Chapter 3 – Operation
TestEquity 101H Temperature/Humidity Chamber
Page 15
Performance Considerations
The performance of all chambers is significantly affected by the characteristics of your test
sample. Factors include size, weight, material, shape, and power dissipation if energized.
The test sample should be placed in the chamber in a manner that allows for air circulation. The
air plenum is located on the back wall of the chamber, where air is sucked in from the left side
and exits from the right side. You should not place the test sample directly on the chamber floor.
It should be placed on the shelf. Multiple test samples should be distributed throughout the
chamber to ensure even airflow and minimize temperature gradients. If necessary, an additional
shelf should be used to evenly distribute the load. Verify that the temperature gradients are
within acceptable limits, by measuring the chamber temperature at strategic points using a
multipoint thermocouple meter or data logger.
You may find that the temperature throughout the chamber is even, but always different from
what the temperature controller indicates. The correct way to adjust what the temperature
controller “displays” compared to what is measured at some point other than the controller’s
sensor is with the “Calibration Offset” parameter.
Avoiding Moisture (non-humidity mode)
Any time the ambient air is subjected to temperatures below the dew point, moisture will
condense out of the air. The effect is ice or frost during low temperature operation. When the
chamber is heated above 0°C, the ice or frost will turn into water.
To avoid moisture condensation, make sure the port plugs are inserted with the gray silicone
surfaces facing the inside and outside of the chamber at all times. Any air gaps between the wires
going through the ports will create a path for moisture migration and thermal losses. Also, avoid
opening the chamber door while the chamber is operating at temperatures below room ambient.
When a low temperature test is completed, warm the chamber to at least room ambient before
opening the chamber door and before removing your test sample.
You CANNOT use the humidity system to control moisture at low temperatures. The humidity
system is disabled below +7°C. However, if you have a source of GN
2
(gaseous nitrogen) or Dry
Air, you can use the Purge system to eliminate moisture condensation at low temperatures.
Internal Test Fixtures
Some applications require internal fixtures to support test samples and provide a convenient
method of connecting wires and sensors. Fixtures must be designed to minimize their impact on
chamber functionality and performance.
Fixtures should be designed for easy removal to permit maintenance and cleaning of the
chamber. The chamber liner should never be drilled or screwed into. This will compromise the
integrity of the liner and permit moisture migration due to condensation into the insulation,
which will eventually impact performance and lead to premature rusting of the outer cabinet.
Fixtures should be constructed of stainless steel. This also applies to all screws and fasteners. All
welds should be passivated. To prevent rust and corrosion, never use iron or mild steel even if it
is painted or plated. Aluminum may be used. However, since the specific heat of aluminum is
double that of steel, it represents a greater load and will have more impact on the chamber
performance.
