Refresh Function in AB Micrologic 1200

[ian.smith7]

Hi All
Ive have converted a program from an old Mitsi F1 to an AB MicroLogigic 1200.
The program uses the High Speed Counter function and switches a series of outputs based on Limit tests of the ACC value. On the rung following each Limit test I have placed a Refresh function to update the I/O.
In order to reduce the processing time I have made the Refresh conditional on the limit test output being on.
My Question is will the Refresh function be active in the same scan that the Limit test is FIRST resovled as true because if not then I might as well take it out.
I suppose I am asking if logic solved as true in rung 3 of the scan is acted on as true in rung 4 of the same scan?
Thanks
Ian Smith

 

[moltra]

Please post the file or a screen shot of the files, so we can see how it is programmed.

Moltra

 

[ian.smith7]

Hi Moltra
I'm afraid I cannot Post the logic because I dont have the software at home (only at Work).
Will this do?


-----------|LIM HSC:0.ACC 47&56|-------------------O:2/0


-----------|O:2/0|-----------------------------------REF


O:2/0 is on when HSC:0.ACC is between 47 & 56.

By the way I edited My first post.

ian

 

[Sergei Troizky]

You have to use IOM instruction, which only refreshes outputs.
The REF instruction performs all interscan tasks, including external communications, and takes lots of time.

 

[ian.smith7]

Hi Sergei

I looked at the IOM Instruction but it only works on the I/O in the Base unit and for other reasons I am using outputs on an extension unit. The solenoids being driven by these outputs are 110v AC and the relays in the output unit have a limited life. It is easier to replace an extension unit rather than the base unit.
ian

 

[bernie_carlton]

AC (triac) outputs probably would not have benefitted by the Immediate Out instruction anyway. Many triac circuits only fire at the next zero cross. That can be as much as 8ms away or as near as 0 (60 hz).

 

[tom_stalcup]

Hmmm... Thread hijacking in progress.....

Bernie,
When you say "zero cross" are you talking about when the AC sign wave crosses thru zero? I've never actually looked at how a triac works, but that's what I think you are talking about.

inquiring minds want to know.....

 

[tom_stalcup]

Nevermind Bernie... Just did the math.... 60 cycles per second.... two zero points per cycle... 8.333333 msec.

But I still don't know exactly how a triac works....

 

[mellis]

Try www.howstuffworks.com if you dig a bit you'll get a pretty good explanation. Actually, I was expecting fluff and was surprised at the detail available.

In the context of a PLC output, it works like this:
Command to turn on output arrives at I/O card, triac fires.
Command to turn off output arrives at I/O card, triac stays on until voltage crosses zero.

 

[tom_stalcup]

Hmmm... I'll have to dig thru that link too... I'd found THIS spot, but I couldn't really correlate that to why the triac only fires on the zero points on the cycle.

 

[bernie_carlton]

Actually the zero point TURN OFF is almost a given since in that respect they function like back-to-back SCRs.

It's the TURN ON which can vary depending on the nature of the firing circuit. Some are 'Random Turn On' which fires as soon as it's enabled assuming the sine wave is already at a high enough level (a few volts). There is 'Zero Cross' turn on which helps in some circuits limit the initial current rush. A few have 'Peak' turn on and are intended for very inductive loads like a transformer.