The safety functions (see below) in the Ammeter are implemented by combining different safety principles in order to achieve the highest safety level defined as SIL4 in EN 50129.
The measured current is detected when the current runs through a measuring resistor built into the Ammeter.
Two microprocessors (A and B) measure the voltage across the measuring resistor and send two independent A/B-telegrams to a serial line that can be read by a Railway control system e.g. an Interlocking system.
The telegrams contain time stamps, measured current, validity status and a CRC value.
Internally, the Ammeter continuously performs a self-test of the PCB.
The self-test is complete and advanced in the sense that it has a built-in fail-safe current reference and it is able to detect any single and multiple failures on the PCB-board e.g. after an over voltage event.
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