Push Buttons, Sensors & Switches (etc)

[Vong]

Why would you need one, if you have a GuardLogix system? Can't you just wire two Prox Switches into a DeviceNET safety IO module and take care of the zero speed sensing with safety code? 

Having multiple prox flags on a shaft and using solid safety logic to identify machine motion should meet the redundant safety design of a cat 3 system, should it not? 

[Ozzy]

There isn't much of a point with a guard logix and analog safety i/o with prox probs provided the it's handled correctly and the line time/ cycle time is acceptable for the application.  These relays are for when a controller isn't available or as a cheaper solutions.  Same thing with the XM-220 in a Zero speed application (the Xm220 has reverse speed and over speed capability too a step up from just a zero speed relay) 

[Vong]

I agree, asuming the logic is sound (and it has to be, for that and everything else), then why not use the GLX? It's handling all the guard doors and estops anyway.

[Vong · Accepted solution]

Even though I futzed around with RS5k for an hour and made a sweet addon instruction that showed zero speed status, error outputs depending on type of fault (one or the other prox inputs going stale or mismatching) and an estimated RPM of the device, people with more experience than I were too worried about taking responsibility for coding a canned safety instruction. Which I understand, but I guess I'm more of a '**bleep** the torpedoes' type.

So we're buying zero speed relays. Though, not the AB relays, but the Honeywell FF-SR05932 which is CAT3! Fills a nice gap between the AB prox relay and MSR57P (which we're also using one of). We were planning on using two AB zero speed relays for a CAT3 rating, but the Honeywell can do it alone. 

http://www.honeywell-sensor.com.cn/prodinfo/safety_modules/datasheet/107052_11EN_1101.pdf