GE b30, Technical Reference Manual

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B30 Patient Monitor
1-46
Document no
.
2044677-001
The standard probe is a finger clamp probe which contains the light source LEDs in one half
and the photodiode detector in the other half. Different kinds of probes are available from GE
Healthcare.
4.6.4 Temperature
The temperature is measured by a probe whose resistance varies when the temperature
changes, called NTC (Negative Temperature Coefficient) resistor.
The resistance can be measured by two complementary methods:
•
Applying a constant voltage across the resistor and measuring the current that flows
through it.
•
Applying a constant current through the resistor and measuring the voltage that is
generated across it.
E-PSM(P)W module uses the constant current method. The NTC-resistor is connected in series
with a normal resistor and a constant current is applied through them. The temperature
dependent voltage can be detected at the junction of the resistors, thus producing the
temperature signal from the patient. The signal is amplified by analog amplifiers and further
processed by digital electronics.
4.6.5 Invasive blood pressure
To measure invasive blood pressure, a catheter is inserted into an artery or vein. The invasive
pressure setup, consisting of a connecting tubing, a pressure transducer, an intravenous bag
of normal saline, all connected together by stopcocks, is attached to the catheter. The
transducer is placed at the same level with the heart, and is electrically zeroed.
The transducer is a piezo-resistive device that converts the pressure signal to a voltage. The
monitor interprets the voltage signal so that pressure data and pressure waveforms can be
displayed.
4.6.6 Respiration
Impedance respiration is measured across the thorax between ECG electrodes. The respiration
signal is made by supplying current between the electrodes and by measuring the differential
current from the electrodes. The signal measured is the impedance change caused by
breathing. The respiration rate is calculated from these impedance changes, and the
respiration waveform is displayed on the screen.