VAV-SVX03A-EN
11
The following tools are required to
properly adjust and calibrate the
electronic controls:
Digital voltmeter
0-2 in. wg magnehelic gage (or inclined
manometer)
Tubing and fitting to connect gage to
flow ring tees (5/32" and 1/4" tubing).
Mechanical tools (screwdriver,
pliers, etc.)
Calibration
Null Voltage
The tolerance for the output voltage of
the transducer with zero delta P signal
from the flow ring is referred to as the
null voltage of the transducer. The
transducer has three wires leading
from it to the control board. The wires
include a common (green wire), an
input (red wire), and an output (black
wire). The input (supply) voltage to the
transducer is 5 volts (+ .5). The accept-
able voltage range of the output voltage
with zero flow (between black and
green) can range from .100 volts to .400
volts. To allow the controllers to
coordinate with the transducer voltage,
internal calibration is necessary. To
accomplish this, potentiometer R8 (zero
flow adjustment) is used. The flow
voltage signal should be 4.8 volts at test
points #1 and #3 of the test point
terminals (next to R8) with zero delta P
applied. R8 is used to adjust the flow
voltage to 4.8 volts when zero delta P is
applied to the transducer. In this
manner, variability of the null point of
the transducer is compensated for. The
importance of this becomes evident
when minimum and maximum flows
are discussed.
PROCEDURE FOR
MAXIMUM AND MINIMUM
CALIBRATION
Initialization
1. Monitor thermostat voltage and check
it by rotating the thermostat to full
heating and full cooling.
a. Connect a voltmeter to TB1-4 (+)
and TB1-3 (-).
b. Rotate the thermostat fully
clockwise (full heating). Observe
the voltage. It should be less
than or equal to 5.4 volts DC.
c. Rotate the thermostat fully
counter-clockwise (full cooling);
voltage should go up to 6.3 volts
DC or greater.
2. Set the min/max pots as follows:
a. Rotate the max pot (R67) full
clockwise.
b. Rotate min A (R68) full counter-
clockwise
c. Rotate min B (R69) full counter-
clockwise
3. With both of the transducer ports open
to ambient (0 delta P), read the output
voltage at TP4. (Ground is either TP3,
TB1-2, or TB1-3.) The value of the null
transducer voltage output must be
between 0.1 and 0.4 volts DC.
Nominal is .250 volts DC.
4. Monitor TP1 (+) voltage (zero flow
adjustment) and adjust R8 until 4.8
volts DC + .010 volts is read at TP1.
Set Maximum Flow
Set the thermostat knob to the full-cool
position (fully counter-clockwise)
thermostat voltage should go over 6.2V
DC. Connect a pressure gage teed into
the high- and low-port flow ring of the
transducer and input the maximum
delta P. Refer to the flow vs. delta P chart
on the unit to obtain the proper delta P
signal desired. Adjust the max pot (R67)
so that both the amber and green lights
are out, this indicates that equilibrium
has been established with the delta P
input to the transducer.
Hazardous Voltage!
Certain tests or calibration procedures
described in this section may involve
working in close proximity to live
electrical terminals. Only qualified and
licensed electrician or other properly
trained in electrical safety when
working with live voltage should
perform these procedures. Failure to
follow all electrical safety precautions
when exposed to live terminal could
result in death or serious injury.
WARNING
WARNING
Transducer Operation
This section discusses how airflow
through the damper is transformed into
a voltage signal that can be used by the
controller. The first transition from flow
to voltage occurs at the Trane flow ring,
where a delta P signal is generated as a
function of airflow through the unit. The
delta P signal consists of a high-
pressure signal from a total-pressure
tap of the airflow ring and a low-
pressure signal from the wake-
pressure side of the flow ring.
The transducer converts the pressure
differential signal to an output voltage.
The output of the transducer with no
flow or zero delta P is .250 volts DC
(+ .100). As flow increases, the delta P
signal increases; therefore, the output
voltage of the transducer increases. The
gain of the transducer is 0.75 volts per
inch of delta P.
