Example 7: wet bulb / dry bulb, Example 8: vaisala, Vaisala – Watlow EZ-ZONE PM Integrated Controller User Manual

Page 155: Wet bulb/dry bulb

Watlow EZ-ZONE

PM Integrated Controller

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152

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Chapter 10 Applications

Example 7: Wet Bulb / Dry Bulb

Requirements:
Two analog inputs and at least one output are required to adjust the controlled part of the processes.
Overview:
Wet Bulb/Dry Bulb is a configuration where a dry

bulb connected to Analog Input 1 measures tem-

perature on Analog Input 1. A wet bulb sensor that

is maintained with moisture has air moved over the

sensor. As moisture evaporates from the wet bulb, the

temperature drops. A wet bulb input on Analog In-

put 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 In-

put 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 hu-

midity. Control loop 1 will control Analog Input 1 to

Closed Loop Set Point 1. Control loop 2 will control

Analog Input 2 to Closed Loop Set Point 2.

Example 8: 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 supported with the Vaisala

configuration. Analog Input 1 is used to mea-

sure temperature and Analog Input 2 must be a

process input connected to a Vaisala sensor. The

controller provides temperature compensation

for the Vaisala sensor. The humidify and dehu-

midify 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 Vais-

ala, the PV Function output equals the calculat-

ed relative humidity compensated by the sensor

on Analog Input 1.

Wet Bulb/Dry Bulb

Closed Loop

Set P

oint

Closed Loop

Set P

oint

Function

Filt

Source A

Source B

Source A

Heat Power

Cool Power

0 to 100%

Output

Heat

Cool

Output n

Analog Input 1

Analog Input 2

Control Loop 2

Control Loop 1

PV Function

Temperature

Humidity

Vaisala

Closed Loop

Set P

oint

Closed Loop

Set P

oint

Function

Filt

Source A

Source B

Source A

Heat Power

Cool Power

0 to 100%

Output

Heat

Cool

Output n

Analog Input 1

Analog Input 2

Control Loop 2

Control Loop 1

PV Function

Temperature

Humidity