Temperature and Invasive Blood Pressure (Temp/Press) measurement
Introduction to the Instrument
39
Transducer Detection
The transducer being used can be determined by recognising the coding in the connector.
This is done by the transducer detection circuitry. A window comparator checks the input
voltages provided by the transducer against specified limits.
Current Source
The current source generates a constant current for the resistor array that is used to measure
the temperature.
Resistor Array
The constant current is fed through four resistors in series: A test resistor, the externally
connected temperature probe, a gain calibration resistor, and an offset resistor. The voltage
drop across each resistor is sequentially measured and digitized. The CPU controls the
measurement of the different voltage drops and the ADC.
Analog to Digital Converter (ADC)
The ADC receives the pressure signal from the Input Protection Network and the temperature
signal from the Resistor Array. The ADC amplifies, filters, and digitizes the received
pressure or temperature signal. The CPU controls the A/D conversion and accesses the
digitized data for further processing.
Central Processing Unit (CPU)
The CPU controls the ADC and receives the digitized pressure or temperature data from the
ADC. The CPU calculates the temperature values and scales the raw pressure waveform
using stored pressure calibration data. The CPU stores pressure calibration data and user
settings into a non-volatile read/write storage device. The scaled pressure waveform and
temperature data are communicated to the System CPU via a serial interface. The CPU
receives calibration data and user settings from the System CPU.
Temperature and Invasive Pressure Software
The CPU contains software that performs:
• communication with the System CPU
• data acquisition of the invasive pressure signal or temperature
• control of the A/D converter
• pressure wave and temperature numeric filtering
• switching between temperature and pressure measurement depending on the connected
transducer
• INOP and error detection and self-tests
The CPU receives control information from the System CPU and transmits the pressure wave
or a temperature numeric, INOPs and error and status messages to the System CPU.
The CPU software functionality is structured into the following modules (see block diagram):
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