Scan rate: 1 second?

m.nazish

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• Oct 8, 2008

• #1

Why do we normally use 1 second as the scan rate to scan dataitems of cards in PLCs? Does it have any relation with the devices performance issues? PLZ help!

 

jvdcande

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• Oct 8, 2008

• #2

Why do you? Scan rates here are about 10-120ms depending on the programs. What PLC are you talking about?

More detailed info is needed to help you out.

Kind regards,

 

m.nazish

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• Oct 8, 2008

• #3

for PLCs like PLC5, MicroLogix etc.

 

OZEE

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• Oct 8, 2008

• #4

I have NEVER seen a scan rate that slow. Typically for us, it will be 10-40 ms.

 

tragically1969

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• Oct 8, 2008

• #5

Perhaps he is talking about the rate at which they are bringing values back from the analogue card channels into the ladder etc. rather than PLC Scan times ?

 

m.nazish

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• Oct 8, 2008

• #6

If we keep the scan rate as 60 sec, Would there be any devices performance issues? I want to know why scan rate is normally so slow. It just depends on the program??????

 

Oakley

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• Oct 8, 2008

• #7

Also depends on the process you are monitoring/controlling.

 

rdrast

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• Oct 8, 2008

• #8

m.nazish:

You really need to explain better your system, and what you are talking about.

A PLC5, an SLC500, a MicroLogix, a Logix, or any other PLC I can think of would never have a CYCLICAL Program scan that long... Now, if you are talking about a timed task, or a periodic interrupt task, perhaps.

If you are talking communications to an HMI, maybe.

If you are actually talking the CYCLICAL (LAD-2) program scan, that's a problem.

 

OZEE

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• Oct 8, 2008

• #9

m.nazish said:

If we keep the scan rate as 60 sec, Would there be any devices performance issues? I want to know why scan rate is normally so slow. It just depends on the program??????

Click to expand...

Please post a screenshot showing exactly what you're referring to.

Tell us more about your process - which PLC, how many I/O, how many analog, etc... Without knowing what you're doing, we can not make any evaluation about "performance issues".

But like several of us have said, there's absolutely no reason for a 60 sec scan rate...