HSCE in SLC slowing down PLC scans

[camman]

I have 4 HSCE cards in an AB SLC 5/04 PLC. The counter cards are reading 0 to 10KHZ inputs from Micromotion flow meters and then the program totalizes the flow using the rate from the HSCE.

The problem is that the PLC scan cycles are so slow (due to the HSCE program rungs)that the PID blocks can't control the flow.

I have looked over the program and it looks like the HSCE cards are being initiallized every scan (multiple MOV blocks putting values into M0:6.0 ... M0:6.41 for each card, every scan cycle). The program then reads the values from the HSCE cards, (I:6.1, every scan).

My question is - Do all of these HSCE values need to be initiallized every scan? Reading the manual for the HSCE it looks like this only needs to be done once and then read the input every scan.

 

[OkiePC]

Any time the M0 or M1 files are accessed, the scan time will take a big hit.

Reading the standard input data area (I:6.1) should not cause any extra scan time, unless you're doing it with an interrupt instruction.

You should only have to write to the M0 files when there is a need to change the card configuration.

Often, this is only done on first scan (XIC S:1/15) with a COPy instruction.

You might want to put an XIC with an internal bit in parallel with that so you can manually trigger the copy in case the card configuration needs to be changed without restarting the SLC.

 

[camman]

I am going to setup the program to run the HSCE configuration once, at the beginning of the program.
I recall somthing about problems with card faults when the guys first ran this program, several years ago.
So I am also going to read the status from the HSCE, I:6.0, and if there is a fault, I will reload the configuration.

Here is the configuration for HSCE card in slot 6:

M0:6.0 2
M0:6.1 32348
M0:6.2 1
M0:6.3 2
M0:6.4 2
M0:6.5 2
M0:6.6 2
M0:6.7 2
M0:6.8 0
M0:6.9 2
M0:6.10 0
M0:6.11 1500
M0:6.12 0
M0:6.13 0
M0:6.14 0
M0:6.15 0
M0:6.16 2
M0:6.17 1
M0:6.18 2
M0:6.19 3
M0:6.20 4
M0:6.21 5
M0:6.22 6
M0:6.23 7
M0:6.24 8
M0:6.25 9
M0:6.26 10
M0:6.27 11
M0:6.28 12
M0:6.29 13
M0:6.30 14
M0:6.31 15
M0:6.32 16
M0:6.33 17
M0:6.34 32767
M0:6.35 0
M0:6.36 0

 

[Ken Roach]

My rule of thumb is that every reference to a Module file (M0 or M1) adds about a millisecond of scan time. I always try to do M-file references with a COP instruction and condition them to run only periodically or on-demand.

With multiple counter modules, and multiple MOV instructions, I can see where the controller might see increased scantimes. Your plan is a good one.

 

[JeffKiper]

Look at the Spectrum Control cards they are designed for counting pulses from flow meters.