Physitemp Instruments BAT-10 - Manual (Page 4)

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rial. In liquids and semi-solids, the tip and sheath are simply immersed; on solid surfaces, the sheath
is laid against the surface.
Here is a useful rough rule: Heat leakage effects are substantially reduced when an amount
of probe equal to 10 or more sheath diameters is immersed or laid on the surface. For
example, with a probe of 1/16” diameter:
10 x 1/16” = 10/16” = .625” = the minimum immersion depth
11.7 Errors between thermocouple probes. All Physitemp clinical probes and sensors are made with
thermocouple wire that has been specially tested to meet our own stringent standards. Our clinical
probes are guaranteed accurate to within 0.1oC in the range 0-50oC. Copper-Constantan (type T)
thermocouples from other manufacturers are not normally this accurate. Probes made from wire to
“special limits of error” may be accurate to ±0.5°C in this range. This interchangeability of sensor,
including microprobes, is a major advantage of Physitemp thermocouple thermometer
11.8 Measurements in Liquids. These are quite easy to make, because there is good thermal
contact between liquid and probe. The latter quickly reaches liquid tem-
perature and readings can be taken within a few seconds. However, a
liquid which has been heated above or cooled below ambient will be
losing or gaining heat, and convection currents will give rise to tempera-
ture variations of up to several degrees. These variations can be reduced
by vigorous stirring. This simple precaution must always be taken.
11.9 Measurements of Air Temperature. Temperature can vary widely in different parts of a
room; differences of at least several degrees will usually be noted. When a microprobe is used to
indicate air temperature, readings will often fluctuate rapidly, responding to actual temperature
changes caused by air currents. Breathing near the microprobe will produce wide fluctuations.
These effects indicate the sensitivity of the BAT-10/microprobe combination, due to high discrimi-
nation of the instrument and almost instant response of the probe. Fluctuations can easily be elimi-
nated by bringing the probe into contact with a metallic object, thus increasing its effective mass
and slowing the response. Using a larger probe will have the same results.
11.10 Measurements on Solid Surfaces. These are most easily made with surface probes such as
our BT-1 and MT-D. The right-angled tip provides the 10 diameters
of probe contact specified in Section 11.6. Straight probes may also
be used, provided that sufficient shaft length is in contact with the
surface to be measured. In general, the smaller the probe, the more
accurately it will measure the surface temperature of a solid. For
instance, an MT-29 microprobe, because of its small size, needs to
be in contact with the surface for as little as 1/8”. SST-1 has a 1/4” gold disc sensor. Gold is an
excellent conductor, and is non-allergenic and non-polluting. It makes a fine skin surface probe.