motor speed control

[arambler]

Hey I am new use of TriLOgi...   I am interested to design a motor speed control either AC or DC but after long efforts I can't understand how can I make a ladder logic for it.  

Please help me.  

I'll very thankful for any help

[support]

It depend on what you mean by speed control. Most AC motor speed is controlled by Frequency Inverter and not a job for the PLC. For the simplest form of  (open-loop) speed control you can use the PWM output of the PLC to apply variable voltage to the motor.  You can close the loop by monitoring the speed of the motor using the PLC's Pulse measuremnt inputs (PM0 and PM1) and perform necessary correction to the PWM output.

More sophiscated or high horse power DCmotor have their own dedicated speed controller and the PLC can interact with them using either analog output or via RS232/RS485 communication.

[arambler]

Thnks for a quick reply
please guide me
for a ladder I am actually intrested in DC speed control how can i start developing ladder for it using Trilogi

[philipjoseph]

Do you have any DC or AC drive to control the speed?
What are the input that the drive have (DI,DO,Comunication-RS232,RS485)?

If you have a drive you can start thinking about control the speed of a motor.

[Quang]

Hey I am new use of TriLOgi...   I am interested to design a motor speed control either AC or DC but after long efforts I can't understand how can I make a ladder logic for it.  

Please help me.  

I'll very thankful for any help

[support]

To give you an example, you can use TBASIC  SETPWM command to setup Pulse Width modulated output to connect to a small motor

  SETPWM 1,5000, 2000

The above setup the output to 50% duty cycle, by varying the duty cycle you can change the average amount of DC voltage applied to the motor and hence the speed can change.

To close the loop,  you can use the PMON command to setup a pulse measurement function to measure incoming pulse frequency or period on Pulse Measurement channel #1

   PMON 1  ' execute this in a 1st.Scan custom function

You will then use a 0.05s clock pulse to trigger another custom function, which will measure the PULSEFREQUENCY to calculate the actual speed of the motor. If it is below the desired speed, then you will have to increase the duty cycle to PWM. If it is above, then you decrease the PWM duty cycle. This is a simple but crude method. A more elegant method is to apply the PID  method to control the motor speed. But you need some PID control background to understand how to scale the input and output for PID control.

However, please note that you can't simulate this program because it is difficult to simulate  the incoming pulse stream

[meiya777]

It depend on what you mean by speed control. Most AC motor speed is controlled by Frequency Inverter and not a job for the PLC.

Well, it's not true. Am new to PLC and intend to control AC motor by Inverter. The inverter can be controlled by various kinds of Analog Input such as Potentiometer, or Voltage Input (0..10vdc) or Current Input (4..20mA). Or if you want, they can controlled by Digital Input, even direct PLC signal power. I use  Fuji Frenic 5000G11S inverter.

[support]

That's what we meant. It is the Inverter's job to control the speed of the motor. The PLC on its own cannot directly control the speed of the AC motor.  However, most inverters allow some kind of external control such as analog inputs or serial port inputs. If the inverter provides such interface then you can use the PLC to control the inverter's settings.