RSLogix 5000 One Shot

[nickjeffers2006]

I am new to programing and a mechanical engineer by background so please don't think to badly of my for not knowing the answer already. Can someone please help me understand how the one shot instruction works? Example: I have a rung with a normally open input as the first instruction. At the end of the rung I have a timer. I want to make the input condition true and hold it true for several cycles of the timer. So when the input goes true for the first time, the counter starts. When the counter finishes another action happens in a later rung. The counter is then reset without ever resetting the orginal input condition (has remained true since the first activation). If I have a one shot between the input and the timer, if the timer is reset will the timer start timing again (without having reset the input, meaning the input and the one shot are still activated). Or do I need to come up with some other plan? Please help.

 

[NWBeaver]

The logic to the right of a ONS is only enabled for one scan, when the rung input conditions are true.

So, if you have a ONS in front of a timer, the timer will run for one scan, unless you have some addition logic in a branch around the ONS.

You mentioned timers and counters are you using both, or just a timer?

 

[NWBeaver]

I meant to say additional logic, not addition logic, sorry.
An example would be using the timer done bit in parallel with the ONS.

As far as resetting the timer goes, if the input conditions are still true the timer should reset, and resume timing.

 

[smokinotes]

No the Timer will not restart timing until the ONS or the input goes from false to true again. I not sure what you mean by holding the input true once the timer starts timing. Is it a discrete input or an internal bit?

 

[panelman]

When I was learning I found that a little test pile of hardware was very useful for answering this sort of question (and a lot more)

I recently did a fairly complex chemical dosing system (lots of pid & analogue), the client wanted lots of changes after commissioning and I used my test rig to develop the more complex changes rather than doing them on live plant.