High Speed Pulse Count

[fuzail]

Hi,

I am trying to count rate of pulses in given time period (say every 5msec for 2 minutes). The pulses arriving might have max frequency of 1000 pulses per second. Is there a way to record the rate of pulses using PLC. Is high speed counter the solution. Also i would prefer m340 PLC by schneider. Does the scan time of PLC has impact on my counting if yes any pointers how to handle it ... ?

 

[Steve Bailey]

To count pulses at 1kHz you will need a high speed counter module. The high speed counter modules for many PLC models include rate as well as counts in the data they provide to the PLC. The scan time of the PLC will determine how frequently the data from the HSC module is refreshed in the PLC.

 

[fuzail]

The scan time of the PLC will determine how frequently the data from the HSC module is refreshed in the PLC.

It mean that HSC will catch all my pulses (at high frequencies) but update into my ladder logic would be according to PLC scan time. Then scan time will not filter out my pulses it just delays updation of pulses into ladder logic ... correct ?

 

[Steve Bailey]

That's correct.

 

[fuzail]

@Steve thanks for info ... Will check into HSC modules supported by m340 PLC and comeback if need any further support

 

[fuzail]

Hi,

To add more detail, i want to store rate of pulse count (say every 100msec for 2 min) in PLC memory (for further calculation).

In high speed counters there is 'event count mode' where counter assesses the number of pulses applied at the input, at time intervals defined by the user.

My worry is to capture(in registers) these counted pulses, for further processing. Is there any method where by i can look at pulses counted at user defined intervals.

I am planning to use m340 PLC (schneider) with BMX EHC 0800 counting module.

Kindly help.

 

[fuzail]

Any advice pls ...

 

[V0N_hydro]

have you read the manual for the module?

http://www.guilleviniag.com/downloads/Products/Schneider/M340/Manuals/M340 EHC 0800 Manual.pdf

Why won't event count mode work for you?

 

[fuzail]

@ V0N_hydro ...Iam caught up in this question of how do my PLC (with certain scan time) be able to catch the counter_current_value. Since counter module would work on different scan time (if not then it cannot capture high freq pulses), how do I capture and bring that counter value to my ladder logic.

The manual says "The counting register is updated at the end of each interval with the number of events received"
Good.The count is stored in counter_current_value (Am I correct ?)

Further more it says "It is possible to optionally use the IN_AUX input over a time interval, provided that the validation bit is set to 1. This leads to restarting the event counting for a new predefined time interval"

As I said I want this repetitive counting (count every 100 msec for 2min). Now how to generate/use this IN_AUX input so as to acheive this.

P.S: Never used counter module till now, trying my hand over it for the very first time.


Thanks

 

[V0N_hydro]

It doesn't sound like you want to use an input to the PLC, IN_AUX, to determine the timer interval. You want to have a fixed time interval of 100ms.

So you can either set the interval to 100ms, and you will have to read the counter manual to determine which configuration register is used to set the user defined interval period, or you could use the IN_AUX input with a rising edge every 100ms.

Probably one of the module status bits will tell the PLC program when the user defined period has expired and count has been updated and then you can read the new count in the program.

You should wire the module up and start experimenting with it.

 

[fuzail]

Yes true i want to count for fixed interval 100msec for about 2min.

Also as you suggested I will start experimenting with module.

Thanks