Is 314C-2DP fast enough?

Hi all,

I have another thread that has evolved from the original subject into a new question so I thought I'd start a new topic.

I want to be able to count about 1000 pulses over 9 seconds.

Would this be possible using a 314C-2DP? This PLC reports that it has a speed of 0.1ms/1000 instructions. It also has "4 channel counting and measuring with incremental encoders 24V (60Khz)" not sure what that last bit means fully but am I right in thinking that if it ends up not being fast enough I could somehow configure 4 built in high-speed counters to do the job??

Any help on this would be greatly appreciated. I know that scan time is dependant on program size, the program isn't particularly large (I know that's not very descriptive!!)

Many thanks for any suggestions/pointers you can give me

Sounds like the interrupt input will do the job. Say 10 instructions to increment a count value inside the interrupt routine = 1 microsecond to execute.

OK so that means you need a scan time of less than 4.5mS, otherwise you will miss pulses. It's not just the headline 0.1mS/1000 instructions that contribute to scan time, you also have I/O to read, comms with the programmer etc. The S7 manuals have the figures to allow you calculate this figure, but gut feeling is it is a bit 'tight'

Interrupts are fine but remember that they also add to scan time. It's not just the run time of the code, there is also an overhead, which Siemens document, which is the time taken to stop processing the main code, jump to the interrupt, and return to the main code and tidy up. This overhead can be obtained from the S7 manual.

Using the high speed counters will be easier to impliment if you are just counting pulses.

The impact of using interrupts on the main program scan depends on the time between interrupts, and the run time including overhead.

As an example an interrupt with a run time of 200uS called evrey 300uS will triple the main program scan time compared with no interrupts (OK an extreme example)

So try and use the High speed counters, in my experience it's easier than interrupts if it does everything you want.

OK, Thanks for the tips.

So am I right in thinking that the 314C-2DP has 4 high speed counters that I can use or am I going to have to buy a separate card??

Cheers