Temperature Sensors In Use - Wahl Heat-Prober 392AHP User Manual

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Heat-Prober Platinum-RTD Thermometers User Manual
Thus at 200°C, the expected sensor error could be 0.3°C + .0054 (200) =±1.38°C.

3.2 Temperature Sensors in Use

An understanding of heat-transfer is needed for accurate field use of temperature sensors. The
sensor measures its own temperature, therefore, to measure a body temperature it requires
good contact with that body, or in the case of liquids or gases good immersion and mixing.
A portable probe temperature sensor must have the following characteristics:
(a) a low thermal mass (product of its specific heat and weight);
(b) a large area for surface contact to permit heat-transfer between the object being measured
and the probe sensor,
(c) a minimum of heat conduction away from the sensor which will reduce its temperature below
that of the object being measured and create an inaccuracy.
Surface probes are designed with the above three conditions as criteria, and also include an
insulating handle for your safety and convenience. Each probe is assembled with a plastic
handle made of high quality Delrin® which:
(a) Thermally isolates the hand from the probe, preventing hand heat from reaching the sensor,
and sensor heat, in the case of high temperature measurement, from burning the hand.
(b) Electrically isolating the hand from the metal probes and therefore, potentially, from a
voltage on the surface to be measured.
The handle is attached to a tangle-free retractable cord which extends 6' and retracts to 12"
(See Figure 2-1). Each Probe is labeled with its part number and type.
For surface measurements, to obtain best time responses and accuracy, two things are
necessary;
(a) Good surface contact with all of the probe surface. Make sure of this by holding it squarely
on the surface. The 121 and 145 surface probes are specially designed with a spring loaded tip
to provide compliance with the surface.
(b) A rough surface gives poor heat conductance to the measuring probe. This can be
overcome by applying a thin layer of heat conducting silicone paste between the measuring
point and the probe tip. The paste shortens response time up to 50%.
In liquids, move the immersion probe around the mix to get good contact. In air, put the probe in
the vicinity of a stream to get good velocity, otherwise move the probe back and forth to induce
velocity across the tip.
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