Detect Signal Failures on the Rail - Scanning Audio Frequency Rail Current Detectors

After an exploratory meeting with a Superintendent of Signals at New Jersey Transit, we were shown the "homegrown" explorer coil they used to troubleshoot signal issues on the rail.  The unit worked well but was very limited in frequencies and heavy and cumbersome to use.  At that point we developed the first of our Rail Current Detector line, the Multi-frequency Rail Current Detector. The device covered the 4 mainline track frequencies they used from 60 to 250 Hz and was very easy to use, able to be rolled on the rail by the signal maintenance person. The device had a high quality meter with LED illumination, audible output, LCD frequency and battery display, frequency selector and gain control. Several agencies around the country (See below) have these units still in use everyday.

Other agencies showed interest in our Rail Current Detectors but wanted to be able to detect many more frequencies, especially those in the Audio range.  We determined that it might be very advantageous to give the new Audio frequency units the ability to scan the range of frequencies automatically upon startup to see what the rail under test might show.  Once the unit found the frequencies they were looking for, they could just select the frequency to test and proceed down the track looking for ground faults, shunts, partial shunts etc. We later determined that the ability to troubleshoot at frequency would lend our unit to testing of insulated joints (IJs), impedance bonds and insulation on switch components.  These units are hard at work at SEPTA, LA Metro, MBTA, WMATA, MARTA, MTA Maryland, New Jersey Transit, ConRail, Port Authorities of NY/NJ and Allegheny County, PA and many others.

After multiple meetings and demos of our Rail Current Detectors with the NYCT Subway Signal Maintenance Department, it was determined that a simpler and more ruggedized device needed to be designed for their use.  Their old units, nicknamed "hounds", were not frequency selectable and had a design that was not the most robust when used in the field.  The New York subway system uses only two frequencies, 60 and 25 Hertz, with 60 being the most widespread.  Since it was not always clear which frequency was present in a given track crcuit or section, our analog design engineer gave it the ability to find the highest current of the two frequencies and lock it in for easy detection.  

The old hound units they had employed a red LED bar graph display which they liked, but we determined that the Tri-Color display of green, yellow and red gave more information about the relative loss of current.  The audible transducer output begins beeping at the point where the display goes into the red section of the bar graph.  The power-on switch has an LED illuminated ring which will flash fast at 60 Hz and slow at 25 Hz to let the user know which frequency is on the track circuit under test.  Also, it will double flash quickly when the batteries are low.  The unit has a ruggedized guard around the top edge of the console and the display has a sun shield/guard for day light viewing and protection of the display.  Like our other units, the device can work for about 40 hours on 3 regular AA alkaline batteries in a sealed battery holder in the handle.  New York City Subway has purchased 70 units to date and they have plans to purchase many additional units.