Watlow CLS200, Руководство пользователя

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CLS200 Series User’s Guide
Chapter 5: Enhanced Features
110
Setpoint Differential
Enter the value to add or subtract from the ratio loop setpoint calculation before using it as the
setpoint. This value is expressed in the same engineering units as the ratio loop’s process variable.
ALARM
02 RATIO CONTROL
SP DIFF? 0
Selectable values: -9999 to 9999 with the decimal placement determined by the DISP FORMA T
setting for the ratio loop.
Ratio Control Example: Diluting KOH
A chemical process requires a formula of two parts water (H
2
O) to one part potassium hydroxide
(KOH) to produce diluted potassium hydroxide. The desired flow of H
2
O is 10 gallons per second
(gps), so the KOH should flow at 5 gps. Separate pipes for each chemical feed a common pipe. The
flow rate of each feeder pipe is measured by a CLS200, with H
2
O flow as process variable 1 and
KOH flow as process variable 2. The outputs of loops 1 and 2 adjust motorized valves.
CLS200
Loop 1 PID Output
Loop 2 PID Output
Loop 1 Input
Process Variable
Loop 2 Input
Process Variable
Motorized Control Valve 2
Motorized
Control
Valve 1
Mixture Output
Water Input
KOH Input
Flow
Transducer
Loop 1: Water Flow Control Loop
Loop 2: KOH Flow Control Loop
Serial
DAC
Serial
DAC
Figure 5.8 — Application Using Ratio Control
To set up this application, you would do the following:
1. Adjust and tune loop 1 (H
2
O) for optimal performance before implementing the ratio setup.
2. Switch the controller to display loop 2 (KOH), and then enter the three-key sequence
( ENTER , then ALARM ACK , then CHNG SP ) and go to the first screen in Table 5.3 .
3. Follow the steps in Table 5.3 to configure ratio control.