Schuetz Messtechnik GmbH

The MR300C-A micro-ohmmeter enables you to perform highly accurate resistance measurements at objects with an extremely low resistance such as cables, contacts, fuses, power connections, graphite, carbon and metal samples. In the lowest measuring range of 100 µΩ the resolution is 10 nΩ!

The MR300C-A micro-ohmmeter features a constant current system, which guarantees an extremely stable measuring current (max. 10A) during a measurement. The measuring result is calculated as the quotient of the voltage drop across an internal reference resistor and the (amplified) voltage drop across the test object. Before each main measurement, in which the measuring current flows, a zero measurement without measuring current is performed, in which any offset voltages, in particular the thermoelectric voltage, are determined at the test object. The zero point stored is compared with the actual value determined in the actual main measurement. After this, the result is displayed. Possibly a temperature conversion (see below) or other customer-specific conversions (e.g. linearization) are carried out before the result is displayed.

Due to this complex measuring procedure the measuring time of the MR300C-A is a little longer than that of comparable instruments. On the other hand, it is this complexity that guarantees the high accuracy and the very high long-term stability. The measuring current does not flow continuously, but only for a short period
of a measurement. For this reason, the heating-up of the instrument is reduced, and therefore a more compact design of the MR300C-A is possible.

Furthermore, the test object is Features measured more accurately, as it does not heat up. The temperature measurement converts the measuring value obtained to 20 °C using a coefficient of 0.392%/K for copper and 0.400%/K for aluminium. The object temperature is measured via a probe (option) or entered directly, the conversion can be switched off. Direct input of the temperature is the standard. As the MR300C-A performs a quotient measurement with exclusive reference to the internal reference resistances and compensates the offset voltages of the amplifiers and the thermoelectric voltage at the test object, an extreme stability of the measured values over long periods is reached. The measurement error reached only depends on the stability of the reference resistors. The modification and ageing of any components do not affect the result of the measurements in any way. Unlike reference voltages and currents, such long-term stable resistances can be realised easily.