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I have a M91-2-R1 to control 2 heatgun and 2 exair cooling vortex tube. I use 120Vac scr to start the heatgun and 120Vac solénoïde valve for the cooling. Do I need a RC supressor or other protection for the contact of the plc?

The cycle is

1. turn ON heater 7 sec. turn OFF heater and start cooling 7 sec. turn OFF cooling

2. turn ON heater 7 sec. turn OFF heater and start cooling 7 sec. turn OFF cooling

3. turn ON heater 30 sec. turn OFF heater

We make this cycle 7 hours per day.

Now I have a one bad contact relay.

The M91-2-R1 is the best to control scr and solenoide valve?

I chose this plc because I have a department that use 52 of this plc.


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  • MVP 2014

In terms of cycles, your process is 58 seconds long, and the heater cycles 3 times during that process. That equals approximately 1300 relay cycles per 7-hour day.

The relay contacts are rated at around 100,000 cycles. This would be reached in approximately 76 days in your application.

You should have RC suppressors, but even with those in place, based on the total number of cycles the relays would start failing sooner than you would like.

I would suggest using the M91-2-T1 and external relay modules, solid state relays if you can, and also use RC suppressors. In that configuration the M91-2-T1 should last "forever" and if you lose an external relay they are easy to replace.

On the other hand, since perhaps you have a lot of M91-2-R1 on site(?) maybe you can have a backup unit and swap it out when the relay fails. If you aren't planning to make a warranty claim for any other problems with the unit, an experienced technician can change the relays in the PLC quite easily. I only suggest going this way because you mentioned your other department that uses a large number of these.

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