Doing a search on "linear position sensor" instead of encoder produces some promising results. I see some linear potentiometer type devices that are environmentally sealed and claim 10M cycle life. Don't know about the cost, or what 10M cycle life translates into in your application.
I see, and what ever we do will be better than the "Kentucky Windage" on the limit switches and the articulating strikers. I'd post pix but you would laugh! I'll post pix anyway!
Then that may be your answer. Read them with an analog input on the PLC and you can adjust your trip point to whatever position you want. Resolution based on the PLCs A/D bits and your scaling of the signal from the position sensor.
Bimba makes an air cylinder with a linear pot inside. We have been using it for about
200,000 cycles looking for a sealing washer. We feed the output it to an analog input of a plc. Washer is about 0.062" thick and their are some tolerance stacks so it has to working a reasonably tight degree of precision.
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On another line I see we are using a stick on tape and a mag scanner head to measure to
0.005 mm if I remember correctly, I'd have to look that up tomorrow in my files. I just ordered a meter of spare tape and a scanning head the other day. I think that head has RS422 output but I'd have to read the documentation. I really didn't care, I just wanted to order a spare to keep on hand. If I have spares it won't break.
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