Mind the gap [electric trains]

Abstract

Engineers working on electric trains have struggled with the problem of ensuring that the pantographs keep as much contact with the overhead line as possible without damaging it in one of the harshest environments for electronics known. One system has stepped into the breach. Experience of electronics on trains dictates that both input circuit protection and galvanic isolation are essential (RIA 13 & EN50155). PanChex and the original pantograph telemetry developed by BR Research had used voltage to frequency and voltage to frequency conversion to enable digital transmission of analogue signals over a fibre optic cable. Although this method is useful for simple systems, it suffers from thermal drift. A small change in gain inherently creates a large change in output offset voltage. It was decided from the outset of this project that a standard analogue-to digital converter (ADC) preceded by a high performance instrumentation amplifier would be used to digitise the analogue signals from the sensors.