M340 analog input samplig

[Cuschie_c]

Hello, 

with Control Expert I have some problem to understand how to sample AI value connected on AMI0810 with M340.

(now i have a Siemens S7-1200 simulating a ramp up and sending it every 2 seconds trough an analog output to an analog input of the AMI0810 in 0-10v or 0-20mA) 

check next image for the wave pattern, the ramp up duration is about 50 ms, then the value go back to 0 for 2 seconds

 

I've disabled 7 analog input, to have faster sampling rate from the module (1ms + 1ms for channel active)

created a FAST task cycling every 5ms, where:

if the RAW value of the AI (%IW0.6.7 in that case) is growing and is greater than X and lower than Y, store that value inside an array
I suppose to have at least six to ten stored value before the next AI signal will arrive.

but the stored value are all the same (or two different value), doing a trace on the input signal I cannot see the curve sent by the Siemens PLC, but only 3 step

 

 

Seems strange the timing into the trending tool, seems like 3ms every step,

 

With the oscilloscope I can confirm that the output from siemens is OK

I cannot understand what I'm doing wrong for sampling the data (the program seems working correctly, just the analog value seems not updated every cycle) 

[Trinxs1 · Accepted solution]

Worth checking.  Is the AI card updates allocated to the master task (default setting) or the fast task?  Click on the AI card in the rack image and check that the update task is correct.  If it is synchronised with the master task it will only update at the master task rate.

[Cuschie_c]

thank you,

I resolve the problem on Thursday morning, (then I come back today to update the post, and found your reply).

As you said the AI updates were allocated to Mast task, changing it to FAST task had resolve the problem (probably also select "fast" cycle will improve the performance, but I'm not sure about the difference).

My error was think the Mast task is "fast enough" to sample the data because i set it to Cyclic and not Periodic.

BR,

Christopher.

[Trinxs1]

Where ever you can use periodic for the master task.  it tends to give a more consistent response and you can then measure the load on the CPU via System words.

Note it you make the period too short for the periodic it effectively becomes cyclic but it is worth managing this better.