Differential Control; Ratio Control; Duplex Control - Watlow EZ-ZONE PM User Manual

Differential Control

The PM (PM8/9) can be configured for Differential
Control with enhanced firmware. After configuring
the appropriate inputs and their associated internal
functions Differential Control allows the PM to drive
an output based on the difference between those ana-
log inputs.

Ratio Control

The PM (PM8/9) can be configured for Ratio control
with enhanced firmware, especially useful in applica-
tions that mix materials. Ratio control is commonly
used to ensure that two or more flows are kept at the
same ratio even if the flows are changing.
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 properties.
• Maintaining correct air and fuel mixture to com-
bustion.

Duplex Control

Certain systems require that a single process output
control both heating and cooling outputs. A PM con-
trol with a process output can function as two sepa-
rate outputs. With a 4 to 20mA output the heating
output, for instance, will operate from 12 to 20mA (0
to +100%) and the cooling outputs will operate from
12 to 4mA (0 to -100%). In some cases this type of
output is required by the device, such as a three-way
valve that opens one way with a 12 to 20mA signal
and opens the other way with a 4 to 12mA signal.
This feature reduces the overall system cost by using
a single output to act as two outputs.
Note:
See Chapter 10 for application examples.
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Wat lo w EZ-ZO NE PM In t eg r a te d Co n tr o lle r
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Input 1
Output 1
Input 2
Input 1 Output 1
®
Input 2
controlled flow
of pigment
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Input 1 Output 1
1 1 0
• •
flow
transmitter
Mixing Tank
motorized
valve
Fluid S a mple Cont a ine r
hot water
cold water
Chapter 9 Fe a ture s
mixed paint
flow
transmitter
uncontrolled
flow of
unmixed paint
temperature
transmitter