Calculate flow

Hi,

I have a flowmeter and an highspeed counter interface card.

I like to calculate the flow (ex. litre/min) from a counter value. So my idea was to count pulses in a timeframe and then calculate flow from the K-factor of flowmeter. K-factor is how much flow/puls from flowmeter.

So my question is.
If I like to know the flow at any time, then it would be probelematic to count pulses in a time frame because then I need to wait until time is finish. Like if I count pulses in 1 minute to get flow/minute. I could ofcourse use a smal time like 50ms. But I have the feeling that this is not the best approach.

So what is the best way?

Best Regards
Hans

I think you need counter totalizer depends on PLC type.
It counts pulses/sec.

hapetter said:

Hi,

I have a flowmeter and an highspeed counter interface card.

I like to calculate the flow (ex. litre/min) from a counter value. So my idea was to count pulses in a timeframe and then calculate flow from the K-factor of flowmeter. K-factor is how much flow/puls from flowmeter.

So my question is.
If I like to know the flow at any time, then it would be probelematic to count pulses in a time frame because then I need to wait until time is finish. Like if I count pulses in 1 minute to get flow/minute. I could ofcourse use a smal time like 50ms. But I have the feeling that this is not the best approach.

So what is the best way?

Best Regards
Hans

Click to expand...

Many Flow Meters have a Pulse Output and a 4-20 mA Output. Is that the case with your Flow Meter? You can use the Pulse Count to display Flow Rate, you will probably not be able to use it for Control, the update is to slow in my experience.

However, the High Speed Counter Card may have built in Functions that you might be able to use, i.e. Frequency that would make it easier.

What Brand and Model of PLC and Counter Card are you using?

Stu...

If your card has a frequency function that is the way to go. Otherwise use a timer and counter to get pulses over a period of time, with the time depending on the speed of the pulse.

Some high speed counter cards offer a rate signal standard. If your's does, easy solution.

However, there is a general solution. You have already identified the method and the problems, I'll restate them to make it clear.

Count pulses over a relatively long time period. Problem: updates are only at the end of each period, too slow.

Count pulses over a relatively short time period. Problem: Output is noisy and erratic.

The solution is to combine the two methods.
Count pulses on a relatively short time period and place the results in a circular array. Calculate the flowrate based on the sum of the entire array. You get fast updates and a stable reading.