42 Thermocouple Probes OVEN TRACKER XL2
In assessing oven performance, to ensure repeatability and ease of use, test-
pieces or test-fixtures with permanently mounted thermocouples should be
used whenever possible.
The presence of a probe on the product will inevitably affect the product’s
temperature: it adds to its thermal mass and thus changes, however slightly, the
rate of heating and cooling. Probes of large thermal mass are unsuitable for use
with small, lightweight products.
Placing a probe between the source of heat and the product can affect the rate
of heating. To minimize the effect, attach the probe to the product’s unheated
side where possible, and/or reduce the probe’s thermal mass.
Glass-fiber or mineral insulation must be used if thermocouple cables are close
to infra-red heating elements or are subject to temperatures over 260°C/500°F.
Route cables to ensure that they are:
• Secured in position along their length.
• Not fouling elements in the oven.
• Not thermally shading the product.
• Not too close to heater elements.
Probe Attachment
The tip of the thermocouple probe must be in good mechanical contact with
the product when monitoring surface temperature. Poor thermal contact will at
best result in slowing the rate at which the product heats the probe and at worst
prevent the probe from achieving the same temperature. Ensure probe tips are
clean before attaching.
The following methods may be used.
Surface Measurement
• Adhesive (patch) A self-adhesive, rapid-response probe recommended
for all small test-pieces and materials less than 1.0 mm/0.04 in. thick. Attach
to the product, test-piece or test-fixture using high-temperature adhesive
tape. When attached to a re-usable test-piece or test-fixture, the probe
may be coated with powder/paint enabling reliable, repeatable beneath-
coating temperature measurements to be made; this is a major advantage
when using infra-red heaters as the absorption of radiation, and thus heat, is
affected by the coating’s color.
• Bolt-on (washer) A rapid-response probe normally permanently
mounted on a re-usable test-piece or test-fixture. Provides reliable,
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