Track circuit equipment test bench

The bench is designed for testing, adjusting and post-repair acceptance of audio-frequency and coded track circuit equipment: track transmitters, track receivers, filters, track transformers and impedance bonds, as well as complete trackside junction boxes. In the signalling workshop it reproduces the electrical conditions of a rail line and allows the parameters of every unit to be measured before installation on the open line or at a station.

The instrument rack houses a test signal generator with the carrier and modulation frequencies of audio-frequency track circuits, a source of power-frequency code signals, an adjustable load and a rail line simulator — a set of equivalent circuits with adjustable length and ballast insulation resistance. The unit under test is connected to the patch field through plug-in connectors, after which the operator sets the mode and reads the input and output voltages, current draw, frequency and transfer ratio. The pick-up threshold of a track receiver is found by lowering the signal level smoothly until its output relay drops away.

Measurements are taken by the built-in multichannel voltmeter and frequency meter; the results are shown on the bench panel and passed to a computer for the test report. On request the bench is supplied with additional rail line equivalents for other track circuit types, an impedance bond test module measuring transformation ratio and insulation resistance, a set of cables and adapters for the workshop's apparatus, and an oscilloscope for checking signal waveforms.