Power Loss; Temperature Sensor Calibration - Honeywell T775A Series Installation Instructions Manual

CHECKOUT
Inspect all wiring connections at the controller terminals,
and verify compliance with the installation wiring
diagrams.
WARNING
Electrical Shock Hazard.
Can cause severe injury, death or property
damage.
Disconnect power supply before beginning wiring
or making wiring connections, to prevent electrical
shock or equipment damage.
If any wiring changes are required, first be sure to remove
power from the controller before starting work. Pay
particular attention to verifying the power connection (24,
120, or 240 Vac).
After the controller is installed and wired, apply power.

Power Loss

The date and time settings are retained for 24 hours after
a power outage. After a power loss of more than 24 hours,
the date and time settings may need to be reentered. All
other settings are stored permanently.

Temperature Sensor Calibration

As wire length increases, resistance increases and thus
the temperature reading increases. If necessary, calibrate
the sensor input by reducing the value by the amount
shown in the Table 3. For example, a wire run with 18
gauge wire of 1,000 feet, requires a calibration offset of
-6.0° F (-21° C).
IMPORTANT
If the calibration value in the table exceeds the
controller's calibration limits of +/-10° F (+/-6° C),
you must use a heavier gauge wire.
For example, with a wire run of 1,000 feet you
must use 20 AWG wire or heavier in order to
calibrate for wire loss within the limits of the
controller.
See "2.2.2.2. CALIBRATE (the sensor)" on page 18 for
the instructions to enter the calibration value.
All manuals and user guides at all-guides.com
T775A/B/M SERIES 2000 ELECTRONIC STAND-ALONE CONTROLLERS
Table 3. Temperature Sensor Calibration for Resis-
14
16
18
20
22
14
16
18
20
22
a
This is the distance from the controller to the sensor
(already accounts for round trip distance).
Fig. 23 shows how sensor resistance varies with
temperature for a sensor having a positive temperature
coefficient (PTC) of 2.1 Ohms per degree F (3.85 Ohms
per degree C)
.
RESISTANCE (OHMS)
1489
1403
1317
1231
1145
1059
973
887
801
1
11
tance Loss Due to Wire Length.
Temperature Offset in
AWG
Rating mΩ/ft 200 ft
2.5 0.46
4.0 0.72
6.4 1.16
10.2 1.86
16.1 2.92
Temperature Offset in
AWG
Rating mΩ/m 100 m
8.3 0.44
13.2 0.68
21.0 1.10
33.5 1.74
52.8 2.74
1097 ± 0.08 OHMS
AT 77°F (25°C)
1
-40 -20 0 20 40 60 80 100 120 140 160 180 200 220
-40 -30 -20 -10 0 10 20 30 40
TEMPERATURE (DEGREES)
POSITIVE TEMPERATURE COEFFICIENT (PTC) OF 2.1 OHMS PER °F
Fig. 23. Sensor Resistance vs. Temperature.
a
°F (Foot)
500 ft 1,000 ft
1.14 2.28
1.82 3.64
2.90 5.82
4.64 9.28
7.32 14.64
a
°C (Meter)
200 m 300 m
0.86 1.30
1.38 2.06
2.18 3.28
3.48 5.22
5.48 8.22
250 °F
50 60 70 80 90 100 110 120 °C
M24304
62-0254—13