113
JOHNSON CONTROLS
FORM 145.05-NOM1 (708)
ANALOG INPUTS
Temperature Sensors
The temperature sensors are all 10K Type II thermistors.
The relationship between the temperature and the
resistance is contained in Table 21. The following
analog outputs are of this type:
• Supply Air Temperature
• Return Air Temperature
• Mixed Air Temperature
• Slab Temperature
• In Water Temperature
• Out Water Temperature
• Outdoor Air Temperature
• Coil Leaving Temperature.
TABLE 21 – TEMPERATURE SENSOR
RESISTANCE
° F
RESISTANCE
(OHMS)
° F
RESISTANCE
(OHMS)
-25 196,300 60 15,310
-20 165,100 65 13,480
-15 139,300 70 11,880
-10 118,000 75 10,500
-5 100,200 80 9,298
0 85,350 85 8,250
5 72,910 90 7,331
10 62,480 95 6,532
15 53,640 100 5,826
20 46,230 105 5,209
25 39,910 110 4,663
30 34,560 115 4,182
35 30,000 120 3,757
40 26,100 125 3,381
45 27,760 130 3,047
50 19,900 135 2,750
55 17,440 140 2,486
Duct Pressure Transducer
A duct pressure transducer is located in a control box
to the left hand side of the main control enclosure on
two compressor units and to the right hand side of the
main control enclosure on 4 compressor units. There
may be one or two transducers depending on how the
unit was ordered. The purpose of the transducer is to
sense and convert the static pressure in the supply-side
duct work or the under floor space and convert it to a 4
– 20 ma input. The milliamp input is sent to the Unit
Control and compared against the “Fan-S/A Pres SP”.
The transducer(s) are factory wired, but the pneumatic
tubing must be field supplied and installed (refer to
Section 2 “Installation” in this manual). On VAV units
the duct static pressure transducer measures differential
pressure between the pressure in the duct and a reference
point, usually atmosphere. On FlexSys units the duct
static pressure transducer measures differential pressure
between the under floor space and a reference point.
When verifying transducer operation, the technician
must insert a tee in each of the tubes connected to the
transducer to verify the differential pressure being
applied to the transducer. Once this pressure is known,
a comparison can be made of the duct pressure vs.
output milliamp values from the transducer. To check
the milliamp output from the transducer remove the
wire from the output (S) or (OUT) connection on the
transducer and connect your meter between the end of
the wire and the (S) or (OUT) terminal of the transducer.
Table 22 (for VAV units) and 23 (for FlexSys units)
shows the relationship between the pressure applied
to the duct static pressure transducer and the output
voltage. The output is linear.
TABLE 22 – VAV DUCT STATIC PRESSURE
TRANSDUCER
DIFF PRESS
(IN WC)
MA
OUTPUT
DIFF PRESS
(IN WC)
MA
OUTPUT
0.0 4.0 3.0 13.6
0.5 5.6 3.5 15.2
1.0 7.2 4.0 16.8
1.5 8.8 4.5 18.4
2.0 10.4 5.0 20.0
2.5 12.0
TABLE 23 – FLEXSYS DUCT STATIC PRESSURE
TRANSDUCER
DIFF PRESS
(IN WC)
MA
OUTPUT
DIFF PRESS
(IN WC)
MA
OUTPUT
0.0 4.0 0.15 13.6
0.025 5.6 0.175 15.2
0.050 7.2 0.20 16.8
0.075 8.8 0.225 18.4
0.10 10.4 0.25 20.0
0.125 12.0
8
SECTION 8 – SERVICE
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