arkyny
Member
No, Little Rock, Ar home of the losing hogs !!
Maybe if I ask specific questions I could grasp this ?
Does the PLC run the same voltage from inputs to outputs on every device?
Is the PLC capable of energizing the output device directly or through a control relay?
Whatever you want it to be. It could be 24VDC, 110VAC, or any other Voltage compatible with the Device and Input Card, even an Analog Voltage.I'll rephrase my question: I want to turn on a two pole contactor with a 110 volt coil. 110 volts is the control voltage to do this.
How is the PLC wired to make this happen?
The input voltage is what?
The output voltage will be the same?
Is there just one control voltage used for the entire PLC ? Eg. 24vdc. And all the outputs are 24vdc coil relays and the 110 volt lighting circuit runs through a set of dry contacts to the lighting contactor?
In addition, this where (sinking) NPN and (sourcing)PNP is determined ..yes?
So, you have an input card for each specific voltage you need to control eg. 110 volts, 24vac, 208 volts etc...
then through PLC logic, the program, when all the parameters, bit boxes, are true... PLC sends a signal to an output card that energizes a device.
This is why the PLC doesn't care what the voltage is that its controlling...Just needs to choose the correct Input and Output cards. The PLC interfaces the input/output cards. Is my thinking correct ?
In addition, this where (sinking) NPN and (sourcing)PNP is determined ..yes?
I do understand about only specific voltage can only be used on a device or equipment requiring that voltage.
I am understanding this is logic rather than physical, pertaining to the PLC.
I'll rephrase my question: I want to turn on a two pole contactor with a 110 volt coil. 110 volts is the control voltage to do this.
How is the PLC wired to make this happen?
The input voltage is what?
The output voltage will be the same?
So, I would wire 110 volts to a terminal on the PLC, when all of the bit boxes are true the output terminal for that circuit will energize the lighting two pole contactor's coil.
Another device may have 24 vac control circuit. I would use the same procedure.
And so...
OR...
Is there just one control voltage used for the entire PLC ? Eg. 24vdc. And all the outputs are 24vdc coil relays and the 110 volt lighting circuit runs through a set of dry contacts to the lighting contactor?
Hmmm...HVAC is one of the most difficult areas to use PLCs. The reason is that many HVAC systems use 24 VAC as the control voltage. That is a very rare voltage to find in PLC input modules. Many PLC inputs will accept a range of DC voltages and some accept 120 or 240 volts AC, but not low-voltage AC.In my field, HVAC, these will definitely become more preferred.