×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Feed Back through series circuit

Feed Back through series circuit

Feed Back through series circuit

(OP)
I am using one series ciruit having no of switches connected in series through two wire cable.  I want to take feedback in control room, that which switch is operated, how it can be done? In this case I want use same pair of cable that is used for connection in series circuit.  

RE: Feed Back through series circuit

You can tell if one or more switches are open, by placing large resistors in parallel with each switch.  By judicious choice of resistance values, you can encode the switch information and measurement of the net resistance will tell how many switches are open.  This is how alarm switches are configured to distinguish between a normal switch open or a open circuit altogether.

TTFN



RE: Feed Back through series circuit

You could also use multiple diodes with the forward voltage drop.  Use numbers like 1, 2, 4, 8.....   The same procedure as with resistors.  Start with looking for the highest bumber and work back.  Is there an 8 in the number, is there a 4 in the number, is there a 2 in the number, etc.  An easy job for a PC or PLC.  Above four switches creates accuracy problems.

RE: Feed Back through series circuit

I agree, diodes are a good solution. But there's a catch. If you have long wires then you usually get 60 or 50 Hz stray voltage into your circuit. This gets rectified by the diodes and creates a hard-to-interpret mess.

There are (at least) two solutions; either use two diodes "anti-parallel" instead of a single diode or put a capacitor across the switch/diode part of the circuit. Select the capacitor to be around ten times the cable capacitance. A 100 m (330 ft) cable needs something like a 100 nF capacitor.

Gunnar Englund
www.gke.org

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources