implementing an open loop controller

[Marwan]

I have finished designing a Closed loop temperature controller. Using labview I designed a VI where the user monitor and control the loop settings (i.e., PID/OnOFF, PID settings, setpoint, process variable….etc).

Now I have been asked to include an open loop control in the VI. Now, I know in open loop the controller (which is PWM duty cycle 0-100% in my design) is manually controlled. My question is, is that mean to include a PWM control in the vi so the user can set it in the range of 0-100% or to use the setpoint controller to control the temperature? If its to be controled by the setpoint how can you implement that?

[Sima]

Hi Marwan, it really depends on what you're trying to achieve in open loop. Here are my questions for you:

• Do you want the user to be able to manually tune the raw signal (i.e. the PWM signal, in your case) until the user decides the desired reading is achieved?
• If the user did enter the setpoint, do you not care if the setpoint is not actually achieved?

Since this is open loop, there is of course, no guarantee that the setpoint will be reached with an open loop command. So, whether the exercise is simply to send an open loop PWM signal directly, or to interpret that signal from the setpoint, depends on what you really want to do.

By the way, can you explain more about your system? What (physically) are you controlling the temperature with? And why PWM? etc. Maybe also a brief description on how you did the closed loop part?