Over the years, test and measurement companies have sought for a feature in relays that provides an accurate reading at low current. This is important because at very low current, there is a tendency for inaccurate measurements to occur, thus causing false readings. This feature is referred to as Thermal Electromotive Force (EMF), and is found in a few Relays.
Thermal Electromotive Force (EMF) is generated when the dissimilar metals that make up terminals, contact springs, and contacts touch. This electromotive force, measured in micro volts, could be very small or large, and can create undesirable noise during electrical measurements.
Low ampere switching is used for test and instrumentation measurements so there is a greater tendency for stray voltages to introduce errors into the signal path during measurement. The need for a low thermal EMF is desirable because it reduces thermocoupling (a junction between two different metals that produces a voltage related to a temperature difference) and provides a true voltage measurement at very low signal levels. When the EMF is small, the generated noise allows users to obtain the most accurate values while taking their measurements.
Panasonic offers a variety of Signal Relays with low EMF for the test and measurement industry, such as the TX-S, TX and TX-D Series.