What are the differences between an electrometer, pico-ammeter and current amplifier?

Product(s):

Electrometer: 6514,6517A,617,614, 6512,602,600B

Pico-Ammeter: 6487,6485,486,487,485,480

Current Amplifier: 428-PROG, 428-MAN

Question: What are the differences between an electrometer, pico-ammeter and current amplifier?

Answer:

Pico-ammeters are similar to Electrometer design for current measurement.

However, Electrometers are multi-function (measure Resistance and Charge) and offer more sensitive ranges for the current measurement function. Greater sensitivity provides better resolution and improved accuracy for extremely low current measurements. Electrometers are a better solution for more accurate measurements in the pA range.

As usual, speed is a trade off for this accuracy advantage. The preamp settling time, defined as 10% of final value, on electrometer’s pA ranges is about 2.5 seconds. The preamp settling time on the nA ranges is similar to the picoammeter’s nA range, in the mS.

If fast acquisition is a critical application requirement, a current amplifier may be the preferred solution. Unlike the pico-ammeters and electrometers, the Model 428 offers selectable filters to accommodate for noise / speed tolerances. The 10 – 90% rise time can be configured as fast as 250uS on the 10 e 11 gain range with a 2pA rms noise level, or as slow as 300mS with 1.2fA rms noise level. Also different from the picoammeter and electrometer design, the current amplifier does not offer an internal A/D. The Model 428 has a 0-10volt analog output. This output can be used with data acquisition boards, oscilloscopes or waveform digitizers for low current measurement system or real time display.