Originally Posted by
foreigneRS
his requirement seems quite clear to me
he wants to control the speed of a couple of 240V motors with a PID loop so that they maintain a speed necessary to achieve an output on some kind of 0-5V sensor
And its obvious to me but its nice to know the application details.
One problem you have is controlling the speed of AC motors requires a device called a "variable speed drive" or VSD as its known.
These are not cheap !!
Motor speed of AC motors is dictated by the AC frequency and not the voltage given to it !
You cant use a variable resistor and if you could it would be BIG !
There are some cheap single AC phase drives out there but I dont use them so cant recomend any. (I use 3 phase mainly ! )
This VSD will take an input signal as a voltage or current.
This will either be a 0-10 volts input or 4-20 milliamp signal (industry standards)
Some exampes here....
http://www.abb.com/product/seitp322/...b002d1ad2.aspx
As for a controller, thats easy, there are many such PID controllers available from about £50 upwards.
These output standard signals as described above and take a multitude of inputs.
Some VSD's contain built in PID controllers so may be more of a compact solution.
Hope that gves you an insight