Watlow EZ-ZONE
®
PMI Controller • 218 • Chapter 10 Applications
Example 3: Square Root
Requirements:
One analog input and the enhanced software option are required and at least one output adjusts
the controlled part of the process.
Overview:
Calculates the square root value of the sensor connected to Analog Input 1.
When function is set for Square Root, the PV Function output equals square root value of Source
A. Control loop 1 will control Analog Input 1 to Set Point 1.
Example 4: Ratio
Requirements:
Two analog inputs and the enhanced software option are required and at least one output adjusts
the controlled part of the process.
Overview:
The Ratio feature allows control of one process as a ratio of another process. This is especially
useful in applications that mix two materials, whether steam, paint or food ingredients. Analog
Input 1 monitors the controlled part of the process. Analog Input 2 of the controller measures the
part of the process that is either uncontrolled or controlled by another device. The part of the
process controlled will be maintained at a level equal to the quantity measured at input 2 multi-
plied by the ratio term set by the user as Set Point 1. When function is set for Ratio, the PV Func-
tion output equals Source A as a ratio to Source B. Control loop 1 will control Analog Input 1 to Set
Point 1.
Applications of ratio control:
• Blending two or more flows to produce a
mixture with specified composition.
• Blending two or more flows to produce a
mixture with specified physical proper-
ties.
• Maintaining correct air and fuel mixture
to combustion.
Set Point 1
Function
Filter
Source A
Source A
Heat Power
Cool Power
0 to 100%
0 to 100%
Output
Heat
Cool
Output n
Output n
Analog Input 1
Control Loop 1
PV Function
controlled flow
of pigment
flow
transmitter
motorized
valve
Mixing Tank
flow
transmitter
mixed paint
uncontrolled
flow of
unmixed paint
®
Input 2
Input 1 Output 1
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