The MRC 100S-BD-3 Bounding Tester is a battery-powered portable digital ohmmeter, which can be used, for example, for testing the ground connection in any section of an aircraft using different measuring currents (up to 10A). This high current ensures that any uncertain connections are recognised.

In addition to that a special firmware ensures that uncertain connections, which are in most cases characterised by unstable measured values, can be detected easily. An unstable value is indicated like a normal measured value, however, the “Error” LED at the front panel is ON. In most cases a whole series of measured values are recorded. The MRC100S-BD stores the last 100 measured values, even when it is turned off, so that the values can be transferred to a higher-level computer later via the RS232C interface. The measuring time, i.e. the time the current flows, can be pre-set in a range between 1 sec. an 60 sec. With a measuring current of 10 A test objects of up to 1000 mΩ can still be measured depending on the feed line resistances.

The higher the feed line resistance, the lower the limit. To be able to measure 500 mΩ properly, these resistances must not exceed 2×250 mΩ, including the contact resistances. In case the voltage drop across the test object and the feed lines exceeds 10 V, a current error is signalled, since the current cannot reach the 10 A level.

Nevertheless, the measurement is correct, as, due to the quotient method used, the measuring current always flows through the internal reference resistance, too, and the two voltage drops Ux/Uref can be offset. Measured values obtained in this way are marked by “*.

In case the current is below 70 %, the Features measurements are stopped and a general error message is displayed. In case the measuring time is more than 3 sec., the measured value is constantly updated at a rate of two measurements per second. The built-in battery unit is of a module design and can be replaced easily. Since the number of measurements is limited in the case of long measuring times and high currents, a second battery unit can be charged in the meantime. The battery unit in use can be charged using the built-in battery charger; this is normally done overnight, as the charging takes several hours. With the battery charger for the external battery unit, the charging time is reduced to 2 hours.