Use of relays for Sensor outputs

[kulgauravkanade]

Hey Fellas,

I am trying to wire up 4 different sensor outputs to a VSD to issue a stop signal on detection of an obstruction. The application is a turntable and the sensors are proxy sensors with 4 meter range, so the idea is to stop the Turntable on detection of an obstruction on any one of the four sensors. I am using the Run enable function on the DI of the VSD (VACON 20) and cant use four different DI's for the four outputs of the senors.
My question is to how to wire up these outputs so that I can use a single ID on the VSD. (I've suggested using SPDT relays in series) Would that work?

Thank you.

 

[James Mcquade]

If the signal to make the system has power "1" then you can wire the 4 relays in series using a n.c. contact. when a proxy turns on, the coil energizes and the contact will open and thus remove the run signal.

hope this helps.
james

 

[kulgauravkanade]

Hi James,

Thank you for your reply mate!

The signal from the sensors are N.C (since I am using the Run enable command on the VFD. The signal turns off on detection on an obstruction and thus stopping the VFD, disabling the Run enable).
So should I be using the N.O contact on the relays whilst connecting them in series (so it is closed when there is no obstruction and opens on detecting an obstruction).
Please tell me if I am missing something.

 

[OkiePC]

I believe you have it right. WIth no obstruction, the sensors will hold the relays in an energized state and their contacts will be closed. If a sensor circuit opens for any reason, the relay will "drop out", its contact will open and the series circuit will open to the VFD.

The way you have it will also issue a stop command if a relay fails or a wire breaks which is often the best outcome.

 

[kulgauravkanade]

Yes, I hope it works!

Each of the four sensors driving a relay,
24 V DC connected to all the first trigger the NO of the first connected to the second trigger the NO of the second connected to the third trigger and so on..
with the final output connected to the VFD.

Sensor 1 2 3 4 driving separate relay coils with the other end of the coil grounded.

Thus, if sensor 1 detects an obstruction the coil de-energizes, returning the contact to NC, thus breaking the series connections (24 V DC to trigger - NO to trigger - NO to trigger -NO to digital input to VFD)

I hope it works!
-_-



Such an amazing community at PLC talk! Respect!

 

[Jeev]

Depending on your sensors, you might want to consider putting a time-on/time-off delay timer relay in your system. You don't want any nuisance switching to cause issues with your drive. For example, if you are using photoeyes and they are finding gaps in the objects, you effectively get pulses on your "Run" signal.