high speed counter confusion

Here it goes...I'm still on the new side of PLC Programming, so please bear with me.

I am trying to write a program utilizing a flow meter that pulses at 10 kHz. I have AB's ControLogix for a PLC along with their High Speed Counter module.

Here's what I want to do:
Turn on an output on the High Speed Counter, reach a certain count and use the counter to turn off it's onboard output.

setting the count and turning off the output is easy enough, I think. Just set the config values...

Unlike a real man, I've been reading the instructions for the counter.

NOW I'm really confused. HOW DO I TURN THIS STUPID OUTPUT HOT??

What you have described sounds weird to me.

It just seems kinda strange to me that a module that is supposed to be providing input info to the CPU is also controlling outputs - apparently, independent of the CPU?

Just seems kinda weird to me.

But, if it is as you describe, then it sounds like you need to determine the nature of that output (sourcing? sinking? either?) and then identify the terminals associated with the output, and then make the appropriate connections between the terminals, the load and HOT/NEUTRAL.

I'm not sure about controllogix, but both the Micrologix and SLC platform HSCs have commands that let you place certain outputs (selected ones for the micro, card-based for the slc) under direct control of the HSC itself, turning off or on at certain presets.

The reasoning behind this is that the HSC is so much faster than the scan time, the transition might be overlooked if not placed under the control of the HSC circuitry itself.

As for the question - sorry, I dunno I've tangled with the HSC on a micro numerous times, and finally just put the output under normal PLC control and used compare instructions with the HSC setpoint. But in my application, a little overshoot wasn't horribly critical. You are the only one who can make that determination.

Good Luck!

TM

I haven't used that counter, or controllogix, but I have used the PLC-5 and SLC 500 versions. In those systems, you have to configure an output turn on count, as well as an output turn off count. you could, say, go on at 50, off 100, on 150 off 200, etc, to get a square wave. But at some point, because the on and off config values are limited in number, you have to reset the count to zero and start the count again.

I haven't worked with the Control Logix HSC, but with the SLC HSC, if the start value for a range was greater than the end value, the output associated with the range would behave as you want.

Terry,
The high speed counter module has outputs that can be controlled by the module, outside of the restrictions of the PLC scan. You can think of the HSC as a PLC within a PLC.

Thank you all for the feedback!

Maybe a little more detail of what I'm trying to do will let you all know how I got myself into this mess.

I'm trying to have a flow meter control the opening and closing of a valve. batch control at it's simplest level.

Please tell me if this makes sense:
The biggest problem I'm having is trying to turn on the flow with a delay. This means I don't have any pulses to count until I turn on the output. But... If I use my preliminary conditions to change the accumulated bit value to match the start bit value, the valve will open (output will turn on) and the flow will start until it reaches the off value, and then can be reset to 0 to await another cycle.

Can I do this?
Thank you all for the support!!

Once again, using the SLC HSC as a model. In that one, you have control bits to reset the counter and to inhibit counting (Hold). These bits can be controlled from ladder logic.

For your situation, use a start value of xxx and an end value of zero, where xxx is the number of pulses corresponding to the volume you want to pass. Have your ladder logic hold the counter at zero value until you're ready to start the flow. Then turn off the Hold bit. That should turn on the valve immediately, and turn it off when the HSC accumulated count reaches xxx. Once the valve is off, you have plenty of time for the ladder logic to reset the HSC and reassert the Hold bit.

Note that I'm making the assumption that the Control Logix HSC has the same capabilities as the SLC HSC. I'm also assuming that when the HSC is in a Hold state, the outputs are turned off. If either of those assumptions are incorrect, you may have to tinker with the details, but I think the concept is sound.