GF 2536 + Micrologix 1400

[sapoleon]

Hi all,
It's been a while, but I was working in another area, and not touching code...
I'm back... with troubles

I have a Signet 2536 square pulse flow meter connected directly to a Micrologix 1400.
I chose that PLC because of the HSC, although they are not needed. (The speed I'm sensing has a max input of 150Hz).

And my trouble is that I am not getting the inputs in the PLC.

I have connected the Signet with the 10ohm resistor, to the 24Vcc, and I am not reading the input in the PLC.
I checked another input with the same result.
I checked the Signet with an oscilloscope, and I am getting the signals from the instrument.
I checked the input of the PLC with 24Vcc directly and get it without problem...

Do anyone has any sugestion on what to test or what can the problem be?

Thanks in advance.

 

[Ken Roach]

What frequency is your test signal ?

The default input filter on a DC input MicroLogix 1400 is 8 milliseconds, so the MicroLogix won't properly count any signal faster than about 60 Hz.

In the I/O configuration window in RSLogix 500 you can turn down the input filter or turn it off.

 

[sapoleon]

Hi Ken,
Thanks for the quick answer.
I forgot to mention that. Yes I turned off the filter. In any case, I will double check that in order to be sure it's off because that was one of the last things I did...

 

[danatomega]

Sounds like the input (or common to the input) is not connected properly.

 

[sapoleon]

hi Danatomega,

I regret to tell you that it is correctly connected. Like I said before, the input works fine when you put the 24Vcc directly to it.

 

[danatomega]

Sorry, you are correct that your original post did include that information ...

 

[Tom Jenkins]

Sounds like the input (or common to the input) is not connected properly.

I agree. This is probably a solid state output tied to a solid state input. You have to determine if the meter and the input are sinking or sourcing and accommodate that in the wiring.

A quick check is to tie the meter to an incandescent pilot light. Below about 25% full scale you should see the flicker.

 

[danatomega]

ML 1400 manual (page 127) says inputs 0-11 (12 high speed inputs) min on state current = 7.0 mA @ 4.4 VDC (nominal 9.5 mA @ 24 VDC).
http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1766-um001_-en-p.pdf

the ColeParmer manual for the 2536 says to use a 10k pull-up resistor - at 24VDC = 2.4 mA. You shouldn't have seen an input turn on at that level.
a 2.5k resistor will get you closer. But the 2536 is limited to 10mA max. Not a very good match...

 

[sapoleon]

Thanks Danatomega,
That I DID miss... I'll have to check with GF... maybe use the 4-20mA conversor... or a current amplifier with that speed....

Tom, thanks also,
No, those were tied correctly.