Twido maximum counting speed via ladder logic

I'm working with a TWDLCAA24DRF that is having trouble missing pulses off of a flow meter.

I'm not real familiar with the Twido PLCs but it doesn't look like this setup is using any type of high speed counter and they are just incrementing a variable in the PLC via program scan. The problem is the best I can tell the switching frequency coming from this flow meter is around 3.5ms. Normally I would say this is too fast to be done in a normal program scan, but is there something I don't know about this Twido?

Below is the rung of logic in question

I know zero about the Twidos, but I'll throw out a couple ideas...

Do you know of any change (hardware/software) that preceded the problem? I assume it was working previously? It may have been barely catching the pulses originally. Any additional logic added to the program might increase the scan time enough to affect this. Are the input filters adjustable (like a ML)? Maybe the flow rate is faster than before?



-Eric

My understanding is it didn't work since day one. I was just recently brought in on it. The pumps are a fixed flow.

According to THIS datasheet, the input filters appear to be adjustable. The MANUAL is confusing, but it looks like there are three 5kHz counters available (see 'fast counting' on page 215). Too bad you need four...



-Eric

your controller supports high speed counter if it is set up properly, but it only supports 2. You also only have 2 high speed inputs and the 4 you are showing belong to the hi speed counter. Is there a HIGH speed input card attached? look at pages 249 and 250 of the first manual, it shows what I think you have, though it may be configured wrong or I'm on the wrong track. It also has a count frequency of 5khz, not 20. Right now it looks like they are trying to use the HS counter inputs to Increment a double word. I haven't used this plc before, but it looks like it is misconfigured. Hope the manuals help you


here is the link to the hardware manual

http://download.schneider-electric.com/files?p_Reference=31003914K01001&p_EnDocType=User%20guide&p_File_Id=27461939&p_File_Name=31003914K01001.pdf

here is the link to the software manual

http://download.schneider-electric....le_Id=27462400&p_File_Name=31003914K01002.pdf

I think you guys are helping me verify the problem. Best I can tell unless you are using the function blocks shown on page 459 of the software manual Max posted, you are not using them as high speed counters. Additionally their model has three fast counters which doesn't help since they need four counters.

So I guess the last question is what is the feasibility that with a 3.5ms switching frequency it is accurately counting the pulses using standard inputs? I now see how to check the scan time, but the system is a few hours away and no one there can check it for me. Any educated guesses?

looks like that this contoller support 3 fast counters (5kHz, inputs %I0.2-%I0.4 and one very fast counter (20kHz, input %I0.1), so it can maybe be possible?



You can also define inputs %I0.2 - %i0.5 to latching inputs.

From twido's help file: "Latching allows incoming pulses with amplitude widths shorter than the controller scan time to be captured and recorded"

But for latching, pulse period needs to be longer than controllers scan time*2.