Real-Time > 1ms

Question 01: Which PLC, accepts clock base of time less 1 ms ?

Some PLC's let you have access to Real-Time values smaller than 1 msec!

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By Terry Woods Feb-23-02.

Question 02:Some PLC, possible determine fix SCANTIME. (special register)

Please more important for determine the hadrware.

Reply any brand and models. Tranks helps, cheats.

I dont have any idea how one could use a clock cycle contact that reacted 5 to 8 x faster than the program scan time.


The shortest clock cycle bit I am aware on any PLC I've ever worked on, is 50ms.

Dislcamer: Experienced only with AD, Omron, Idec, TI & Siemens. GE 90-30. No 1ms clocks in any of these.

Is this a in reference to a PLC made by Cray?

Sorry,

Mike

Perhaps Terry will make an appearance and define "some"?... utoh

I'd settle for just an appearance...

beerchug

-Eric

ControlLogix has a 1-millisecond timebase on it's ordinary Timer instructions.

There's also a free-running system clock that is used for motion co-ordination and I/O timestamping whose timebase is 1 microsecond.

Logix interrupt-driven behavior is too big a subject for a random inquiry about "fast clocks", so I'll hold off the long explanation.

Giddings & Lewis allows you to schedule ladder in a servo task (i.e. a true timed interupt) at intervals of 1,2,4, or 8msec in their Pic900 family. It's very fast and very deterministic. Since it's a true timed interupt, you have to be careful when passing data back and forth between the main ladder file and the task file, but they give examples of handshaking to insure valid data.

They also allow hardware interupts, and a periodic timed task in 10msec increments, but it isn't as deterministic since it isn't a true interupt i.e. it will wait for the main task to finish an instruction or I/O update.

This is all in addition to their powerful motion control instruction set.

http://www.giddings.com