15
VAPOR-LOGIC
®
VERSION 6 INSTALLATION AND OPERATION MANUAL
Example: 12 mA – 4 mA
Calculation of transmitter % RH
INSTALLATION
x 100%
x 100% = 50% RH
Step 1 – Field wiring: Control input signals
MODULATING DEMAND SIGNAL CONTROL
With modulating demand signal control, a modulating humidistat
or a building automation system sends a signal to the Vapor-logic
controller, which then sends a signal to the humidifier to produce
a directly proportional steam output . For example, if a humidistat
operating between 4 mA and 20 mA sends a 4 mA signal,
the humidifier produces no output; a 12 mA signal causes the
humidifier to run at 50% of capacity; and a 20 mA signal causes
the humidifier to run at 100% capacity .
With a humidistat provided by DriSteem producing this signal, the
humidity set point is set at the humidistat . The display then is used
for maintaining and troubleshooting the humidification system,
with humidifier control stemming from the humidistat itself . With a
building automation system (BAS) providing the signal, the humidity
set point is established by the BAS, and the humidifier responds to
the BAS commands .
16 mA
TRANSMITTER CONTROL
With transmitter control, the Vapor-logic board receives a signal
that corresponds to the actual humidity level measured in the space
being controlled . (With a transmitter provided by DriSteem, the
signal is 4 to 20 mA, which corresponds to 0 to 100% RH) . The
Vapor-logic controller employs an internal PID loop that uses this
humidity measurement along with a user-defined humidity set point
to calculate a demand level . This demand level is the level at which
the humidifier will run . See “PID tuning” on Page 49 .
% RH =
(mA reading) – 4 mA
16 mA
