise equivalent to a 0.25 Ohm resistor. I salvaged the N1a from a metrology laboratory which was about to toss it out due to a combination of instrument malfunction and a declining need for this kind of instrument. With a slight effort I managed to bring it back to a working condition. See more on the repair pages. The instrument may appear slightly old-school, but it's actually very cool. |