Help in Wiring Interposing Relay

[TahirQ]

In a project,I am using an Output Card where I have been advised to use 24VDC interposing relays to give output signals to field elements. I have never used an interposing relay before.
Can somebody give me some information on what is the right method to wire an interposing relay with output card and Field elements (Actuators,Valves?. I have looked it up but have not found anything specific to my problem.

 

[ivo.maenen]

output1 -> 21 (NC-contact relay 2)
22 (NC-contact relay 2) --> A1 (relay 1)

output2 -> 21 (NC-contact relay 1)
22 (NC-contact relay 1) --> A1 (relay 2)

 

[Bering C Sparky]

Hello,
Attached is a crude drawing of relay coil fed from PLC Ouput, and field device wired through the relay contact.

I only used one contact in this drawing N/O but you should get the idea. (did this in a rush I just got off shift and want to get out of here before they want me to do something else tonight)

Did not know what voltage you are using but it will wire all the same just select the proper relays for the voltage you are bring from the plc and size them for the current your field device will draw.

With the relays in the circuit you can also power the relay coil with a Low voltage say 24volt from the PLC and use a higher voltage 220V for example through the relay contact to power the field devices if nessisary.
Good Luck
BCS

 

[Lancie1]

With the relays in the circuit you can also power the relay coil with a Low voltage say 24volt from the PLC.

Many PLCs have a built-in 24 VDC supply, but it may not be large enough to power external relay and solenoid devices. If there is an external 24 VDC power supply for the PLC, with a large-enough volt-amp rating, then it can be used for your external devices.

One of the first places to check is in the User Manual for your PLC. Many times there will be a circuit for using interposing relays.

An interposing relay is simply a in-between device that relays a small signal to switch a larger current.

 

[TahirQ]

output1 -> 21 (NC-contact relay 2)
22 (NC-contact relay 2) --> A1 (relay 1)

output2 -> 21 (NC-contact relay 1)
22 (NC-contact relay 1) --> A1 (relay 2)

Can you kindly explain this
with help of diagram?

 

[Bering C Sparky]

Can you kindly explain this
with help of diagram?

I have attached a drawing of what I interpret the poster said.
But honestly I am not sure what he is getting at this does nothing that I can see. (but I dont know everything so maybe he has a valid point and I just dont see it)
I would not even put this in your head, it will just confuse you.

Dont let the term Interposing relay get you confused.
Basically you just need to control the coil of a relay from the plc output (small current draw) and then control the load to the field device through the contacts of the relay. (the relay contacts are rated for a much higher current)

Things you must look out for are proper voltage of coils, relay contact current ratings, power supply having proper voltage and current capacity to your PLC and field devices.

BCS

 

[Bering C Sparky]

Forgot to attach the drawing.


good luck

 

[rdrast]

He's confusing interposing with interlocking.

 

[cnorm5623]

Here is a quick interposing relay diagram I found with a quick Google image search of "interposing relay wiring diagram"

where as CR AAA is a small relay controlled by the plc output and the contacts from that CR AAA relay control larger field devices.

I think this is what you were looking for.

 

[nwboson]

Just a quick reminder about sizing and protecting the interposing relay contacts:
1) If you are driving an AC load (actuator, valve, ...) , be sure to size the relay contacts for the AC inrush current of the device.
2) If you are driving a DC inductive load (solenoid, actuator, valve,...), the contacts on the interposing relay will see a potentially large negative voltage spike (depending on the inductance) when the contacts open. So put a diode (reverse polarity) across each contact to keep the contact from failing.