I am building a backup generator controlling it with a Click plc. I need to monitor if the motor is running. I have a coilx circuit (used to clean up pulses for a tachometer) that takes the high voltage ignition pulse and converts it to a 5v clean square wave. My click plc input needs an on voltage of 19v to 24v with a minimum current of 3.5ma to a maximum off current of .5ma. I saw this schematic posted over a year ago by ScottWang (see attached) and wonder if it would work by changing the voltage to 24VDC. I am doing the high-speed input calculations in the plc to know when the motor is up to run rpms I'm thinking 200 RPMs so about 3.5Hz. Any help or input would be greatly appreciated.

 

Should work.

"a maximum off current of .5ma. " is not clear. Do you have more information about the PLC input? R5 might not be small enough if sinking current is required. A partial schematic would be best, but a datasheet would help.

ak