Analogue output depending on analogue input

Hi First post so please be gentle.
As part of our waste water treatment plant we use compressed air through a sparge to provide a supply of small bubbles in the DAF tank.
The flow of air is dependant on the waste water pump pressure and the compressed air supply to the sparge. we are monitoring the compressed air flow in litres per minute through the sparge via a SMC air flow meter which has a 4-20mA output.
We are finding we have to constantly adjust the air pressure to maintain a consistant flow ( approx 40l/min ).
I have purchased a electronic air pressure regulator which takes a analogue signal and controls the air pressure.
The plc closest to this setup is a Micrologix 1100 with analogue output/ input module.

Question is what would be the best way to program it so there is a setpoint ( 40 l/min ) then taking the analogue output from flowmeter ( approx 7mA ) and then control the analogue output to the vairable air regulator so a constant air volume is achieved.

Thanks
Wayne

IMO you NOT need to use PLC , use normal controller.

set the SP on controller and the controller the task.

If that's ALL you're doing, then I concur with osmanmom, find a closed-loop controller.

If that's not an option for you, then you'll want to implement a PID instruction in your PLC. Implementing that for the first time requires a lot of reading and I don't really have time to write the novel of information it would require.

That's why a standalone controller would make this a lot easier and faster. Someone already engineered the application for you, you just have to implement it. Here's something that might be up your alley: http://www.dwyer-inst.com/Product/Flow/MassFlowmetersandControllers/SeriesGFC

Thanks guys for the quick response.
Your right Ive worked out that a pid is too complex for what I need to do and did have trouble setting it up in the ML1100.
Ive reserected a bit of code I wrote to replace the control board in a large pressure cleaner and modified it to suit,
Ended up comparing incoming analogue to a setpoint then if it it was either higher or lower just subtracting or adding 1 to the setpoint of the analogue to the pressure regulator. used a timer cycling every 5 seconds to do the pulse.

Thanks

sparksy said:

Ended up comparing incoming analogue to a setpoint then if it it was either higher or lower just subtracting or adding 1 to the setpoint of the analogue to the pressure regulator. used a timer cycling every 5 seconds to do the pulse.

Thanks

Click to expand...

That's often called deadband control or floating control. I use it often for controlling aeration blowers and such. It is not only easier to program than ID, it is a lot more stable, a lot easier to tune, and a lot less sensitive to imprecise tuning!

mostly i saw in WWT they use motorize to control the bubble blower motor.