Honeywell Electronic Remote Temperature Controller T775J - Manual (Page 17)

T775J ELECTRONIC REMOTE TEMPERATURE CONTROLLER
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Display
Once power is applied or restored to the device, the display
will count down from 210 until the display reads zero, during
which time any previously energized outputs will be de-
energized. This is intended to protect compressors in the
event of a power outage.
To avoid viewing this entire countdown, press the Select key.
The LCD display will now show what it normally reads: load
(sensed) temperature, stages energized, and which Sensor
(A or B) is being read. At any time during the programming or
review procedure, the display will revert back to showing the
sensed temperature and stage status indication 60 seconds
after the last key closure.
The user has three display options to select. The display can
be configured to alternately indicate Sensor A and Sensor B
sensed temperature at a five second rate or the display can
be locked on to sensor A or sensor B to sense temperature
continuously.
This selection is accomplished by stopping at Sensor A or
Sensor B sensed temperature points in the Select key
scrolling loop. To lock on to either sensor, the user must scroll
the Select key through the loop to select the sensed
temperature prompt desired. The display will stick to that
parameter until the Select key is activated to advance the
loop. When the loop is stopped at any other prompt, the
display will alternately indicate Sensor A and Sensor B
sensed temperatures after 60 seconds from the last key
closure or immediately after the Select key is pressed at the
end of the programming sequence.
Error Messages
There are seven error messages that can be displayed in
response to software or hardware problems with the T775J.
The error codes that may be seen flashing on the display are:
SF—Sensor Failure.
The display flashing SF indicates an out-of-range
sensor. Make sure the sensors are properly
connected. For the T775J, stage 2 load will be de-
energized when this error message is flashing for
Sensor B. When this message is flashing for Sensor
A only, stage 1 will
not be de-energized.
EF—EEPROM Failure.
The values read back from the EEPROM are not the
same as written into the EEPROM. The EEPROM is
not intended for field repair. Replace the device.
CF—Calibration Failure.
A calibration resistor reading was not within the range
of the Analog to Digital converter. This error message
can not be field repaired. Replace the device.
OF—Stray interrupt Failure.
An unused interrupt occurred. This error cannot be
field repaired. Replace the device.
CE—Configuration Error.
The device hardware was configured to a nonexistent
device. This error cannot be field repaired. Replace
the device.
OE—ROM Error.
The internal ROM of the microprocessor is defective.
This error cannot be field repaired. Replace the
device.
AE—RAM Error
The internal RAM of the microprocessor is defective.
This error cannot be field repaired. Replace the
device.
Setpoint Calibration
To maintain temperature accuracy, sensor wires should be 18
AWG two-conductor (18/2). If the length of the sensor wire
exceeds 400 feet, recalibration will be necessary to maintain
accuracy (see Fig. 21). Table 2 shows the corresponding
temperature offset that should be used for different sensor
wire lengths. This temperature offset should be added to the
desired temperature setpoint for these applications.
RESISTANCE
(OHMS)
4200
4000
3800
3600
3400
3200
20 40 60 80 100 120 140 160 180 200 220
-7 0 10 20 30 40 50 60 70 80 90 100
F
C
3484 ± 6.5 OHMS
AT 77°F (25°C)
M2829 TEMPERATURE (DEGREES)
Fig. 21. Resistance versus temperature
performance characteristics.
Table 2. Sensor Wire Length/Calibration Offset
(Using 18 Awg Wire).
Sensor Wire Length (ft) Calibration Offset (°)
0-399 None required.
400-599 1
600-799 2
800-1000 3