HSCE2 counter problem

Hello, I'm new to this forum and fairly new to PLC's. I have a problem with extra pulses coming in from a turbine meter pulse output to an HSCE2 counter card. The processor is a SLC 5/04, the counter card is a 1746-HSCE2 counter set up for 4 counters(mode 3, class 4). The pulse output comes from kessler ellis BATRTM-3 turbine meters. The problem is that sometimes the input pulse counts double(as two pulses at once). The input is a fairly low frequency(1Hz to 8HZ), I don't use the conter card for rate values. I don't see any grounding issues. I hooked up a pulse generator to the counter card and it worked at any frequency I set it for. Is it a noise issue? Do I need a low pass filter? Is it maybe in my configuration of the card? I just don't know.

Why at all such low frequency signal should be connected to HSC card?

I know that the HSCE2 module is probably not needed in this application. This was setup by someone else and I was called in to look at why the accumulation is incorrect. Can it work at such a low frequency? I see nothing in the user manual that says so but this is the first time I've worked with the HSCE2.

You are possibly getting getting ringing on the pulse transitions or you are seeing noise on the edges of the pulses. The HSCE2 doesn't have a lower frequency limit so that shouldn't be an issue.

I don't know of any onboard filtering with the HSCE2. You need to try and clean up the counter pulse edge. I'm guessing that the pulse from the flowmeter is not a 50% duty cycle, which is probably why the HSCE2 was used in the first place. So if you choose to try some external filtering make sure you don't apply such an agressive filter that you drown out the actual pulse. Also, what is your voltage jumper set to? There is a small overlap to the ranges. If you are in that overlap area, choose the higher voltage. Also, if you can, run the signal as a differential pair. It will tend to be more noise immune.

If you are sure the pulse frequency is never going to go above twice your scan frequency you may be able to do some things with plc logic. But I would try to clean up the input first.
Keith

What is the nature of the pulse signal from the Kessler-Ellis device? Could you be detecting contact bounce? A quick look at the KEP website seems to indicate that the part number you cited is a ratemeter with a pulse output. If so, the HSCE2 is probably overkill. The KEP device may already be doing the accumulation.

Monitor the signal from the BATRTM-3 with a scope to see if there is any bounce that the HSCE2 might pick up as an additional contact closure.