MENTOR does test the overhead LIVE!
Not as stated. I know, because I designed one generation of the equipment used. It kept me busy for a couple of months. I suspect that it may have been replaced by now, as I did it around 1988, which would make it very old in terms of electronics. The previous generation was much bigger and heavier.
Anyway, it works, or worked in those days, by having an electronics box and a battery pack mounted to the pantograph base frame, which is carrying 25kV ac, plus huge spikes and transients. This energised and processed a number of strain gauge and LVDT sensors on the pantograph, such as left and right vertical load (the head being sprung lightly at both sides), and arm height. These were turned into FM signals in the audio band and propagated down what we jokinlgy called the worlds longest optocoupler, basically a 1 metre insulating tube, oil-filled, containing 2 fibre optics (the second one sent commands upwards to switch the unit on and off, or select calibration signals).
Inside the MENTOR coach a fairly ancient rack of Schlumberger equipment demodulated the 6 channels of FM telemetry, and some simple analogue computation derived wire lateral position from the ratio of left and right vertical loads, as well as any bumps and other irregularities, and the data ended up in a multichannel UV chart recorder.
Now I suspect it will all be done digitally. I wanted to at the time, but was only redesigning the upper set of equipment, that runs at 25kV, as they were, at that time, keeping the Schlumberger equipment, no doubt due to budgetary constraints. Now, of course, I would use at least 16 bit ADCs, and have a very much higher data rate, with a simple DSP processor at the live end just to multiplex the data, and soem kind of digital system in the operational area of the coach to do the main processing and recording.
MENTOR can be added into any loco-hauled train, subject to its speed restriction (from memory, 100mph), and there is no need to be powering down the system to use it. It does however have to go into a place where there is no overhead wiring, pantograph lowered first of course, to have the battery charged. If I was doing one now, I could make an isolated power supply that would withstand the upwards of 50kV spikes that are present, to eliminate the battery. Such is progress...
Oh, and by the way, the method of extracting lateral wire position (it is staggered within certain limits to spread pantograph wear) was developed by the British Rail Research Labs at Derby, a very innovative bunch of people, who used to look after MENTOR. British Rail were actually getting rather good at running trains before they were unnecessarily privatised, and some of their better assets, including the reasearchers, dispersed.
Biting the hand that feeds IT
