Electromechanical Totaliser

[sonu1978]

Hi
I need to check for an EMT(electromechnical totaliser) disconnection and EMT shorting using only two wires of the coil. How can I do it ??

One end of the EMT is connected to 24V DC and the other end is to a CPLD.

 

[VEBill]

Use a series resistor in the low leg to provide a 4.5 volt drop and then use a logic input to monitor this signal. This assumes that the counter will still work with slightly less voltage.

 

[OperaHouse]

If one side of the coil is connected to +24V you can sense the others side of the coil for voltage through a 47K resistor to th base of a transistor. Adding a diode and a 4.7uF capacitor can provide a hold in during pulsing. This will sense a missing counter or open coil.

Running a small current through the coil to make approximately 0.5 volt will allow you to sense an open or shorted coil with a high/low comparator.

Sensing coil kickback might also be a very quick cheap method of determining a functioning counter.