Hello,
I asked this question on another forum, but didn't get answer. It seems there are here a lot of hardware people. I hope you'll help.
I need your advice about a problem of choosing appropriate relay that can influence a choice of appropriate SM output module. (I use S7 300 PLC)
I need to have a relay energized in normal operation. The relay is energized from SM output PLC module. This way, in case of power failure, PLC in STOP mode or wire brike, the relay will become de energized and thus ensure safe state of the plant. This relay is in a control circuit of a shut off valve on propan gas.
Now, possible problem is the fact that relay will remain energized for a long time (this can take months) and that is not good (may fail) but I have no other choice. A colleague advices me to use 24V DC relay since it is much more robust and unlikely to fail. On the other hand 230 VAC relays will fail faster if energized for a long time.
I don't know if this is the case. I need your help on this. I have two choices:
1. Use 24VDC DO card and 24 V DC relay for this "fail safe" application.
2. Use 230 VAC DO module and 230 VAC relay
What would you do?
I asked this question on another forum, but didn't get answer. It seems there are here a lot of hardware people. I hope you'll help.
I need your advice about a problem of choosing appropriate relay that can influence a choice of appropriate SM output module. (I use S7 300 PLC)
I need to have a relay energized in normal operation. The relay is energized from SM output PLC module. This way, in case of power failure, PLC in STOP mode or wire brike, the relay will become de energized and thus ensure safe state of the plant. This relay is in a control circuit of a shut off valve on propan gas.
Now, possible problem is the fact that relay will remain energized for a long time (this can take months) and that is not good (may fail) but I have no other choice. A colleague advices me to use 24V DC relay since it is much more robust and unlikely to fail. On the other hand 230 VAC relays will fail faster if energized for a long time.
I don't know if this is the case. I need your help on this. I have two choices:
1. Use 24VDC DO card and 24 V DC relay for this "fail safe" application.
2. Use 230 VAC DO module and 230 VAC relay
What would you do?