Welch Allyn SureTemp 767 - Thermometer Modes (Theory of Operation); Monitor Mode; Normal Mode

Welch Allyn Model 767
display), pressing the Mode Button will wake up the thermometer and display the last recorded Normal
mode temperature.
Thermometer Modes (Theory of Operation)
Monitor Mode
The Monitor mode is selected manually by the Mode button (S1) on the right side of the instrument.
This button, when pressed, ties U1-26 low. When this line (MODE) is held low for more than two
seconds after a normal mode temperature is taken, the thermometer enters Monitor mode.
The actual probe temperature, as determined by the A/D conversion electronics, appears directly on
the liquid crystal display. See the Temperature Measurement and Display section for a description
of the A/D operation.
The displayed temperature range (for any mode) is limited to 84.0°F to 108.0°F(28.9°C to 42.2°C).
Normal Mode
The Oral/Axillary probe is pre-warmed using a pulse width modulation (PWM) controller to 93°F
(33.9°C) upon extraction from the storage well.
· When the probe is first extracted and colder than 93°F(33.9°C), the heater pulse widths are at a
maximum percentage ON vs. OFF to warm the probe quickly.
· When the probe reaches 93°F (33.9°C), the pulse widths narrow to a duty cycle just enough to
maintain temperature.
· When the probe is placed in the mouth, the heat supplied by the mouth makes the pulse widths
reduce to zero. This reduction to zero (and the probe being at least up to 91.6°F(33.1°C) triggers the
start of the prediction algorithm.
The shape of the rising temperature curve is monitored and the best fit to a curve is found. When the
curve fit is stable, the final predicted temperature is displayed.
· In the oral mode, if the prediction criteria is not met within 15 seconds of starting the prediction
process, it will automatically switch to Monitor mode.
· In the axillary mode, if the prediction criteria is not met within 30 seconds of starting the prediction
process, the thermometer displays a final temperature but also indicates that the probe is out of
position.
· In the oral or axillary mode, if the ambient temperature is above 93.0°F (33.9°C) the unit will
automatically switch to Monitor mode.
· Rectal probes are not prewarmed. Rectal temperature measurements will take about 15 seconds.
· Within 60 seconds after the probe is removed from the well, if the prediction process has not
started, the thermometer will switch to Monitor mode.