D) Measure RTD temperature probe resistance at the connector after
unplugging it from plug J302. The resistance between contacts, at
various temperatures are as follows:
TEMPERATURE . . . . . . . . . . . . RESISTANCE
0°C . . . . . . . . . . . . . . . . . . . . . . . . . . 100 OHMS
20°C . . . . . . . . . . . . . . . . . . . . . . . . . 108 OHMS
37°C . . . . . . . . . . . . . . . . . . . . . . . . . 114 OHMS
50°C . . . . . . . . . . . . . . . . . . . . . . . . . 119 OHMS
Note
Only 2 of the 3 connector positions are used.
s
4. Malfunctioning RTD Temperature probe:
The Control Board can detect if the temperature probe or the connec-
tion of the temperature probe to the circuit board is "OPEN" or
"SHORTED". These two conditions are shown on the display as fol-
lows:
DISPLAY . . . . . . . . . . . . . . . . . . . . CONDITION
. . . . . . . . . . . . . . . . . . . OPEN CIRCUIT
. . . . . . . . . . . . . . SHORT CIRCUIT
Before deciding that the probe is bad when one of these displays
appear, check the connection of the probe to the circuit board.
5. RTD Temperature Sensor Probe Location:
The Proper RTD location is important. The RTD is supported by the
stainless steel bracket attached on the rear wall and near the top of the
chamber. Two tube shaped clips securely support the RTD probe into
place. The RTD must be inserted fully into its support bracket.
6. Constantly Experiencing Low Temperature Alarm:
If the growth chamber is constantly going into low temperature alarm,
then most likely the setpoint temperature setting is too close to the low
temperature alarm/setpoint setting. The setpoint temperature setting
should be a minimum of 2° above the low temperature alarm setting. If
the problem persists, then see Solution 3.
7. Constantly Experiencing High Temperature Alarm:
If the growth chamber is constantly going into high temperature alarm,
then most likely the setpoint temperature setting is too close to the
high temperature alarm/setpoint setting. The setpoint temperature
setting should be a minimum of 2° below the high temperature alarm
setting. If the problem persists, then see Solution 3.
4-6
Plant Growth Chamber
Thermo Scientific
Section 4
Service
Possible Solutions
(continued)
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