So my company has chosen to install VFDs in place of some vortex vanes. The vortex dampers were being controlled by floating type control. (Open Damper, Close Damper, and Hold Position) Someone in my office sold the job to reuse the floating type control as inputs to speed up and slow down the VFD and hold its speed. I really don't like this particular control sequence, and I have never seen a VFD controlled in this manner.
The controls engineer has instructed me to write a custom program in Tridium that determines the VFD percentage based off of time. So I am assuming that if I have a 60 second acceleration/deceleration time on the VFD. I can write some logic stating the number of seconds the speed up or slow down output is active. I would count up during a speed up command, and count down during a slow down command. I would hold the count when in the hold command. I am trying to get my head around doing this sequence. I feel that this particular way of doing this can become very inaccurate at times. I know I have to incorporate a min/max so that the count doesn't go over 100 or below 0. I am also planning on using a PID to output the count. I am wondering if anyone has written anything similar to this before? If so can you give me some pointers on how I need to approach something like this. I told the office it would of been a lot easier if they would have just set up a analog output on the AHU controller, but they are XL5000 controllers and I guess our company doesn't have the CARE tool. So here I am with this situation.
Thanks for any advice you may have.