Welch Allyn Diatek 600, Technical Manual

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Technical Manual
Model 600 9
The normal mode temperature cycle is terminated when the predicted temperature remains stable for
several seconds.
SELF TESTS
Internal Calibration Test
The calibration test is performed only once during a temperature taking cycle and occurs during the
display test. Upon completion of the first calibration cycle, the resistance of R4 is measured and
compared against limits stored in the microprocessor memory. The specified limits are 5740 and 5780
ohms. If the resistance calculated by the microprocessor when the pulse width of R4 is measured does
not fall within these limits, the malfunction error is displayed.
Internal Microprocessor Memory Test
The microprocessor memory test is performed only once during a temperature taking cycle and occurs
during the display test. Each 8 bit byte of program memory is divided into two 4 bit nibbles which are
summed. The total sum of all nibbles and a special check sum compensation nibble must be O or the
malfunction error is displayed.
Broken Probe Test
Each probe resistance sample that is taken is checked to see that it lies between 2000 and 60,000
ohms. A resistance value outside of these limits will cause a broken probe error to be displayed.
DISPLAY
Display Voltage Reference
Diodes CR2-CR6. Q7, R61 and R7 create the display voltage references of about (V+)—1 volt at U2-
25 (V+)—2 volts at U2-24 and (V+)—3 volts at U2-23.
Display
The liquid crystal display is of the 4 backplane multiplexed type (quadraplex), requires a regulated
operating voltage, and is driven directly by the microprocessor.
Horn
The microprocessor provides a control signal to U1-3 which is the feedback input for the horn driver
contained in U1. The horn driver output (U1-l) drives the horn (H1) at its self resonant frequency of
about 6 kHz.
Backlight
The microprocessor activates the backlight by setting U2-4 high. This signal is inverted and buffered
and reappears at U1-13 going low. A low level on U1-13 turns on the backlight inverter circuit
consisting of Q1, Q2, R1, R2, C5 and T1. The inverter supplies an AC voltage of about 80 volts and
300 Hz to the Electroluminescent panel BP1. CR7 blocks negative voltage spikes from entering U1-13.