I am trying to install a laser micrometer. it measures the diameter of a wire as the wire passes through it, and records if/when the wire goes out of tolerance (too large/too small). The micrometer needs a footage pulse input for this. This is usually accomplished by installing a rotary reed switch between terminals 8 & 9. The reed switch will pull the 5V terminal 8 LOW (draws 10mA when closed) and the laser micrometer registers this as a pulse. There is no reed switch currently in place and I am trying to avoid adding one by using an already in-place 12V encoder signal. The encoder signal currently goes to a footage counter mouned right next to the micrometer so logistically it's easier. I can't figure out how to do it. I tried using a transistor but it didn't work. please have a look:

The thing in the top right is an exploded view of the encoder, which is shown in the top left terminated at the existing counter. White & green correspond to Data A & B. Black & red correspond to +VDC & common. Black lines correspond to what's already in place, and blue lines correspond to my addition.

transistor is 2N3416

 

Optoisolators on both if they can source enough current.

 

Optoisolators on both if they can source enough current.

I just rummaged through all the crap I have here and my only opto is a MOC3021 Triac.

I just tried basically the same thing as my original plan with the transistor, only this time with a IRFD113 mosfet and no voltage divider, and that didn't work either; I was sure it would.

 

Are you looking for the low-high transition on Data B or vice-versa?

What are the logic/input settings for input B config switches on the PLC?

Do you have a means of checking the voltage levels - say with a CRO...?

Also any limitations / requirements for the minimum on-time duration at the laser micrometer control? What's the encoder output pulse width?

 

Are you looking for the low-high transition on Data B or vice-versa?

either rising edge or falling edge, doesn't really matter. signal can be inverted.

What are the logic/input settings for input B config switches on the PLC?

The dip switches are factory default, just the way they're shown in the graphic.

Do you have a means of checking the voltage levels - say with a CRO...?

yes, I have a fluke scopemeter and a multimeter

Also any limitations / requirements for the minimum on-time duration at the laser micrometer control?

That remains to be seen. Everywhere I have seen these laser micrometers set up, the rotary reed switches give them 1 pulse per foot. If I can get the encoder input to work, it will be recieving 100 pulses per foot. The laser mic has a feature to scale the pulses, but I'm not sure what its limitations are.

What's the encoder output pulse width?

Well, I guess the pulse width would depend on the speed. its just a square wave.

BTW to save you some time, if you are going to come up with a big circuit, I wouldn't. I plan to get an optoisolator tomorrow (unless you see a reason why that wouldn't work) - but I was just trying to make sure there wasn't an obvious immediate solution that I was somehow overlooking.

Thanks