Watlow Series 998 - Manual (Page 31)

WATLOW Series 998 User’s Manual 4.3 Setup Menus, Chapter 4
Setup-Input
Temperature and Relative Humidity
When the controller will be used to measure temperature and relative
humidity, channel A is designated as the temperature channel and chan-
nel B is the humidity channel. Any sensor type may be used for either
channel A or B. This includes thermocouples, RTDs or process inputs that
have been properly scaled to represent a temperature. Below are the three
methods for measuring relative humidity with the Series 998.
Wet Bulb/Dry Bulb In this configuration, a dry bulb connected to input 1
measures temperature on channel A. A wet bulb input on input 2, in com-
bination with the dry bulb temperature, senses relative humidity on chan-
nel B. The Series 998 calculates the temperature difference between the
two bulbs to determine percent relative humidity. With a wet bulb/dry
bulb configuration, the Input 2 Linearization prompt [Lin2] must be set
to [`Wb].
The humidify and dehumidify outputs (outputs 1B and 2B) are disabled
when the channel A temperature falls below 32˚F/0˚C, or goes above
212˚F/100˚C. The relative humidity process display in the Display Loop
will display the error code [E2`2] for a low temperature error and [E2`3] if
the temperature is above the range high.
Vaisala Model HMM-30C Solid-state Relative Humidity Sensor With
the Vaisala configuration, channel A is used to measure temperature and
channel B must be a process input with the Input 2 Linearization prompt
[Lin2] set to [`30C]. The Series 998 provides temperature compensation
for the Vaisala sensor. The humidify and dehumidify outputs (outputs 1B
and 2B) are disabled when the channel A temperature falls below -40˚F/-
40˚C, or goes above 320˚F/160˚C. The relative humidity process display in
the Display Loop will display the error code [E2`2] for a low temperature
error and [E2`3] if the temperature is above the range high.
NOTE:
See Input 2
Linearization
[Lin2] in this chap-
ter.