Scan time

1、PLC scan time is changeable.You can set 1ms ,2ms,10ms,100ms and etc. But soe scan time should be less than 1ms .

2、Different PLC have different available scan time and differe compancy 'S plc is different .

For example ,S7-200 ,S7-300 and S7-400 ,their fastest cycle time is different .

Minimum scan time will depend on the PLC and your program. Some PLC's are quite fast while others aren't, it also depends on the instructions used and program structure. I would expect to see 10 to 50 millisecond scan times with most of the PLC's we work with, although we have some going to 100 or so millisecends. One of the fastest was a Fuji which was at 2 milliseconds with a sizeable complex sorting system.

Cheers,

Trevor.

NEERUVTI-

From the AVG/EZAutomation EZPLC Hardware Manual:

www.ezautomation.net

Other manufacturer manuals should give you a similar explanation.

3.8 I/O Response Time

I/O response time is typically defined as the time required for the control

system to note a change in an input point and update a corresponding

output point.

In a majority of the applications, the processor of a PLC responds

practically instantaneously to this task. There are some applications

that require extremely fast I/O scan times. The following four factors

affect the I/O response time of a CPU:

1. The point in the scan period when the field input changes its

state.

2. Delay time for Input module to change state.

3. CPU scan time.

4. Delay time for Output module to change state.

Normal I/O Response Time

See the diagram above. The I/O response time is minimum when the I/O

module gets the input change before the Read Inputs portion of the Ladder

execution scan cycle. In this case the input status is read, the logic program

is solved, and the corresponding output point gets updated.

The total I/O response time is calculated as: I/O Response = Delay in Input

module + CPU Scan Time + Delay in Output module

Maximum I/O Response Time

The I/O response time is maximum when the I/O module notes an input

change after the Read Inputs portion of the Ladder execution scan cycle.

In this case the input status gets noted only in the following Input scan. The

diagram shows an example of I/O response timing for this condition.

The total I/O response time is calculated as: I/O Response = Delay in Input

module + 2 times the CPU Scan Time + delay in output module.

3-11

How to get the best I/O Response time

Using Interrupt subroutines and Immediate I/O instructions is the best way

to optimize the I/O Response time of your EZPLC system. The immediate

instructions update the I/O points during the ladder logic program execution.

See the EZPLC Software Manual for detailed description of Immediate

instructions. The diagram shows how immediate input and output instructions

affect the I/O response timing.

The total I/O response time is simply calculated as:

I/O Response = Delay

in Input module + Instruction Execution Time + Delay in Output module

+ Instruction Execution Time = Immediate Input Instruction Execution +

Immediate Output Instruction + Time for Execution of all Instructions inbetween

The total I/O response time for an external interrupt and a subroutine is

calculated as:

Delay in Input Module + execution of subroutine + delay in

output module. As an example, upon an interrupt you can read the status of

an input bit, perform a logical operation on it based upon the value of some

other registers, and turn on an output in less than 50μs.

Dear Brother,

Good Morning.

Thanks for the detail input.

Well, what ever discussions you have written is all regarding the PLC scan time. Well how about SOE punching.

On what factors does it depend?

PLC scan time in crude language can be defined as: I/P entering the system+instrusction execution time+o/p going to field which is generally of the order of 100ms (I have seen in most of the cases).

How about scan time?

Could you clarify further?

Regards,

Neeruvti

I have taken up enough "space" with my replies.

I do not require such instantaneous "alarm" reaction in my industry. If my process reacts within 1 to 3 seconds, the process is successful.

Try searching the referenced web site at Rockwell Automation.

http://literature.rockwellautomation.com/idc/groups/public/documents/webassets/browse_category.hcst

Hope you find what you need!

Thanks buddy.......

Found this:

http://literature.rockwellautomation.com/idc/groups/literature/documents/pp/1756-pp007_-en-e.pdf

CR4 Admin: Removed broken link