User Manual

Siemens Building Technologies Application : 78 RWD32/78 – 04.2001
HVAC Products RWD32 2
The temperature sensor senses the room conditions and on a rise in temperature
the RWD32 via Q1, Q2 digital outputs modulates the three position cooling valve
as determined by cooling set point and proportional band settings.
The connection of a number of temperature controllers in series, the cooling Y2
output of the previous controller connected to the X2 input of the following
controller, together with the maximum priority function in each controller, results in
the highest call for cooling controlling the position of the chilled water valve.
Three position control has no feedback from the valve actuator to determine it’s
position, so the timing of the actuator must be known to the controller. During
commissioning the actuator timing must be entered. A common actuator timing
for small three position valve and damper actuators is 150 seconds from fully
open to fully closed, so this means that the controller modulates the actuator over
the Xp proportional band range for 150 seconds.
E.g. An Xp proportional band of 4º C and 150 second cycle time means that for
a 4º C change the controller will drive the actuator for 150 seconds.
A synchronous check on the position of the actuator is carried out on a regular
basis.
Cooling sequence
Load
Setpoint
Cooling
0%
100%
Q
2
Q
1
Xp
Valve
Opening
Actuator timing
L
S1
D1
N
BM
X1 X2MM
X1
M
G AC 24 V
Q12 Q14
RWD32
Q11
Q22 Q24
Q21
Q1 Q2
N1
TOOL
PC
G
(L) AC 230 V
N
Y1 Y2
N
GO
CCV
X2
From other
controllers
RWD32
N1 RWD32 controller
X1 Main temperature sensor
X2 Input from other controllers
S1 Time clock or switch
Q1 Opening contact for 240Vac 3 - position control valve
Q2 Closing contact for 240Vac 3 - position control valve
CCV 3 – position 240Vac chilled water control valve
PC Personal computer
Description of operation
Function diagram
Connection diagram