The functions required to measure low-level DC currents often far exceed what a digital multimeter (DMM) can provide. Generally speaking, the sensitivity of DMM is not enough to measure current below 100nA. Even at higher currents, the input voltage drop (voltage burden) of the DMM reaches hundreds of millivolts, so the current cannot be measured accurately. Electrometers can measure low currents very accurately, but the circuits and voltage, resistance, and charge measurement functions required to measure very low currents will greatly increase the cost of the electrometer. The Model 12 picoammeter combines the economics and ease of use of DMM with the microcurrent sensitivity close to an electrometer.
In low-impedance fast mode (FAST), the voltage drop at the input end is almost 0 (in the order of μV), and there is almost no voltage drop in the measurement circuit, that is, the internal resistance of the ammeter is almost 0, so it will not affect the original circuit In this mode, the measurement accuracy is higher, which is suitable for measuring objects with low voltage drop and high internal resistance.