Welch Allyn Medical Diagnostic Equipment Thermometer 690 Manual De Usuario
71221-0000 Rev. H
23
5. Theory of Operation
5.1
Technical Overview
The SureTemp
®
Plus Model 690 and 692 are portable, battery powered thermistor-based
medical grade thermometers that perform oral, axillary, and rectal measurements using high-
speed prediction modes.
speed prediction modes.
The devices perform a power-on self test (POST) when battery power is applied. POST
checks the internal hardware, and tests the stored calibration values to verify that the factory
calibration is intact. When a thermometer probe is connected, the device reads data from the
probe to determine the type of probe and probe calibration values. The thermometer will go
into Low Power mode when inactive to maximize battery life.
checks the internal hardware, and tests the stored calibration values to verify that the factory
calibration is intact. When a thermometer probe is connected, the device reads data from the
probe to determine the type of probe and probe calibration values. The thermometer will go
into Low Power mode when inactive to maximize battery life.
A predict measurement cycle is initiated when a connected thermometer probe is pulled from
the probe well of the device. When the probe is pulled from the probe well the optical probe
detection switch wakes up the microprocessor and a measurement cycle begins. The device
pre-heats the probe tip (Oral and Axillary only) to create a stable thermal environment at the
probe tip. When the tip is applied to the patient the tip heater is turned off. The thermistor value
is monitored by the microprocessor and other internal circuitry. The microprocessor uses
internal modes to process the thermistor data and calculate a patient’s temperature. The
temperature data is then displayed to the user on the LCD. It is also possible to switch the
thermometer to Monitor mode, which displays real-time data from the thermistor.
the probe well of the device. When the probe is pulled from the probe well the optical probe
detection switch wakes up the microprocessor and a measurement cycle begins. The device
pre-heats the probe tip (Oral and Axillary only) to create a stable thermal environment at the
probe tip. When the tip is applied to the patient the tip heater is turned off. The thermistor value
is monitored by the microprocessor and other internal circuitry. The microprocessor uses
internal modes to process the thermistor data and calculate a patient’s temperature. The
temperature data is then displayed to the user on the LCD. It is also possible to switch the
thermometer to Monitor mode, which displays real-time data from the thermistor.
The Model 692 thermometer includes a backlit LCD for viewing in low ambient light conditions
and a security mode that disables device operation when used outside the programmed
security parameters.
and a security mode that disables device operation when used outside the programmed
security parameters.
Figure 3: Model 690 and 692 Thermometers System Block Diagram
Q t y = 3 A A
B a t t e r i e s
R e g u l a t e d A n a l o g
P o w e r S u p p l y
M i c r o p r o c e s s o r
E E P R O M
C u s t o m L C D
A n a l o g C i r c u i t r y
P r o b e A n a l o g
I n t e r f a c e
K e y p a d
A n a l o g t o D i g i t a l
C o n v e r s i o n
B e e p e r
P O W E R C O N D I T I O N I N G
P r o b e D i g i t a l
I n t e r f a c e
S y s t e m O u t p u t s
S y s t e m I n p u t s
S u r e T e m p P l u s S y s t e m B l o c k D i a g r a m
S e c u r i t y S w i t c h
( 6 9 2 O n l y )
O p t i c a l P r o b e
S w i t c h
I n t e r n a l S y s t e m
S e r i a l I n t e r f a c e
( W e l c h A l l y n
F a c t o r y U s e O n l y )