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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 17. 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 17 – TEMPERATURE SENSOR
RESISTANCE
RESISTANCE
° F
(OHMS)
-25
196,300
-20
165,100
-15
139,300
-10
118,000
-5
100,200
0
85,350
5
72,910
10
62,480
15
53,640
20
46,230
25
39,910
30
34,560
35
30,000
40
26,100
45
27,760
50
19,900
55
17,440
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
JOHNSON CONTROLS
SECTION 8 – SERVICE
RESISTANCE
° F
(OHMS)
60
15,310
65
13,480
70
11,880
75
10,500
80
9,298
85
8,250
90
7,331
95
6,532
100
5,826
105
5,209
110
4,663
115
4,182
120
3,757
125
3,381
130
3,047
135
2,750
140
2,486
duct work or the under fl oor 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 fi eld 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 fl oor 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 18 (for VAV units) and Table 19 (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 18 – VAV DUCT STATIC PRESSURE
TRANSDUCER
DIFF PRESS
MA
(IN WC)
OUTPUT
0.0
4.0
0.5
5.6
1.0
7.2
1.5
8.8
2.0
10.4
2.5
12.0
TABLE 19 – FLEXSYS DUCT STATIC PRESSURE
TRANSDUCER
DIFF PRESS
MA
(IN WC)
OUTPUT
0.0
4.0
0.025
5.6
0.050
7.2
0.075
8.8
0.10
10.4
0.125
12.0
FORM 145.05-NOM2 (807)
DIFF PRESS
MA
(IN WC)
OUTPUT
3.0
13.6
3.5
15.2
4.0
16.8
4.5
18.4
5.0
20.0
DIFF PRESS
MA
(IN WC)
OUTPUT
0.15
13.6
0.175
15.2
0.20
16.8
0.225
18.4
0.25
20.0
95
8
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