Specifications

77
19.0 AC400 PID SETPOINT CONTROL
PID Setpoint Control allows the AC400 to maintain a process setpoint, such as PSI or CFM,
without using an external controller. When PID is activated, the AC400 will operate in a
closed-loop fashion, automatically adjusting the motor speed to maintain the setpoint.
PID setpoint control requires feedback from the process in order to compare the process
variable “value” to the setpoint. The difference between the process variable “value” and the
setpoint is called the error. The AC400 will increase or decrease the motor speed in an
attempt to minimize the error. By constantly adjusting the motor speed, the PID control will
drive the process toward the setpoint. Refer to the PID block diagram below:
19.1 FEEDBACK DEVICES
A transducer or transmitter is required to monitor the process variable and provide feedback
to the PID unit in order to compare the process variable feedback to the setpoint. A
transducer outputs a signal corresponding to a fixed range of the process variable. A
transmitter provides offset and gain adjustments to allow the output signal to be adjusted to
correspond to different ranges of the process variable. Typical output signals for transducers
and transmitters are: 0-5 VDC, 0-10 VDC, or 4-20 mA. The feedback device must be
externally powered, as the drive does not have a power supply for such devices. Program
Parameter 74 - PID FB (PID FEEDBACK SOURCE) for the appropriate terminal (TB-5A or
TB-5B), and connect the feedback device as described below:
POT The positive signal wire (wiper) is connected to TB-5A, and the “high” lead is
connected to TB-6.
0-5, 0-10 VDC Connect the positive signal wire to TB-5A.
4-20 mA Connect the positive signal wire to TB-5B.
The common, or negative signal wire, is connected to TB-2 (circuit common).