Rate Counter

I have a machine that produces 1 pulse per each part it makes. Max input is 100 pulses per minute or 100 parts per minute.
I need a program to produce how many parts I am making or the rate I am making parts at for 1 hour.
I made a counter, counted parts for every 1 sec and multiplied by 3600 for hourly rate.
I am not sure this is the best way. Results are either 3600 or 7200 pph.
I am using a Micrologix 1400.

Try capturing the time between parts or the time to produce a fixed number of parts.

For example if you measure 750 milliseconds to make a part, your rate is 1/.75 or 1.333 parts per second or 4800 parts per hour. Pick a number of parts that gives you a reasonable update frequency. In the example you recalculate the rate every .75 seconds. If you timed two parts you would recalculate every 1.5 seconds.
The PLC's internal clock will probably give you a more accurate time than its timer functions.

Steve Bailey said:

Try capturing the time between parts or the time to produce a fixed number of parts.

For example if you measure 750 milliseconds to make a part, your rate is 1/.75 or 1.333 parts per second or 4800 parts per hour. Pick a number of parts that gives you a reasonable update frequency. In the example you recalculate the rate every .75 seconds. If you timed two parts you would recalculate every 1.5 seconds.
The PLC's internal clock will probably give you a more accurate time than its timer functions.

Click to expand...

+1 to this. It will give you a fresh number as soon as you complete a part. It will be more precise. It will also show every little variation, which can be a good thing and a bad thing. If I have a process that is a little inconsistent, I will still calculate it this way, and then do a first order filter or average a few of the most recent results. If the process is consistent and steady, I don't bother with that. The quick feedback can be very useful for making adjustments that impact cycle rate...you know right away if you made it better or worse.

Counting parts per second is going to be very imprecise; you will either count 1 or 2 per second, which is why you're seeing either 3600 or 7200 per hour.

It is far more precise to count milliseconds per part.

You can use something as simple as a Timer On Delay (TON) instruction with the timebase set for 1 millisecond, or you can use the controller's free-running clock, or you can use one of the fast inputs and the Discrete Input Interrupt (DII) feature.

Start with the simple timer. Each time the pulse comes in, use a one-shot to Reset the timer, divide its accumulated value by 1000.0, and you will get a floating-point value in seconds.

As the previous example: 3600.0 seconds per part / 0.750 seconds = 4800.0 parts per hour.

+1 Steve