Question

Hey all. I was wondering at the sawmill where i do some PLC programming they have a bull edger.

There is an outfeed sensor, and what they want is when the outfeed sensor is clear the blades to go back to a certain position and a timer to start for 5 seconds.

When the outfeed sensor is tripped a timer starts for a different application, what i was wondering if there is a way so that when it clears that the blades go to a certain position and the timer to start.

Is there a way i can set a bit so it only reads after the sensor is cleared i was thinking a ONS but i can't seem to get it to run properly it just sticks on.

I was just wondering if there was a way.... thanks in advance


If there is any questions and you use msn you can add me at [email protected] it would be easier to explain to you.

Create a WAS bit. When the sensor comes ON use it to latch a bit i.e. SENSOR WAS ON then use the sensor input with it for you next action.

   Sensor    Sensor WAS       OUT

|----|/|---------| |----------( )--|

Use OUT to reset the WAS bit.

can you explain the was thing a little more please??

There are a couple of ways to do this, the picture shows one example. In this picture the WAS bit is self sealing with a RESET bit to deactivate it. The RESET bit can be any bit that is TRUE after you have obtained the action you needed from knowing the sensor WAS ON and is NOW OFF.

Thanks i got a good idea now of how i am going to go about this.

Great description

I learn something new here every day.
I use latch bits all the time. Naming them a "was" bit is sometimes a much better descripyion.
Thanks Ron