I want to control a motor (pump) speed via vfd in such a way that when temperature of the water increases the pump speed also increased and when temperature of the water decreases the speed of the motor (pump) also decreased ..... can we used external PID control with a VFD OR use a VFD having a PID control option and then tune up that PID control ?

It has to implement to maintain the temperature of water to a certain range

To control the cooling system as i stated above , what things / parameter should i calculate and measure first ?

i have ABB ACS 550 VFD which has a in built PID function , so how to tune up its PID ?
Do i need of a sensor i.e Pt 100 and a current signal converter for this setup ?

Hai munzir,
Most of the vfds are comes with built in PID settings, Use a temperature sensor as the analog input, Which we want to connect in VFD For control the speed of motor, . Parameters are motor name plate specifications and P,I And D values for the PID.
If you have any more doubts just replay to me.........

How ever with PT100 I do agree you do require signal conditioner unless and until the VFD you are employing does have a inbuilt signal conditioner. Please check thru the capabilities of the drive expected to be employed.

Yes Muralidhar sir, i mean analog signal need to connect for vary the speed, like 4 -20 ma corresponding to temperature.

First measure the temperature using RTD or thermocouple. Use a transmitter to convert the signal into a standard 4-20 mA signal. Use this 4-20 mA signal as an input to the PID of your VVF. The output of the PID should be the speed command for the VVF. Now you have to tune the PID slightly so that you can get the desired change in speed for the desired change in temperature

Sumesh p K :

What would be the P , I & D values for this process ?

thanks

Abhinav Sharma :

To tune the PID slightly so that i could get the desired change in speed for the desired change in temperature , what parameters should i change slightly ?

And also clarify me is it trial and error base procedure ?

Thanks awfully

There're software tools available for PID tuning but I dare say it's a trial error to some extent. You need to tune following parameters: Kp(propotional gain) and Ti(Integral time). As a guideline you may follow the procedure below:
1. Give a step change of eg 5% to the setpoint and observe the actual value if it reacts too slow then increase Kp or vice-versa.
2. With Kp alone error between setpoint and actual will never be zero, if it's too slow to remove the offset, then decrease Ti or other way round.

Make few step response to make sure tuning is good. While making tuning keep the process as much stable as possible.

Please note PID tuning is pretty subjective thing, if you will google you can find handful of articles explaining it.

Hope this helps.

Nitin Kakkar :

Would you mention those handy articles here ?

thanks indeed