Control Signal options

[Mikekc44]

I have a small pumping system that needs to be turned on or off by a plc base Scada system located in a different area of the plant. I also need to signal the main control system if my unit goes into a fault condition. I currently am thinking the best option is to use 24vdc control voltage for sending and receiving start stop or alarm signals. Using that option the main control panel would use a 24vdc relay and run two conductors from my panel to energize the relay if my system goes into a fault condition. When that relay energizes the main control system knows to shut down related pumping equp. Also we would have two conductors coming from the main control that would carry a 24vdc+ and 24vdc- currten to fire a relay in my panel to tell the unit to start or stop. Is there a better option that I could use. I am thanking you in advance for your input.

 

[rlundsrud]

Is the pump single phase or 3-phase and is it fed by a vfd? What kind of distance are we talking about from the PLC to the pump? Some more info on the pump controls would be helpful. I would recommend interrupting the pump control with a 24 volt relay and use a current transducer to monitor the status of the pump for your fault. If the pumps been enabled but no current is detected on the current transducer that would trigger a fault condition.

 

[Mikekc44]

The mixing skid im controlling consists of a small peristaltic pump 1ph 120vac only pulls about 2 amp, There is also a water solenoid valve in the unit only pulls about 1 amp. There are two flow sensors 24vdc powered that monitor flow. The distance from the main control panel and my panel is prob 200-300 feet at tje most. I suppose we could run a shielded cable with 6 conductors from the main panel to use 2 conductorsf for alarm condition and 2 for start stop and have a couple spare. I was just wondering if there was a better option.

 

[tom baker]

24 VDC is the best option as 120V circuits with relays don't work well over long distances, The coil will energize but may not drop out due to capacitive coupling. And then in your PLC cabinet you don't have a second foreign voltage @ 120v

 

[petersonra]

24 VDC is the best option as 120V circuits with relays don't work well over long distances, The coil will energize but may not drop out due to capacitive coupling. And then in your PLC cabinet you don't have a second foreign voltage @ 120v

at a couple hundred feet it is not going to make any real difference.