Why Safety Relay??

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Thread Starter

pandu

Hi all

I would like to know what is the purpose of Safety Relay?
I know we use it to connect EM.STOPs.

my questions is why we need this when PLC also has monitoring function of signals and can go to safe state when fail.

how the use Safety relay is justified??

Please share your expertise
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PANDU
 
S
Basically, without getting into particulars, it's used because the safety relay is designed to be a very reliable device, so it's used in places where the failure of a device could cause injury or death to people. (It can also be used to protect equipment when the risk/cost justifies it)
 
HI Steves,

but SAFETY PLC also providing the same functions and reliable.

Is there any particular feature that Stands out for using SAFETY RELAY even plant is operated by SAFETY PLC

or

SAFETY RELAY may not be required when already SAFETY PLC exists in the plant??

Rgds
PANDU
 
B

bob peterson

I think there is merit in using safety relays for simple circuits that are more or less self contained. It is usually more cost effective, and a lot simpler.

The more complex the safety system becomes, the more attractive a safety PLC becomes.

At around $100 for a simple system, it is very hard for a safety PLC to compete price wise with a safety relay.
 
R

Remco de Jong

Hi,

The use of a safety relevant relay is much cost-effective. A safety PLC is a much expensive solution.

Besides a very big or complex safety circuit makes it attractive to use a Safety relevant PLC.

If you only use it for EMG.Stops, Personally I choose a safety relay and a normal PLC where I make the feedback of that relay in my program.

If you're system must be in a Safety class 3 or higher and you must use of redundant signals, then maybe it's possible to use a safety PLC.

I hope this must help.

Best regards,

Remco de Jong
Electrical and Automation Engineer
Demag Cranes And Components
 
J
There are various types of answers to this question.

Perhaps the clearest is that the use of a Safety Relay is justified where it is required and is not justified if it is not required - typically systems are designed to comply with either codes or industry norms or sound and responsible judgement.

A safety relay is a relay which conforms to standards (where applicable) for safety related applications.

Safety relays also provide some features which aid it achieving require safety ratings (redundancy, self diagnostics, reliability ratings etc)
 
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