Watlow PPC-2000 - Manual (Page 130)

Chapter 3: Operating with AnaWin 3 PPC-2000 User’s Guide
106 Watlow Anafaze Doc.# 30002-00 Rev 2.3
Figure 3.7 How the Secondary Channel’s Set
Point is Determined When the Primary
Channel Has Only a Heat Output
Setting up Cascade Control
To setup cascade control:
1. Set up the primary loop. See Cascade Control Example
below.
2. Set up control for the secondary loop as you would for a
standard closed-loop application. See Setting up Control
Channels on page 92.
3. On the secondary channel:
a. Select the primary channel’s output (Channel # Out) for
the Set Point Source setting.
b. Set the Min Set Point to the desired set point when the
primary channel’s output is at its minimum value.
c. Set the Max Set Point to the desired set point when the
primary channel’s output is at its maximum value.
Cascade Control Example
The temperature of a tank of water is controlled by a heater
near the bottom of the tank. Two thermocouples measure the
water temperature. One is placed near the heater and is
referred to as the outer TC. The other is placed in the center of
the tank and referred to as the inner TC. The desired
temperature of the water at the inner TC is 150°F.
The inner TC is connected to the first input on the Analog Input
module. Output 22 on the Processor module is used to drive a
solid state relay power control. Figure 3.8 on page 107
illustrates this application.
Set Point of the Secondary Channel
(Engineering Units)
Max Set Point
Min Set Point
0%
Primary Channel’s Heat Output (% of Full Scale)
100%
inner
outer
outer
outer