Gaymar MEDI-THERM II MTA5900 Series, Руководство по обслуживанию

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SERVICE MANUAL
Medi-Therm II THEORY OF OPERATION
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.com P/N 10187-000 7/98
Temperature measurement is achieved using 400 series thermistor beads located
in the blanket water path (blanket water probe RT2), the cold water reservoir
(cold water reservoir probe RT1), and in the patient via the patient probe jack J1.
Under microprocessor U37 control, each of the three beads is connected to
the current source circuitry (U38 and associated components) by a
demultiplexor U49. At the same time, the resulting output voltage created by
the current through the thermistor is presented to an amplifier circuit (U39
and associated components) via multiplexor U50. The amplified voltage is then
applied to a voltage-to-frequency converter U24. A frequency up to 100kHz is
presented to port pin P3.5 of the microprocessor. The microprocessor
converts the incoming frequency to a temperature value.
At regular intervals two compensation resistors R13 and R12 are also
processed in the same manner. These compensation resistors are precision
resistors with values at each end of the probe temperature range of 32°F
(0°C) to 122°F (50°C). The values from the precision resistors are used to
compensate for circuit drift.
User input is entered via a digital control panel. The input from the buttons is
decoded by U45. The “data available” line of U45 is tied to the microprocessor
port pin P3.3. When a button press is decoded and debounced by U45, the
“data available” line goes high and the microprocessor responds by inputting
the decoded value.
For display of measured and set point temperatures, 7 segment LED displays
are utilized:
• The set point display is driven by driver chip U48. The
microprocessor interfaces to it via the data bus at addresses 0FFF8H,
0FFF9H, 0FFFAH, 0FFFBH.
• The patient display is driven by driver chip U6. The microprocessor
interfaces to it via the data bus at addresses 0FFF4H, 0FFF5H,
0FFF6H, 0FFF7H.
• The blanket display is driven by driver chip U5. The microprocessor
interfaces to it via the data bus at addresses 0FFECH, 0FFEDH, 0FFEEH,
0FFEFH.
6.4.1 THERMISTOR
OUTPUT
MEASUREMENT
6.4.2 DIGITAL CONTROL
PANEL INPUT
6.4.3 DISPLAY UPDATE
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