I have another question related to the connection and operation of FP-RLY-422

Question

1. I use one 25 VDC power to supply power for all the five fieldpoint modules(i.e. V and C terminals of FP-2000, FP-AI-110, FP-AO-200 and FP-RLY-422 are connected) However, as cascading power from neighboring bases or network modules defeats isolation between cascaded modules. I want to know whether the switching of one channel of a module have influence on the reading or switching of other channels in other modules. May I need to provide seperate power supply for FP-2000, FP-AI-100, FP-AO-200, and FP-RLY-422. If FP-RLY-422 was suppled by power of 120 VAC. Is it OK. I read the manual of FP-RLY-422 which specifies 3 A at 35 VDC or 250 VAC. If I used it to control three heaters of 500 w each and
another 750 W. The current of each channel will be over 3 A. Can it be wired in this way?
2. I use FP-RLY-422 to control four heaters. Now I connected it in this way. I connect it firstly to one of four solid state relays for each channel of the fieldpoint relay. The solid state relay is just a open/close relay the input is 3-32VDC and the output is 110-220VAC/25 A or 240 VAC/50 A. In this case, I build the VI for the operation of heater just in two statuses i.e. on and off. In this case the temperature can't be controlled very accurately. I want to know whether I can build a VI based on PID control based on the present wiring of my cable (i.e. fieldpoint relay control on/off solid relay to control operation of heater indiretly). In this case may I wire the fieldpoint relay FP-RLY-422 directly to the heater of 750 W? I understand the fieldpoint relay FP-RLY-422 in this way. It is a mechanical relay and I can heard the sound when it switched between normally open and normally closed.
I think it have only two statuses i.e. on and off. In this case would you please explain how it contrl the output for the heater more accurately. Does it control by regulating the time being on/off?

Answer 1

Bo,
1a) All FieldPoint I/O modules are supplied operating power from the power supply in the network module. Certain modules may require additional power for sourcing power via outputs or inputs. Of the modules you list above, the following module requires external power; FP-AO-200. The following modules do not require external power wired to the V & C terminals; FP-AI-100, FP-AI-110, FP-TC-120, and FP-RLY-422. The V & C terminals are provided on modules that do not require them to simplify wiring (e.g. not requiring external terminal blocks if you have loop powered current transmitters).
1b) The FP-RLY-422 is rated for up to 3 amps at 35 VDC or 250 VAC. Currents above 3 Amps may damage the relays, the traces on the terminal base and FP-RLY-422 PWBs, and wi
ll cause overheating of the connectoer between the terminal base and the I/O module.
2a) You can use the FP-RLY-422 with a PID control algorithm to control the heater. However, as relays have limited life expectancies and are simply on/off the control will not be a fine as some other options. What may be better is to use a FP-PWM-520 pulse width module to control the solid state relays. You still control the solid state relay via on/off, but in this case, the on/off time can be occuring relatively quickly, and you change the amount of on time vs the amount of off time, to control the power going in to the heater.
Regards,
Aaron