ControlLogix Flashers

Introduction to ControlLogix Flashers

ControlLogix flashers allow for an output to be energized and de-energized at a steady interval.    For example, if we have an alarm horn, you can add a flasher bit in series with the output.   The alarm horn will then energize and de-energize at regular intervals.  Subsequently, this will get the operator’s attention.

With this purpose in mind, we will discuss two different ways to generate a pulse.   First, we will use a simple self-running timer.   Secondly, we will use two timer to give us control of both the “ON” time, and the “OFF” time.    Basically, this will give a “Strobe” effect.

If you are not familiar with timers yet, please read up on this article before you continue.

Self-Run Method

The self-running timer method is the most simple.    In this situation, we will have just one timer that continues to reset itself every second.

Self Running Timer

When the accumulated value reaches 1000, the DN bit goes high.    Obviously, the timer will then shut off.   When the time shuts off, the DN Bit goes low.   When this happens, the timer will start again.

We will use a GRT (greater than) instruction to create the flasher bit.    In this case, the flasher bit will be on for the last half of the second, and off for the first half of every second.

GRT Flasher

Flip Flop method

Another method is to use two separate timers.   This gives us more control of the “ON” time, and the “OFF” Time.    When the first timer finishes timing, the second timer will start.   When the second timer is finished timing, the first timer will no longer be enabled.    At this time the first timer is no longer enabled, it’s DN bit goes false.    In turn, the DN Bit for the second timer goes false.     When this happens, the first timer begins to run again, and the whole process starts all over!   That beings said, it’s a little more complicated than the Self-Run method.   By the same token, the logic shown is exactly how you would wire time delay relays to perform the same action!   Let’s look at the code.

FlipFlop Timers


In either case, you can use the flasher bit in series with any output such as a strobe or alarm horn to get the operator’s attention!


—  Ricky Bryce


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