Watlow 12LS Controller - Manual (Page 92)

5-1
5.0 PID CONTROL
The information provided in this manual is provided to get the system up and running with a
minimum of effort. For further details of the use and tuning of PID control see the ANAFAZE
Practical Guide for Process Control.
5.1 CONTROL MODES
The control mode is the form of control function. In the 12LS the choices are: on/off,
proportional [P], proportional and integral [PI], and proportional with integral and derivative
[PID]. The control mode should not be confused with with the type of control output signal: for
example pulsed DC voltage or analog output.
5.1.1 REVERSE-DIRECT ACTION
The ACTION of the control OUTPUT with RESPECT to the PV is known as REVERSE
ACTION, if the OUTPUT INCREASES as the PV DECREASES. If the OUTPUT INCREASES
as the PV INCREASES, then it is known as DIRECT ACTION.
Heating applications normally uses REVERSE ACTION and cooling applications normally will
use DIRECT ACTION. The selection may also be dependent upon the application of two
competing mediums of energy such as in a HEAT/COOL or TEMPERATURE/HUMIDITY
applications.
5.1.2 HEAT/COOL DUAL OUTPUTS
Dual outputs are provided standard in the ANAFAZE 12LS. Each loop control mode, and output
signal type, and a spread between the setpoints. The deadband adjustment is not normally
possible in many controllers. Three-Position or Two-Position floating control can be
implemented by selecting the proper deadband between setpoints of the heating and cooling
loops.
5.1.3 CONTROL OUTPUTS
The 12LS provides a output signal of 5 Vdc for use as PID control outputs. An analog output
signal of 0 to 5 Vdc or 4-20 mAdc is available using a external module called a DAC from
ANAFAZE.
5.1.4 DIGITAL OUTPUT
PID Digital outputs normally control the process using relays. Three types of control are used:
ON/OFF, TIME PROPORTIONING, and DZC.