Hello Guys,
A couple of questions about analog inputs:
As I understand it, separate power supplies (separate from the PLC supply and Digital I/O) are sometimes used for analog sensors to reduce noise (contactors, relays and other switched devices can cause noise on +24V DC lines). Under these circumstances, do you use the separate power supply to power the analog module as well? Or just the sensors themselves?
Also, as I understand it, isolated analog modules have the common for the analog measurement circuit separate from the common for the module power supply. These, however, may need to be tied together if there is a risk of the analog common drifting too high with respect to the module common. Under what circumstances would you want the analog measurement circuit (sensor connected to + and - inputs) to be completely floating with respect to the module/PLC power supply?
Thanks!
A couple of questions about analog inputs:
As I understand it, separate power supplies (separate from the PLC supply and Digital I/O) are sometimes used for analog sensors to reduce noise (contactors, relays and other switched devices can cause noise on +24V DC lines). Under these circumstances, do you use the separate power supply to power the analog module as well? Or just the sensors themselves?
Also, as I understand it, isolated analog modules have the common for the analog measurement circuit separate from the common for the module power supply. These, however, may need to be tied together if there is a risk of the analog common drifting too high with respect to the module common. Under what circumstances would you want the analog measurement circuit (sensor connected to + and - inputs) to be completely floating with respect to the module/PLC power supply?
Thanks!