E-stop safety circuits

[tee-eff-ten]

I need to modify some machinery stop circuits but I don't want to do anything that would be detrimental to the standard requirements. Does anyone know where I can find the definitions of the Catagory 2, 3 etc that the standards quote. More specifically would it be allowed to daisy chain many NC E-stops to a bog standard relay and wire that to the Safety Relay as opposed to the contacts directly to it as at present? This would help me in building a monitoring systen for each E-stop without interfering with the operation of the Safety Relay. Thoughts welcome...

 

[montybaber]

Try Pilz GmbH & Co. KG

most of the standards etc are covered

 

[xraytek]

More specifically would it be allowed to daisy chain many NC E-stops to a bog standard relay and wire that to the Safety Relay as opposed to the contacts directly to it as at present?

No because a standard relay has the risk of failing to operate.

You say you want to add monitoring to the e-stops. Do you want to know which specific e-stop has been activated, or just a single alarm when any e-stop is hit?

Can you provide more details of the type of equipment and exactly what you want from this safety circuit?

 

[silva.foxx]

Take a peek at this...think it over...

Safety Circuit - control system design, failsafe relay.

although we're probably bound by Cat 3 and 4 safety circuits...it's quite a thought provoking "opinion".

Google Pilz, Schmersal, Guardmaster, safety relay, blah blah blah

 

[tee-eff-ten]

To answer xraytek's question, yes I want to know which stop is activated. Take this specific example: I have a DOLD Safemaster relay with 8 NC guard switches series wired in the S11 -S12 monitored stop circuit. In the past an LED has been used as an indicator accross each switch contact to indicate which switch is open, however this is a little hit and miss (and probably not officially recommended) because on occasion the 10mA current through the LED is enough to upset the Safemaster. It is not that the unit does not drop out, but sometimes it will not reset properly. What is the normal approach to the problem of a visual indication of which guard is open?

 

[silva.foxx]

What is the normal approach to the problem of a visual indication of which guard is open?

Use 3 pole safety switches (or e/stops) ie. 2 n/c to the SR and 1 n/o for indication purposes.

.

 

[tee-eff-ten]

I was waiting for that one silva.foxx! The switches are already 2 x NC as they signal to the main plc that controls the machine. Unfortunately I waste many hours tracing faults whereby the switch ( limit switches or key interlocks) is stuck between open & closed, giving an ok signal to the plc, but no circuit on the e-stop, or indeed the other way round! I need a way to monitor the ACTUAL e-stop contact. Hope this clarifies.

 

[xraytek]

Are there many e-stops?
One option is wire each e-stop into its own local safety relay, then loop your DOLD Safemaster relay through each relay.
A spare set of contacts on each new relay could then be used for monitoring.

 

[tee-eff-ten]

Yes there are many e-stops. To give you some idea I have manufacturing machines 23 m long that have 8 to 12 guard switches per relay, and up to 10 relays per machine. We have 15 machines. A more cost effective method is preferred!