About bus cycle time and analog input sampling period

[kak]

Hi experts,

I'm new to PLC programming so I need your help..

Now I have one M251 dPAC, DI, DO and AI module each. So I want to know analog input sampling rate in PLC.  AI module's sampling rate is 1ms (It seems not to be changed) and TM3 busCycleTime is 50ms. Analog input type is set to VTQREAL type, I can watch analog value change by time value. 

When I set busCycleTime to 50ms, It seems like analog value changed about 250ms cycle. And When I set busCycleTime to 200ms, It seems like analog value changed about 1s cycle. Why analog input value updates 5 times longer than busCycleTime? I can't understand this..

Please anyone explain this and provide any documents or references about this.

[mohamedriswan]

Hi Kak,

Regarding the bus cycle time 

When the bus cycle time is set to 50 ms, the maximum frequency of the modulo event, occurring every 5 ms, results in a value change cycle of 250 ms.

Regarding the AI module Sampling rate change.

You can adjust the sampling rate of the AI by accessing the AI module properties and switching the type from "Not used" to your desired parameter (e.g., voltage or current). This action will reveal a drop-down list, allowing you to set the sampling rate to either 1 ms or 10 ms.

[kak]

Thank you for your answer, @mohamedriswan 

But I still can't understand it. What is the maximum frequency of the modulo event? And why is that occuring every 5ms? Is that related to conversion time of AI module? Can you tell me more detail?

And about AI module's sampling rate, maybe TM3AI2H module I'm using can't change sampling rate. Or maybe I'm missing something. 

[mohamedriswan · Accepted solution]

Hi Kak,

1)The frequency of the modulo event is at a maximum 1 every 5ms.

2)The occurrence every 5ms may be related to the conversion time of the AI module, as this time interval might be necessary for the module to process the signal. This relationship could be a factor in ensuring accurate and timely data acquisition.

3)Yes, the AI Module that you are using has having 1ms sampling rate, we can't change it.

[Eric_Coudurier]

Perhaps it is a little bit too late to answer this question, but better late than never, and the answer may be of interest to others.
In fact, the module's hardware CAT includes an indication factor that triggers information based on a bus cycle number, which is fixed at 5 and cannot be modified. The value is therefore updated every 5 cycles, i.e. 250ms for a 50 ms cycle (5 x 50 ms).