Watlow PM PLUS™ 6
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Chapter 9: Applications
Example 6: Wet Bulb / Dry Bulb
Requirements: Two analog inputs and at least one output are required to adjust the controlled part of the pro-
cesses.
Overview:
Wet Bulb/Dry Bulb is a configuration where a dry bulb
connected to Analog Input 1 measures temperature
on Analog Input 1. A wet bulb sensor that is main-
tained with moisture has air moved over the sen-
sor. As moisture evaporates from the wet bulb, the
temperature drops. A wet bulb input on Analog Input
2, in combination with the dry bulb temperature,
senses relative humidity. The controller calculates the
temperature difference between the two sensors to
determine percent relative humidity. The humidify and
dehumidify outputs are disabled when Analog Input 1
temperature falls below 32 F/0 C, or goes above 212
F/100 C. When function is set for Wet Bulb/Dry Bulb,
the PV Function output equals calculated humidity.
Control loop 1 will control Analog Input 1 to Set Point
1. Control loop 2 will control Analog Input 2 to Set
Point 2.
Example 7: Vaisala
Requirements: Two analog inputs and the enhanced software option are required and at least two outputs
adjusts the controlled temperature and humidity processes.
Overview: Vaisala Model HMM-30C Solid-
state Relative Humidity Sensor is support-
ed with the Vaisala configuration. Analog
Input 1 is used to measure temperature
and Analog Input 2 must be a process
input connected to a Vaisala sensor. The
controller provides temperature compen-
sation for the Vaisala sensor. The humidify
and dehumidify outputs are disabled when
Analog Input 1 temperature falls below
-40 F/- 40 C, or goes above 320 F/160 C.
When function is set for Vaisala, the PV
Function output equals the calculated rela-
tive humidity compensated by the sensor
on Analog Input 1.
Vaisala
Set Point 2
Set Point 1
Function
Filter
Source A
Source A
Source B
Source A
Heat Power
Heat Power
Cool Power
Cool Power
0 to 100%
0 to 100%
0 to 100%
0 to 100%
Output
Heat
Heat
Cool
Cool
Output n
Output n
Output n
Output n
Analog Input 1
Analog Input 2
Control Loop 2
Control Loop 1
PV Function
Temperature
Humidity
Wet Bulb/Dry Bulb
Set Point 2
Set Point 1
Function
Filter
Source A
Source A
Source B
Source A
Heat Power
Heat Power
Cool Power
Cool Power
0 to 100%
0 to 100%
0 to 100%
0 to 100%
Output
Heat
Heat
Cool
Cool
Output n
Output n
Output n
Output n
Analog Input 1
Analog Input 2
Control Loop 2
Control Loop 1
PV Function
Temperature
Humidity
