pulses per second to flow rate output in cubic meter per hour

shujauddin

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S
Join Date
Oct 2012
Location
hyderabad
Posts
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Hi,

I am using GE Fanuc PLC to calculate the Flow rate in cubic meter per hour from pulses output. i.e. Pulses per second. But the method i used is suitable if i have pulses per volume defined. But for (LF Meter) through which i am measuring Flow rate, that is not defined. Hence any other methods which could give me precise flow rate value in Cubic meter per hour.
 
What output your meter is giving you may be helpful. Specific meter you are using even more helpful...

Best guess from what you have given, is that if you have a pulse output meter that is not indicative of a volume, then it is likely equal to a speed. If you know the speed the media is traveling, then you need to find the area of the container it is passing through. Meters Squared * Meters/sec = Cubic Meters/sec

Precision will be based on how careful you are with your area calculations, and how laminar the flow is.
 
Take the number of pulses you get in (1 minute X 60 )X cubic meters in each pulse. If you don't know how many cubic meters per pulse you will need to calculate this first based on what you do know.
Or maybe I don't understand the question?
 
Last edited:
The formula i used for this calculation is - (pulses/ sec* 3600)/max no. of pulses per cubic meter. The pulse/sec output i am getting by configuring my PLC in HSC mode. The number of max. pulses per cubic meter is defined per meter. The meter i am using for this operation is Romet Meters. Basically i am performing the Proving Process. So for some meter the max. number of pulses per cubic meter is not defined. So there the Problem arises and for some LF Meters we don't even get pulses/ sec from Register. So just by using the output pulses from Meter i need to calculate the Flow rate. Hope i am quite clear with my Query. Need your inputs on this. :)
 
If I'm understanding correctly, it sounds like two problems.

1. Scale will change based on meter used - You may need an HMI or some way to update the scale based on the meter.

2. Some Low Flow meters do not give you a pulse every second, or enough pulses to preform an accurate measurement. In this case you may need to change your time base.
 
With out changing my Time Base can i any how calculate the Flow rate. For some Low Frequency Flow meters the pulses are not so frequent so in order to have proper flow rate measurement i want to make my final calculation independent of Time Base. Can you suggest any method which will be useful for such calculations
 
Basically you either need to determine if a longer time base is suitable for all application (Perhaps measure volume over 5 sec instead of 1) or make an adaptive time base. Number of seconds vs a minimum change. With this you will also need a timeout, after which you determine there is no change, and move a 0 into your flow. also you will need to modify the 3600 in your equation based on the amount of time your sample is.
 
i have tried working out with program for calculating TD between two pulses but it is true for first 2 pulses but after that its not taking into consider pulse between 2 & 3 and same continues. it is considering pulses 1 & 2, 3 & 4, 5 & 6. But it is not considering TD between the pulses 2 & 3, 4 & 5 and so on. The flow rate value what i am getting is with gap of one Pulse? Can any one help me with this ?
 
Last edited:
shujauddin said:
i have tried working out with program for calculating TD between two pulses but it is true for first 2 pulses but after that its not taking into consider pulse between 2 & 3 and same continues. it is considering pulses 1 & 2, 3 & 4, 5 & 6. But it is not considering TD between the pulses 2 & 3, 4 & 5 and so on. The flow rate value what i am getting is with gap of one Pulse? Can any one help me with this ?
Click to expand...


You mentioned using a HSC which means that you are recording total volume and calculating flow. I believe the normal means for what you are trying to do is:

  1. Setup a timer (interrupt is better) for 1 sec or whatever time you would like to update at.
  2. Subtract Current HSC value from Previous Value to find difference in volume
  3. apply scale and multiplier values for Engineering units and time (ie 1 pulse = X M^3... * 3600 for hours)
  4. Move current HSC value into previous
This is the Pulse/Time Method... For Low Flow conditions, you'll also see Time/Pulse used. As Jesper said, a search will provide many discussions.
 

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