Watlow MLS - Manual (Page 111)

Tuning and Control
MLS User’s Guide 99
Tuning and Control
Introduction
This chapter explains PID control and supplies some starting PID values
and tuning instructions, so that you can use control parameters
appropriate for your system. If you would like more information on PID
control, consult the ANAFAZE Practical Guide to PID.
The control mode dictates how the controller responds to an input
signal. The control mode is different from the type of control output
signal (like analog or pulsed DC voltage). There are several control
modes available: On/Off, Proportional (P), Proportional and Integral
(PI), Proportional with Derivative, and Proportional with Integral and
Derivative (PID). P, PI, or PID control are necessary when process
variable (PV) cycling is unacceptable or if the process or setpoint (SP) is
variable.
NOTE
For any of these control modes to function, the
loop must be in Automatic mode.
Control Modes
The next sections explain the different modes you can use to control a
loop.
On/Off Control
On/Off control is the simplest way to control a process; a controller
using On/Off control turns an output on or off when the process variable
reaches a certain limit above or below the desired setpoint. You can
adjust this limit, since ANAFAZE’s controllers use an adjustable spread.
For example, if your setpoint is 1000
º F, and your limit (spread) is 20
º F, the output switches On when the process variable goes below 980 º F
and Off when the process goes above 1000 º F.