20ms Pulse time

I have a pulse counter and the dry contact stays energized for appox. 20ms. It pulses once every 1 to 2 minutes based on how many pumps are started. The processor is PLC5/40E and I am using a 1771 IBD input card.

I wired 24vdc + thru the dry contact of pulse counter which goes back to the 1771 IBD terminal 00 with the 24vdc negative I wired to Terminal.

I'm not able to count the pulses on my CTU or even see the bit light come on the card when it pulses.

I measured the DC voltage with a fluke on record and I get 3.6 VDC max. It doesnt seem like enough voltage activate the bit to make it true.

Any ideas on what I could do to make this work? Is there a 1771 card that will only look at a dry contact instead of a voltage?

Two things:

1. Is your circuit wired per the IBD manual?
http://literature.rockwellautomation.com/idc/groups/literature/documents/in/1771-in053_-en-p.pdf

2. Try another input, maybe 00 is bad.

I did wire exactly the same!

I tested the wiring all the way from the field device to the PLC program using a jumper.

The IBD spec indicates a min. of 10 vdc and the fluke is only reading 3.6vdc

Can you provide information or a link to the 'Pulse Counter'?

20ms? What is your program scan time?

Unless you have that IBD set up to generate a hardware interrupt, you are most likely not going to catch that pulse on a PLC-5 scanning a standard input module*.

Measuring the DC voltage of a 20ms pulse is at best completely useless. Force your "Pulse Generator" relay closed, and see if you get the signal.

*(If configured with low propagation delay, the IBD module itself can see a maximum pulse rate of approximatly 500 Hz, or a pulse with a duty cycle of 1ms on, 1ms off, but the CPU is probably going to miss the input).

The 20ms is the time the contact is closed pulse counter as per the spec.

I attached the scan time. it was 8-10 ms

I also attached the spec sheet of the pulse counter from McCrometer.

I tried to find where I can set up the Hardware Interrupt and was unable.

I hope this additional information will help.