Sensors that won’t quit – one Balluff customer’s experience

We often hear companies talk about how great their products are or how well they hold up under adverse conditions, but many of us wonder just how much of that is hype.  While I cannot vouch for all the claims out there, I can relate to you (the reader) and share my Balluff prox story and how I’ve seen them survive.

I was working in the industrial maintenance field when I came across the prox in this tale.  The prox was being used to sense motion of sanding tape in a polishing machine.  This system was designed to polish the part in two directions and the purpose of the prox was to ensure that a proper amount of sandpaper had advanced with each direction change. The sandpaper was on rolls, which threaded through some rollers, including a plastic one that had a piece of metal embedded inside.  The prox was set up to monitor this plastic roller and register when the metal piece rotated by and thereby indicating to the system that the sandpaper had advanced.  If this prox did not change states, the system would fault out and turn on an error/alarm light.  To reset the alarm the operator had to hit a reset button and then start the system again.

On the day in question, I was called over to one of the polishers because the operator was having trouble with the system faulting out intermittently.  As improperly routed/installed tape rolls were a common problem with this operation, I generally started there when troubleshooting the system.  This time I found that not only had the operator routed the tape wrong, they had placed it in such a way that the abrasive side of the sanding tape was running across the Balluff prox that was used to ensure tape advancement.  The entire front of the prox had been sanded down to something between a 30° to 45° angle, with very little of the flat tip remaining.  At best there was maybe a sixteenth of an inch of the flat end surface left.  Now here is the amazing part, the prox was still functional!!!  The operator was only having an intermittent problem with the machine, which means the prox was still functioning most of the time.  In fact I verified this by advancing some of the tape by hand and watching the indicator light change state on the prox.

Of course I knew that this was the problem with the system, given the damage to the prox, and thus began to remove the prox from the system.  This is where I got my second surprise of the day.  I had changed many of these prox switches and it was not uncommon to do so under powered conditions as most of the ones we used had handy screw in connectors that made replacement a breeze.  Now the proper manner is to unscrew the connector, then remove the prox from whatever bracketing is used.  I was not thinking and started by removing the prox from the bracket first.  It was at this point I discovered that not only was a large chunk of the tip of the prox gone, but the live wires inside were exposed.  Yes, I discovered this in the way no maintenance person should… by being shocked.  Luckily for me it was a low voltage prox and the shock was very minimal.  And while this is an entertaining portion of my story, it also demonstrates how damaged a Balluff prox can be and still function at least intermittently.  At this point I stopped removing the prox from the bracket and removed the connector and thus power.  The rest of the story is much more boring and fairly standard as far as replacing a prox goes.

I would like to close with a few of my observations.  Balluff prox switches live up to their hype.  I have seen them put in horrible conditions and greatly abused, yet continue to work.  Balluff equipment was used in the facility in the story long before I worked in their maintenance department and I feel safe in saying they are still widely used there today.  There is a reason why they are widely used and I think my story illustrates that.  And, in case any of the readers of this are wondering, I am not receiving any compensation or the like for my story; I am simply sharing what I have seen.  I know I value the experiences of others and I hope that my story is interesting if not outright valuable to you, the reader.

Safety Disclaimers:  Balluff prox switches may still function when the internal electrical components are exposed so always kill or disconnect the power before removal.  Also remember amperage of only .05 Amps can be fatal so always, always, be cautious with electricity.