How would one come up with an average flow from the live GPM from the flow meter? I have the SCP set up and can watch the live GPM but I have fluid going through a filter and when the average flow drops below a set point I would like to activate a filter backwash cleaning cycle. Thanks
series of math instructions to come up with avg flow
- Thread starter Snap25
- Start date
I do not have a pressure sensor.. But I see what you are getting at.
Bit_Bucket_07
Member
As current within an electrical circuit obeys Ohm's law, so does liquid flow within piping obey Poiseuille's law.
inlet flow = outlet flow
Bit_Bucket_07
Member
You should better define your objective. "Average" flow can mean different things. There are multiple possibilities for deriving a running average, or for damping an input signal, which appears to be what you are seeking to accomplish. One method is to sum a fixed number of samples of the instantaneous flow rate and then divide that value by the number of samples taken.
I would like an average flow when the fluid is going into a freshly clean filter in the filter chamber so I can set a low flow setpoint to stop the filteeing to do a filter sleeve cleanse and resetting the ave flow figure. Then resume the filtering and doing another avg flow calculation.
Tom Jenkins
Lifetime Supporting Member
Use a timer to calculate a new average at the desired interval, and when the timer times out:
multiply the current average by the number of samples
add the current flow rate to the product
add one to the number of samples
divide the product by the new number of samples
the result is the new average
Use a second timer to terminate the calculation after the desired time has elapsed and zero the average and number of samples.
multiply the current average by the number of samples
add the current flow rate to the product
add one to the number of samples
divide the product by the new number of samples
the result is the new average
Use a second timer to terminate the calculation after the desired time has elapsed and zero the average and number of samples.
Tom Jenkins
Lifetime Supporting Member
I'm not sure what you mean. It is "standard" math, though, nothing exotic.
New average = ((old average x old number of samples) + new sample) / new number of samples
It is done with simple four function capabilities. The only caution is you may need floating point to maintain accuracy and avoid overflows.
NetNathan
Lifetime Supporting Member
What PLC and software are you using?
There may be a function in SFC...
There may be a function in SFC...
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TConnolly
Lifetime Supporting Member
See this post for an example program for computing a running average. It should be a simple matter to convert it to flow. In ControlLogix you can simplify the example further with a FIFO and the AVE instruction.
On cooling tower filters we use a differential pressure switch to trigger a backwash. However, it turns out that the cycle is fairly periodic and predictable. The load on the filter is virtually constant, so we could just as well use a timer. I mention this because a DP switch or time based are options to consider.
On cooling tower filters we use a differential pressure switch to trigger a backwash. However, it turns out that the cycle is fairly periodic and predictable. The load on the filter is virtually constant, so we could just as well use a timer. I mention this because a DP switch or time based are options to consider.
Last edited:
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