System Processing Description
70
ARGUS VCM
Service Manual
ARGUS VCM
Temperature Processing
Overview
Patient temperature can be measured via an oral/axillary, rectal, or skin surface probe. A
predictive algorithm in conjunction with the thermistor based thermometer is used for
fast temperature or monitoring temperature.
Predictive temperature
Thermometers that render a temperature reading before steady state is achieved are
classified as predictive thermometers. Predictive thermometers reduce the time required
for measurement by using algorithms to “predict” what the temperature would be if the
probe were left in place until steady state is achieved.
Monitor temperature
A function or mode of an electronic thermometer used to continuously monitor
temperature until it reached the thermal steady state (unchanging). The thermal steady
state is achieved orally in approximately 3 minutes, and axillary in approximately five
minutes.
Measuring Principle
The ARGUS VCM temperature probe utilizes a negative temperature coefficient (NTC)
thermistor and control circuitry in combination with the temperature module’s
predictive algorithm to calculate patient temperatures.
NTC thermistors have a large temperature coefficient of resistance and change in
resistance as temperature changes. This predictable change in resistance is the basis for
predictive thermometry.
The Oral/axillary probe is pre-warmed to approximately 34
℃
(94
℉
). The probe
warming process is a closed loop feedback control system incorporating pulse width
modulation (PWM) control. The probe warmer circuitry is used to heat the probe tip
prior to taking a temperature reading in order to speed the convergence of the
prediction algorithm. A fail safe hardware shut off circuit is included to ensure the
heater will shut down in the event of a software failure.
When the probe is first extracted and colder than 33.9
℃
, the heater pulse
widths are at a maximum percentage On vs Off to warm the probe quickly.
When the probe reached 33.9
℃
, 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 probe being at
least up to 33.1 (9
℃
1.6 )
℉
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 provided.
