Eric Nelson
Lifetime Supporting Member + Moderator
EDIT: Sorry, guys. My post seems to have no word wrap. Phil, any clue why???...
For some reason, I'm second guessing myself, so I'm hoping you guys will straighten me out. As usual, I'll make it a long, boring story...
I have a stand-alone label applicator that is currently using an NPN sensor (Banner PicoDot PD45VN6C50Q) to register the label to a mark on round tubes. Tube spins on a mandrel, and when it sees a mark, it spits out a label.
The mandrels are on a indexing turret, which presents the tubes to the labeler. Since I only want the labeler to look for a registration mark when the tube is in position, I control it through the main machine's PLC. Sensor goes to PLC input, PLC output goes to labeler's input. Output mirrors the input whenever I allow it, using a PERMIT bit. Basically:
Sometimes we don't need registration, so I also had a bit to override the input via the HMI:
Of course, running the sensor through the PLC delays the response, but that has not been an issue until recently. We increased the rotation speed on the mandrel, and can no longer reliably detect the registration mark with the PLC. The input response time just isn't fast enough, plus scan time becomes an issue. The labeler has no problem reading the short duration of the signal, so my solution was to directly connect the registration sensor to the labeler, with a PLC controlled relay in series to enable/disable the sensor as needed.
For some reason, I'm second guessing myself, so I'm hoping you guys will straighten me out. As usual, I'll make it a long, boring story...
I have a stand-alone label applicator that is currently using an NPN sensor (Banner PicoDot PD45VN6C50Q) to register the label to a mark on round tubes. Tube spins on a mandrel, and when it sees a mark, it spits out a label.
The mandrels are on a indexing turret, which presents the tubes to the labeler. Since I only want the labeler to look for a registration mark when the tube is in position, I control it through the main machine's PLC. Sensor goes to PLC input, PLC output goes to labeler's input. Output mirrors the input whenever I allow it, using a PERMIT bit. Basically:
| INPUT PERMIT OUTPUT
|----] [-------] [----------( )
Sometimes we don't need registration, so I also had a bit to override the input via the HMI:
| INPUT PERMIT OUTPUT
|----] [---+---] [----------( )
| |
| NO_REG |
|----] [---+
Of course, running the sensor through the PLC delays the response, but that has not been an issue until recently. We increased the rotation speed on the mandrel, and can no longer reliably detect the registration mark with the PLC. The input response time just isn't fast enough, plus scan time becomes an issue. The labeler has no problem reading the short duration of the signal, so my solution was to directly connect the registration sensor to the labeler, with a PLC controlled relay in series to enable/disable the sensor as needed.
NPN Sensor Labeler
+---------+
| DC+ |-------------------------> 24VDC
| |
| |
| N |
| P DC- |-------------------------> 0VDC
| N |
| |
| | PERMIT
| OUT |---------------] [-------> INPUT
+---------+
Yes, I could have moved the sensor to a high-speed input on the PLC, used interrupts, used an SSR on the output, etc., etc., but the bottom line is that I don't use the registration sensor for anything in the PLC, so there is no need to tie it to the PLC.
Okay, FINALLY to my question (assuming anyone is still reading)...
This new setup works great, BUT there's no provision for running without registration. To run non-registered tubes, I have to bypass the sensor, allowing the PERMIT relay to give the registration signal. Can I simply install a selector switch across the sensor without damaging it? Like this:
NPN Sensor Labeler
+---------+
| DC+ |-------------------------> 24VDC
| |
| |
| N |
| P DC- |------------+------------> 0VDC
| N | BYPASS |
| | +--] [--+
| | | PERMIT
| OUT |----+----------] [-------> INPUT
+---------+
Or, do I need a second pole on the selector switch to also remove power to the sensor? Like this:
NPN Sensor Labeler
+---------+
| DC+ |-------------------------> 24VDC
| |
| |
| N | BYPASS
| P DC- |-------]/[--+------------> 0VDC
| N | |
| | +--] [--+
| | | PERMIT
| OUT |----+----------] [-------> INPUT
+---------+
Yes, it is a simple (and stupid) question, but it's bothering me...
-Eric
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