JOHNSON CONTROLS
166
FORM 100.50-NOM12
ISSUE DATE: 04/02/2019
SECTION 8 – SERVICE
TABLE 56 -
DUCT PRESSURE TRANSDUCER
1.25" W.C.
SPAN
DIFFERENTIAL
INPUT PRESS
2.5" W.C.
SPAN
DIFFERENTIAL
INPUT PRESS
5.0" W.C.
SPAN
DIFFERENTIAL
INPUT PRESS
VOLTAGE
VDC
0.125
0.25
0.5
0.50
0.25
0.50
1.0
1.00
0.375
0.75
1.50
1.50
0.50
1.00
2.00
2.00
0.625
1.25
2.50
2.50
0.75
1.50
3.00
3.00
0.875
1.75
3.50
3.50
1.00
2.00
4.00
4.00
1.125
2.25
4.50
4.50
1.25
2.50
5.00
5.00
Building Pressure Transducer
The Building Pressure Transducer is located in the re-
turn air section of the unit. The purpose of the trans-
ducer is to sense and convert the static pressure in the
building to a 0 to 5VDC voltage. The DC voltage is
then sent to the IPU board and compared against the
building pressure active setpoint. The transducer is fac-
tory wired, but pneumatic tubing must be field supplied
and installed (refer to
).
The Building Pressure Transducer measures differen-
tial pressure in the building and atmospheric pressure.
When verifying transducer operation, the technician
can insert a tee into the pneumatic tubing and connect
a manometer to the tee to verify the pressure being ap-
plied to the transducer. Once this pressure is known, a
comparison can be made of the building pressure vs.
output VDC from the transducer. A practical and quick
check of this transducer can also be accomplished by
removing the pneumatic tubing lines from both the low
and high side connections on the transducer. Since both
of the inputs will now be exposed to the same pressure,
the differential pressure is zero, and the output 2.5VDC
Return Fan Pressure Transducer
If the unit is order with the Return Fan Option the unit
has a Return Fan Pressure Transducer. The transducer
is mounted in the return compartment and compares
the pressure in the return air compartment to atmo-
spheric pressure. The IPU board varies the speed of the
Return Fan in order to maintain the correct differential
pressure in the return compartment. When verifying
transducer operation, the technician can insert a tee
into the pneumatic tubing and connect a manometer to
the tee to verify the pressure being applied to the trans-
ducer. Once this pressure is known, a comparison can
be made of the return compartment pressure vs. output
VDC from the transducer. A practical and quick check
of this transducer can also be accomplished by remov-
ing the pneumatic tubing lines from both the low and
high side connections on the transducer. Since both of
the inputs will now be exposed to the same pressure,
the differential pressure is zero, and the output 2.5VDC
TABLE 57 -
BUILDING PRESSURE
TRANSDUCER OUTPUT
DIFFERENTIAL INPUT
PRESSURE - "W.C.
OUPTUT VOLTAGE - VDC
-0.50
0.00
-0.40
0.50
-0.30
1.00
-0.20
1.50
-0.10
2.00
0.00
2.50
0.10
3.00
0.20
3.50
0.30
4.00
0.40
4.50
0.50
5.00
TABLE 58 -
RETURN FAN PRESSURE
TRANSDUCER OUTPUT
DIFFERENTIAL INPUT
PRESSURE - "W.C.
OUPTUT VOLTAGE - VDC
-1.00
0.00
-0.80
0.50
-0.60
1.00
-0.40
1.50
-0.20
2.00
0.00
2.50
0.20
3.00
0.40
3.50
0.60
4.00
0.80
4.50
1.00
5.00
