3.3 Function description
Basic function
The electronic control component is used for variable
and constant volume flow control for the TROX VAV ter-
minal unit type TVE. Its functional units consist of a
dynamic (XM0) or static (XS0) differential pressure
transducer, the controller electronics and the actuator.
Closed control circuit
The control component operates in closed loop, i.e. to
measure – compare – control.
Fig. 3: Principle of operation
1
Differential pressure transducer
2
Actuator
3
Volume flow controller
4
Setpoint value via Modbus or analogue signal
5
Shaft with effective pressure channel
The determination of the current volume flow rate takes
place by measuring a differential pressure (effective
pressure) directly on the damper blade. The effective
pressure is forwarded through the damper blade shaft to
the differential pressure transducer (1) integrated in the
control component and converted here into a voltage
signal.
The volume flow rate actual value is thus the internal
control loop as well as an external use, e.g. central BMS
or master-slave sequential circuit, available either as an
analogue voltage signal 0 – 10 V DC / 2 – 10 V DC or
as digital Modbus information.
In regular operation, the integrated actuator (2) is con-
trolled by permanent evaluation of the offset (setpoint
value-actual) in the volume flow controller (3) that
adjusts the damper blade of the VAV terminal unit via
the axle mounting and thus regulates the volume flow
rate to the setpoint value.
Due to the factory adjustment, the maximum starting
value 10 V DC always corresponds to the nominal
volume flow rate (q
vnom
) indicated on the adjustment
sticker on the VAV terminal unit. The factory-set q
vmin
and q
vmax
values can also be found on the adjustment
sticker or the order code. The q
vmin
and q
vmax
values can
be set individually on the display.
Setpoint value control independent of the duct pres-
sure
Fig. 4: Pressure independent control characteristics
The controller detects and corrects changes of the duct
pressure that may occur, for example, due to volume
flow rate changes from other units. The Compact con-
troller thus operates independently of the duct pressure,
and pressure fluctuations cause no lasting changes to
the volume flow rate.
In order to prevent the volume flow control from
becoming unstable, the controller maintains a dead
band (hysteresis) within which the damper blade is not
moved. This dead band and the tolerances of the meas-
urement lead to a volume flow rate deviation Δq
v
in
accordance with the product data sheets of the VAV ter-
minal units. If the conditions specified in the product
data sheets (e.g., minimum differential pressure,
upstream conditions) are not met, the controller will no
longer function correctly or more significant system
deviations can be expected.
Diagnostic options
Status of the control component
Setting the control component,
the control component’ on page 28
.
Troubleshooting
Structure and functional description
Function description
Control component Compact XM0 • XS0 for VAV terminal unit TVE
11