Trio™ Service Manual
0070-10-0591-01
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Theory of Operation
Parameter Circuit Descriptions
The sensor measurement wavelengths are nominally 660 nm for the Red LED and 940 nm for
the Infrared LED. Maximum optical power output for LED is 4 mW. The amount of light
transmitted depends on many factors, most of which are constant. However, one of these
factors, arterial blood flow, varies with time because it is pulsating. By measuring the light
absorption during a pulsation, it is possible to derive the oxygen saturation of the arterial
blood. Detecting the pulsation gives a pleth waveform and pulse rate signal. The SpO
2
value
and the pleth waveform can be displayed on the main screen.
1.4.5
Temperature
The temperature circuit can amplify and filter the input signal of the temperature probe and
then output it into the A/D sampling circuit on the ECG/RESP board. This circuit consists of
sampling switching, constant-current supply, signal amplifier, filter and probe detector. The
output signal of the circuit has clamping protection to ensure that the output voltage is less
than VCC. The circuit also has a self-calibrating function.
1.4.6
IBP (optional)
Invasive Blood Pressure monitors arterial pressure, central venous pressure and pulmonary
arterial pressure.
IBP may be measured by inserting the catheter into the appropriate blood vessel. The end of
the catheter, located outside the human body, should connect directly to the pressure
transducer.
Inject normal saline into the catheter. Since the liquid can transfer pressure, the pressure
inside the blood vessel can be transferred to the outside pressure transducer. In this way we
can obtain the waveform of the dynamic pressure inside the vessel. Systolic, diastolic and
mean pressures are calculated by using an algorithm.
