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!

*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.


HELP! complex pulse using ladder logic & timers

HELP! complex pulse using ladder logic & timers

I'm trying to create a repeating "complex pulse" using ladder logic timers in an TECO SG2.

I've tried the ladder logic below using an TECO SG2, but pulse output looks nothing like desired.

Any one have a different approach? THX in advance.

PULSE (all times in ms)

----| |----------------------------------------------O-- (input to start an Off-delay timer for total duration = number of pulse repetitions)

----| |----------------------------------------------O-- (flash timer 600ms on then 400ms off)

----| |----------------------------------------------O-- (flash timer 50ms on then 100ms off)

----|/|----------------------------------------------O-- (flash timer 300ms on then 100ms off)

----| |----------------------------------------------O-- (output relay combined from flash timers)
----| |---------------| |--------------------|

RE: HELP! complex pulse using ladder logic & timers

Is this for school?

"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Forum Policies for tips on how to make the best use of Eng-Tips.

RE: HELP! complex pulse using ladder logic & timers

nope... this is a real world application. Our company is evaluating a switch from PIC microcontrollers to an inexpensive PLC (smart relay).

RE: HELP! complex pulse using ladder logic & timers

From your schedule, you'll need a counter.
After 4 cycles of 50 - 100 ms, you deactivate the 50 and 100 ms timers and activate the 300 and 100 ms for one cycle.

However, the schedule you have on top does not match the software comments... so I'm not sure what you really want.

RE: HELP! complex pulse using ladder logic & timers

TY for the suggestion about counters. I hadn't thought of combining counters with flash timers. However, I'm unsure where to put counters in the ladder logic to turn flash timers on/off.

About the pulse schedule not matching the ladder logic & what I really want. What I want is the pulse schedule & I tried to implement using flash timers in ladder logic (but failed). So I'm wondering if the "flash timer" approach is invalid for creating a complex pulse like this.

I think that the Boolean (for the ladder logic) looks something like this:

I01 = T01 (off delay timer: for total duration = number of pulse repetitions)
T01 = T02 (flash timer: 600ms on then 400ms off ONLY WHILE off delay timer is ON)
T02 = T03 (flash timer: 50ms on then 100ms off ONLY WHILE 600ms timer is ON)
t02 = T04 (flash timer: 300ms on then 100ms off ONLY WHILE 600ms timer is OFF)
T03*(T04+T01) = Q01 (output on ONLY WHILE designated timers are ON)

RE: HELP! complex pulse using ladder logic & timers

You'd need a bit to define if it's the first cycle (50 and 100 ms) or the second.

At the end of the rung you'd add another cycle to the counter.

Inc C1 // for example

If the counter1 equals 4, then set the bit, reset the counter.
Use the counter2 to define how many cycles of 100 and 300 ms you'd need.

In the beginning of the rung you use this bit along with the I0.

RE: HELP! complex pulse using ladder logic & timers

You can use just one counter and then use compare instructions to turn on or off your output. Using this technique you can get some very complex pulses, and changing them is as easy as changing the values in an array.

RE: HELP! complex pulse using ladder logic & timers

TY everyone for all your responses.

Turns out the logic using nested timers actually does work with the TECO SG2 PLC. It does NOT display the complex pulse using the PC interface software (which is all I was using to validate the concept when I posted originally). Apparently the only way to really validate the software logic is to install it in a physical unit (which I ultimately did) rather than rely on the vendor supplied PC interface to the device for ladder program verification. Maybe a different PLC with a better more refined PC interface would be a an apt development environment instead.

Thanks again

RE: HELP! complex pulse using ladder logic & timers

I've kinda given up on Teco. Their documentation and execution is simply horrid. They rewrote their manual and, sadly, removed some things that were clearly described in the first revision and added more obfuscation.

Keith Cress
kcress -

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!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close