Thermo Scientific 3403 Manual page 48

Section 8
Appendices
8-16 Midi 40 CO2 Incubator
TP10 "RTD1" (continued)
• The H2O / Tank RTD probe is indicating a temperature significantly
below set point (typically results in condensation on the walls).
• Large cabinet temperature offset (single loop operation).
• Heat source near top of the unit.
• A poorly insulated steam generator (conditioning cabinet probe).
It should be remembered that the H2O / Tank RTD probe plays a new
role in the control of the water temperature from previous designs. In
single loop mode (default), The H2O / Tank heater PWM is determined
by the Cabinet RTD probe. If the H2O / Tank RTD exceeds the set point
be 0.1°C, the PWM will be clipped to zero. In dual loop mode, the H2O
/ Tank RTD probe determines the PWM for the H2O / Tank heater. In
this case, the temperature that will be controlled to, will be the set point
minus the H20 Adjust variable ("ADJDeltaH2O").
TP11 "RTD2"
Ambient RTD located at the top rear of the incubator. TP11 will typi-
cally be in the ~100-103mV range (reference Table 7.5 after TP12
"RTD3"). There are no control implications with this sensor. This sen-
sor is useful if environmental conditions are suspect. Also useful for
swapping RTD's if a CPU A/D channel is suspect.
TP12 "RTD3"
Cabinet RTD located in top center of the interior of the incubator.
With a set point of 37.0°C and 0.0°C offset, TP12 should be in the 107
mV range. Keep in mind that most DMM's are not that accurate when
reading millivolts. In a reciprocal fashion, if set point is 37.0°C and the
offset is 0.0°C, then approximately 106.9 mV is present at TP12. In
most cases, the accuracy of the DMM can be gauged by how closely it
reflects this value.
value from the RTD, i.e. 20-40°C, count on this information being cor-
rect. Again, the issue most likely to be encountered with this sensor is
conditioning. Conditioning typically leads to greater than desired probe
to center air offsets, which in turn can lead to condensation.
Conditioning of the cabinet probe can usually be traced to an improper-
ly isolated steam generator or another source of heat on top of the
incubator.
As discussed earlier, if you are getting a reasonable
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