Temperature Probes; Probe Switch; Normal Mode Description - Welch Allyn SureTemp 986 Service Manual

Appendix A. Theory of Operation
A.1.1 Temperature Probes
A.1.2 Probe Switch
A.1.3 Normal Mode Description
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Model 986 thermometers are configured at the factory for
Oral/Axillary or Rectal probe types. The probe type is configured at
the factory by the absence or presence of the MODE jumpers JP1
through JP4.
•
Axillary temperatures are measured with oral probes in
combination with the axillary mode algorithm, and provide a
temperature reading in about 10 seconds.
•
Rectal temperatures are measured with rectal probes in
combination with the rectal mode algorithm, and provide a
Normal mode temperature in about 15 seconds.
Model 986 oral probes have a warming resistor in the tip to pre-
warm the probe before placement in the mouth, thus speeding
typical response.
The probe shaft activates the probe switch (S1) when the probe is
installed or removed from its storage well. Placing the probe into
the well pulls microprocessor pin 76 high via an internal pull up
resistor. When the probe is removed, this line is pulled low. This
signal is also routed to test connector J2 pin 3 to allow automated
testing of this function during factory test.
CAUTION: J2 provides a convenient set of test points to monitor
proper operation of all user switch functions. BE
CAREFUL WITH STATIC DISCHARGE! J2 ties
directly to CMOS processor inputs, which are easily
damaged by static discharge. Follow proper static
handling techniques.
The Oral probe is pre-warmed using a pulse width modulation
(PWM) controller to 33.9°C (93°F) upon extraction from the
storage well. When the probe is first extracted and colder than
33.9°C, the pulse widths are at a maximum percentage ON vs.
OFF to warm the probe quickly. When the probe reaches 33.9°C,
the pulse widths narrow to a duty cycle just high enough to
maintain temperature.
When the probe is placed in the mouth, the heat supplied by the
mouth causes the pulse widths to reduce to zero. This reduction to
zero (and the probe being at least up to 33.1°C) triggers the start
of the prediction algorithm.
70995-0000B M986