Lavstrømsamperemeter

Lavstrømsamperemeter is an electronic instrument designed to measure very small electrical currents, typically in the microampere (µA) to milliampere (mA) range. It is used in electronics testing, sensor characterization, and leakage-current measurements where a conventional ammeter would introduce unacceptable loading or fail to resolve small signals.

Principle of operation: Two common approaches are shunt-based and transimpedance-based. In a shunt-based lavstrømsamperemeter, the current under test passes through a precision low-value resistor, generating a voltage proportional to current; this voltage is amplified and read by the meter. In very low currents, a high-sensitivity current-to-voltage converter, often using an operational amplifier with a high-value feedback resistor or a transimpedance stage, provides higher gain while maintaining low input bias. Instrumentation amplifiers and electrometers reduce input bias and noise to improve accuracy.

Key specifications include input range, burden voltage (the voltage drop across the measuring element), input impedance, accuracy, resolution, temperature drift, noise, and isolation. Low-burden design is essential to avoid altering the circuit under test, especially in high-impedance sources such as photodiodes or electromotive sensor outputs. Some lavstrømsamperemeters include galvanic isolation and guard shielding to minimize leakage currents and stray capacitances.

Typical applications cover characterizing photodiodes and sensors, measuring leakage currents in semiconductor devices, electrochemical cells, battery internal leakage, and hobbyist experiments where small currents are important. Some devices combine low-current measurement with other ranges, acting as a general-purpose meter with a dedicated microampere range.

Measurement considerations include temperature drift, input bias currents of the amplifier, leakage on printed circuit boards, humidity, and connector cleanliness, which can affect readings at microamps. Regular calibration against known standards improves reliability, and traceability is common in laboratory-grade lavstrømsamperemeters.