0
\$\begingroup\$

I am wondering on how the industrial section deal with situations where a button is several meters away from the controller.

enter image description here

Is there a device that specifically handle the debouncing/filtering/protection for the controller? I doubt that the PLC handle this by itself. What would it be called?

\$\endgroup\$
3
  • 2
    \$\begingroup\$ Doesn't the PLC have protected inputs? Then you debounce in software. \$\endgroup\$
    – DKNguyen
    Commented Oct 7, 2020 at 15:14
  • \$\begingroup\$ Why do you doubt that it's built into the PLC? I thought that was the appeal of PLCs - that you can just connect them to stuff. \$\endgroup\$
    – Criticizing Israel not allowed
    Commented Oct 7, 2020 at 15:20
  • \$\begingroup\$ Of course the PLC does all that. Mostly already in the I/O Cards \$\endgroup\$
    – schnedan
    Commented Oct 7, 2020 at 15:20

1 Answer 1

Reset to default
1
\$\begingroup\$

There's usually no problem.

  • PLC inputs typically take 5 to 10 mA (check the manual) on 24 V inputs. This is enough that EM interference is not a problem.
  • I'd say that 50 m would not be unusual for a button or sensor.
  • The PLC inputs are scanned every few milliseconds. This by itself provides some debounce filtering along with whatever filtering has been designed into the electronics of the input circuitry. Again the manual should have some information on this.
  • If you're paranoid and need to debounce in software it's as simple as a time delay on the input.

Pseudo-ladder logic.

   Input              +TON-------+
---| |----------------| 100 ms   |
                      +----------+
   TON.DN
---| |-------- whatever
\$\endgroup\$
2
  • \$\begingroup\$ Thank you for that answer, I am doing this for my room and the switch is definitely very far from the controller. I considered buying only the I/O module just for the reliability that i know they wont break from interference but it seems it very difficult to interface them with a microcontroller and buying a plc is just too expensive for the project. I have modified an old circuit that already even has hardware debounce. The circuit is digitally isolated so i know that my microcontroller will be safe,as to this part of the circuit i dont know. what do you think ? \$\endgroup\$
    – DrakeJest
    Commented Oct 7, 2020 at 19:54
  • \$\begingroup\$ This is rather a different question to that at the top of the page. I can't try and resolve this in the comments. \$\endgroup\$
    – Transistor
    Commented Oct 7, 2020 at 22:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.