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5 • Circuit Descriptions
80116-443
10.16
Description of the various assemblies
Processor board
Pressure sensor
The pressure sensor records the back pressure and transmits this using
the internal AD converter to the processor.
The pressure sensor is a 68.8 hPa (1 psi) sensor and is neither compensat-
ed nor calibrated. It is fed via a constant-current source. The pressure sen-
sor measuring bridge is then read in via a difference amplifier with a gain
of 133 by the processor AD converter. The pressure sensor has a full-scale
output signal of 20 mV. A gain of 133 gives a voltage of 2.66 V for 69 hPa.
To adjust the zero output a potentiometer is provided. The amplitude is not
adjusted, since the absolute value is not decisive for the evaluation of the
occlusion (system blocked).
Temperature sensor
For the temperature sensor a temperature-dependent resistor is used.
This is read into the processor via the AD converter.
Controller Supervisor
The assembly has three functions:
Function 1 The controller supervisor keeps the controller in Reset while the voltages
are ramping up.
Function 2 The controller supervisor detects a power-fail and sends a message to the
controller on the interrupt input. It is now possible for the controller to
store the current settings and to operate in a safe status.
Processor: MC68HC912BC32
Quartz: 16 MHz
ADC: The AD converter inputs are filtered by an RC element
Manufacturer: SensorTechnics
Type: SX01DD4
Type: B57620-C103
Resistor value: at 25 °C = 10 kOhm
Series resistor: 10 kOhm
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