I have to implement Penstock Opening and Closing according the flow rate.
I get the Flowrate from Transmitter and I will make decision it.How i can control opening of Penstock.
For Example if flowrate is 1000 open penstock 10%
if Flowrate is 2000 open penstock 20% and vice verse also.
I am beginner.I think I have to use PID but how?Is there any other way.
Thanks
Hi,
I work for a water company and we use this philosophy to control the flow across our sand filters. We don't use a PID loop.
We simply try to maintain a flow rate across the filter. For example:
FLOW SETPOINT = 100L/s (Litres a second)
ACTUAL FLOW = 90L/s
VALVE POSITION = 45%
In the above scenario, our control philosophy is to pulse the valve an open signal until it reaches flow setpoint.
In the ladder we have a "Greater Than" block which compares the set point to the actual flow, if it's greater it allows the rung to continue through a 1 second timed bit that switches every 5 seconds (ON for 1 second, off for 5). This pulses the valve open for 1 second every 5 seconds until the flow rate is achieved. This also the same for Less Than, but obviously closes the valve.
The actual position is NOT used by the PLC control. This is because the feedback pots in ROTORK valves tend to play up over time, causing the control of the valve to play up. This way, however, uses the flow meter to control, which is much more practical.
Hope this helps!
EDIT: Just thought I'd point out that we use a deadband for the setpoint against the actual flow, this is to help stop the valve from opening and closing continuously (although with this control method it's hard to avoid, flows tend to wander around)