Safety Relay- Basic Question

Sundae8pm

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Join Date
Nov 2009
Location
Scotland
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6
This is my first time I have encountered a safety relay, and before I get flamed - it is not being used in a safety environment (bear with me...).

Due to an issue with test pulses, a relay is going to be put into a circuit to prevent test pulses from being detected as a true signal. A safety relay has been specified for me, on the basis that the dual contacts will reduce the risk of contact weld.

I have had a quick bench test of a Phoenix safety relay and I may have killed it. It appears that you cannot use external 24V as an input (there is a single input in the circuit, but a dual input is needed at the relay)?

The literature I have reviewed all show volt-free contacts at the stop functions and I can find nowhere that shows an external 24V input into a safety input. Has the role and design of the safety relay been misunderstood, or was my wiring incorrect (I managed to get a squeal and a spark from the relay) or was it a duff relay??

Essentially what I want to do is use a single PLC output (normally 24V, fail 0V) into a 'safety input'. Possible? (apologies for ramble...)
 
I used PSR-ESA4, but my question is not specific to this type (as my client has ordered the relays independently (edit) PNOZ S4...).
 
Yes you can. But you will have to select the right type of relay. Some relays are activated by power free contacts, and those relays can not be used in your application. Try to look at the MAS117T from AB. The output of the PLC powers this relay.
 
Thanks, is there a phrase or terminology to allow me to understand whether the relay specified accepts a 24V safety input (I fear the money has been spent on a wrong relay...)
 
Sorry, I gave you the wrong relay model (typing mistake).
MSR117T from AB or PNOZ X1 from Pilz.
 
Look for safety relays that can be used with light curtains and connect it configured for light curtains
 
Don't think there is a definite term to look for but if you see dual channel then that would be a no good. Have a look at this 515-1759 at rswww.com then download the data sheet, think that should do the job.

Bryan
 
You just have to look at the electrical connection before you buy the relay. Usually, a relay used for the Emergency pushbutton can be of the type I gave you the ref. If you want to use it to connect a safety door switch, you use your type. Your type can have one or two switch free contacts, depending on the safety level of the machine (2 or 3 or 4).
 
Ah, I may have made a schoolboy error.

I take it if I am using an external 24V as an input, then I don't need to connect the Power Supplies (indicated when connecting a light curtain)?

That might explain the spark I got...?
 
The model mentioned by Bryan, is of the same type I mentioned in my post. The 24VDC from the PLC output goes to A1 of the relay and A2 of the relay goes to 0VDC.
 
That was the easy way, but the load on the device may be too much (16 relays from a single PLC card) - 18W plus other circuits :( (and it isn't our PLC - double :(

Hence I went for external supply to A1/A2, then use S21/22 and S11/S12 as a dual input (as both need to denergise to allow an auto reset).

I have found a wiring circuit for a light curtain and it seems to indicate using A2 to ground, then external 24V to safety inputs (with no power supply). I will trial this tomorrow.

05lightcurtainj
 
Last edited:

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