Safety PLC

Johnny Rotten

Member
Join Date
Dec 2004
Location
Ontario, Canada
Posts
194
Am going to be upgrading some of our equipment using a safety PLC, and sensors to Cat 3. I'm close to choosing the plc and what have people used with success for non contact sensors?

Thanks, John
 
Are you referring to single beam sensors?

If so, I've used Sick, Leuze, and Schmersal with success.

I tend to gravitate to Leuze as the pricing is good and almost always in stock.
 
The SafePLC is typically dictated by the platform you're using.

Sensors are tricky and I've never been fully satisfied with anything I used. Most safe inputs send out a stream of pulses and monitor for that stream coming back. This lets them check for circuit breaks, shorts, and wiring mistakes for E-Stops. I haven't found a no contact sensor that will pass these pulses through. There are some sensors made for particular safety systems that support pulses for their own system only, but they typically lack some key anti-tamper feature that still gets them stuck in Cat 3.

I did see one directional magnet based door switch that acted as a relay so it would pass the pulses, but I never got to see what brand it was or a part number. So, they exist, but are hard to find.
 
I'm referring to magnetic and radio frequency non-contact sensors.

I use the the Schmersal RFID based solenoid interlock and non-solenoid interlocks quite frequently. (RSS 36, AZM300, etc..)

I've found them more reliable than the coded magnet types (no wear, good range, easily daisy-chainable, etc..)

They are more expensive but I can also up-sell them. They are also category 4 / SIL 3.
 
Why go radio frequency vs coded magnetic sensors?

In my experience, coded magnet sensors can be flaky and give you a lot more false trips. The magnets have to be perfectly aligned and as guards and things wear out, you have machine vibration stopping the machine at random times, much to the annoyance of production.

RFID is a lot more forgiving with vibration, and you can typically move the actuator much further away from the sensor (but not so far as to actually endanger anyone) than you can with a coded magnet.
 

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