Using Micrologix1400 embeded DI for pulse input flowmeter

[ling]

I have one flowmeter. rated flow range is 100L/Min, and 1L/Pulse.
I need to hook it up to micrologix 1400 embeded DI to read flowrate. Will a normal counter work or I need to use HSC and how?
Can anyone help? I read some old posts and found it not easy to follow.If someone can provide some sample program, I would really appreciate it.

 

[Tim_Turner]

I do not believe you have to use the HSC. 100L/min max flow and 1L/Pulse is only 100 pulses/min max.

There are probably hundreds of ways to do this and everyone will have their own method.

my starting approach might be to use a TON you could simply start timer when input turns on. the Next time it turns on record and reset timer, and do the math. ie. 750 mSec between pulses in this case with it being a nice round 1pulse = 1L then you can do .75secs/pulse x 60secs/min= 45 pulse/min x 1 L/pulse = 45L/min(since pulse and liter are equal you just have to do .75x60= flow rate.

For a totalizer i would just add up each pulse and divide out by the units they want totalizer in.

I will try to give a sample code later

The big question wil become are the pulse voltage within the readable range of the DI input. ie. if you have 24vdc input version of the ml1400 are the pulses actually 24vdc or something like 7vdc if this is the case you may need to use something like an opticoupler to get voltage high enough to trigger the input on the ML1400

 

[Tim_Turner]

did a little fast checking..
on a micrologix with 24vdc inputs.

on standard inputs (inputs 12 and higher)
on state is 10...24vdc
off state is 0...10vdc

on the high speed inputs (inputs 0-11)
on state 4.5vdc... 24vdc
off state 0....1.5vdc

 

[Tim_Turner]

Sample code. you may have to add some conditions such as if flow greater then 100L/min then alarm etc.

For a totalizer I would not use the flow rate, I would simple add pulses since it is 1 pulse =1 Liter.

https://drive.google.com/file/d/0Bx9rtb9aSnnSOTJXdXAwZ3l3NG8/edit?usp=sharing

This code was a quicky and hard to emulate so you may find glitches and need to add conditions for the execution.

 

[nwboson]

The quick answer to your question is: YES a regular 1400 digital input to a counter will work.

If you figure the scan time of a ridiculously slow 1400 is 100mS (you should be able to beat that no problem unless you are doing a LOT of math), that means you can scan a digital input up to ten times per second. Don't forget to turn off input filtering - and don't forget the Nyquist criterion that says you should cut that number in half to eliminate aliasing. So a reasonable rule of thumb would be an input changing 5 cycles per second will work fine without using the HSC.

 

[ling]

Thanks a lot!