Welch Allyn Diatek 600, Техническое руководство

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Diatek, A Welch Allyn Company
8 Model 600
2. The low battery detector output (Ul-9) is tested by the microprocessor. A low logic level on Ul-9
indicates a low battery condition (less than 3.0 volts).
3. The horn drive signal (U2-11) goes high activating the horn test for 0.1 second.
4. The backlight switch, normal/monitor switch and F/C switches are tested by the microprocessor.
5. A calibration cycle is performed.
6. The calibration test is performed.
7. The microprocessor memory test is performed.
8. The probe resistance is tested for an open or shorted condition.
Following the events which take place during the display test, a continuous monitor mode temperature
measurement or a predict mode temperature taking cycle is started.
Probe Temperature Measurement
Q3-Q6, Q8, R3-R5, R-16, C2 and U1 comprise a unique resistance to pulse width conversion circuit
which allows any one of 4 resistance’s to be measured by the microprocessor. The circuit allows the
microprocessor to select precision resistors with equivalent temperatures at opposite ends of the
temperature measurement range and measure their relative pulse widths.
The microprocessor sets U2- 16 to 19 high as required to select the appropriate resistance to be
measured. R3 provides a pulse width calibration at 93.2 °F, R5 provides calibration at 106.9 °F and R3
is used for a calibration test at 100.5 °F. A ratiometeric calculation is used to compute the probe
resistance from its pulse width relative to those provided by R3 and R5. The accuracy of each
calibration resistor is .05 °F. A resistance to pulse width conversion is initiated by the microprocessor
setting U2-64 high for approximately 0.5 seconds with the appropriate FET switch selected sometime
within that period. U2-64 is then set low and the time from this transition until the A/D output (U1-2)
goes high is measured by the microprocessor. The crystal X1 provides the time base for the pulse
width measurements. The probe temperature is computed using the probe resistance value obtained
from the ratiometeric pulse width calculations.
Monitor Mode Operation
In the monitor mode a new probe temperature measurement is completed every 1.5 seconds and a
new calibration cycle is completed every 3 seconds. The computed probe temperature is displayed
directly on the liquid crystal display and will follow both upward and downward movement.
Normal Mode Operation
In the normal mode. a new probe temperature measurement is completed every 1.5 seconds. At least
one calibration cycle is performed at the start of a predict cycle and continue every 3 seconds until the
probe temperature rises above 84.0 °F. The calibration cycle is stopped at this point to reduce
quantizing errors associated with the measurement of the slowly changing probe temperature.
The normal mode displayed temperature is the sum of the actual probe temperature and a computed
correction factor which is based on the shape of the changing temperature curve at that point in time.
The values of the correction factor can vary from 0 °F to 2.3 °F with a typical value when the horn
sounds of about 1 °F. During the display test prior to starting a normal mode temperature cycle, the
ambient temperature of the probe is measured and is used in the correction factor computation to
adjust for differing probe starting conditions. The normal mode display is peak reading and therefore
the highest temperature is displayed even though the present predicted probe temperature may drop.