Pulsing bit

[Zwall]

Hello everyone,

I am new to unitronics but not automation and ladder. I worked quite a lot on Siemens lately but at the moment I am lost.

I can't manage to find a way to simply make pulsing bit every second, I just want to convert a flow of liquid coming from a captor into a volume.

I tried to use the timer TP but it seems like it makes a 1 second pulsation and a pulsation every 1 second. Could someone enlighten me on this mystery? 

[Flex727]

Not sure exactly what you mean by "pulsing". Do you want the bit on for one scan or for one second? If one scan then use a Positive Transition contact of either the one sec System Frequency bit, or use a self-resetting TON timer for frequencies other than 1 sec.

Here is an example of a self-resetting timer. Place anything you want to have happen on the single scan to the right of the positive transition contact in rung 2.

34 minutes ago, Zwall said:

I tried to use the timer TP but it seems like it makes a 1 second pulsation and a pulsation every 1 second.

This makes no sense to me, but if you want a pulse of one second duration, then you activate the TP timer with a transition contact and the Timer Out will be on for the preset time each time it is activated.

If you want a one second pulse every 3 seconds, then combine the two techniques above.

[Gabriel Franco]

There is a tag named Frequency.Frequency 1 (s) you can use with NO contact 

[Isakovic]

If you need bit for one scan every second you should use transition contact in Gabriel's example, Felx's example will also work with normal contact. I don't know why this function was omitted from system bits in UniLogic, it is present in VisiLogic and I believe it is often used.

Now I have a question here which method is best practice. In documentation for VisiLogic it is suggested to reduce the number of transition contacts, so I personally use one timer like Flex posted but with normal contact wherever it is needed in program. Is this still an issue in UniLogic or we can simply use frequency bit with transition contact?

[Zwall]

Thanks a lot for the help, and sorry for the bad English or the nonsense, I was so frustrated, I wrote the message just before leaving totally furious...

It worked for me, I finally managed to get the bit flickering every 1 seconds for 1 scan.

[Flex727]

7 hours ago, Isakovic said:

Now I have a question here which method is best practice. In documentation for VisiLogic it is suggested to reduce the number of transition contacts, so I personally use one timer like Flex posted but with normal contact wherever it is needed in program. Is this still an issue in UniLogic or we can simply use frequency bit with transition contact?

I think the only reason for this warning is that there are only a limited number of transition contacts available. This is, of course, due to the extra memory requirement for a transition contact (the PLC must "remember" the previous state) and that set aside memory is finite. As it is, there is enough memory for at least a couple hundred transition contacts (maybe 256? I don't remember) so the programmer would rarely run out (though I have in the past). If there is another reason to reduce transition contacts, I certainly would like to know.

In the example I provided above with the self-resetting timer, I would prefer to use a positive transition contact even though a direct contact would only be on for a single scan anyway. This is because it is more clear to another programmer, or myself at a later date, exactly what the logic is doing.