Hey guys,
I had a question pop up the other day about the input leds on an AB AC input card. I almost never use AB but in the past I was thinking that on many PLCs the inputs are basically controlled by there own input power source...meaning the LED is on if the input device is passing power. I was sure that in some cases I have had a card pulled out of the rack with the input power on the LEDs would still be on if the device was on?? Or the CPU can be off and the input power be on and again the LED would be on... on many the input circuit shows normally an optic isolation between the input power and the card power... so my question was on the AB PLC if the power supply for the rack was off would the input LEDs remain off as well? I was thinking they would be on but I was proved wrong?? Am I remembering this wrong???
I had a question pop up the other day about the input leds on an AB AC input card. I almost never use AB but in the past I was thinking that on many PLCs the inputs are basically controlled by there own input power source...meaning the LED is on if the input device is passing power. I was sure that in some cases I have had a card pulled out of the rack with the input power on the LEDs would still be on if the device was on?? Or the CPU can be off and the input power be on and again the LED would be on... on many the input circuit shows normally an optic isolation between the input power and the card power... so my question was on the AB PLC if the power supply for the rack was off would the input LEDs remain off as well? I was thinking they would be on but I was proved wrong?? Am I remembering this wrong???