Datex-Ohmeda S/5 PRESTN, Technical Reference Manual Slot

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Datex-Ohmeda S/5 monitors
20
Document No. 8005571-1
Invasive blood pressure measurement unit
An is5 V voltage is supplied to the pressure transducer. The differential voltage, which
depends on the pressure and the supplied voltage, is calculated from the bridge connection (see
the formula below).
U
out
= U
in
×
pressure
×
5 V, where U
in
is 5 V
⇒
U
out
= 25 V
×
pressure [mmHg]
Pressure amplification is realized in the instrumentation amplifier. The gain of the amplifier is set to
keep the level of the signal transferred to A/D converter within the measurement range even when
there are circumstantial offsets or offsets caused by the transducer. There is a filter before the
amplifier to attenuate high frequency disturbances.
Input
Filter
Instrumentation
amplifier
to A D converter
Pressure
transducer
Vin
Vout
G
pressure_meas_pri
nci
p
le
.vsd
Figure 9 Pressure measurement principle
Pulse oximetry measurement section
LED control signals
The D/A converters of the microcontroller on STP board set the LED intensity adjustment values for
the infrared- and red LEDs of SpO2 probe. The microcontroller on the STP board switches ON ( to
the adjusted intensity ) and OFF the SpO2 probe LEDs according to the predetermined sequence.
LED driving circuit
Differential amplifiers measure the LED currents (LED current indication) of SpO2 probe over the
shunt resistors placed in the LED current paths. The LED driving voltages (LED voltage indication)
are measured from the driver circuitry. The LED driving circuits also have MOSFET transistor matrix
to enable the use of different probe configurations.
Measured signal preamplification
The preamplifier is bipolar/single-ended current-to-voltage converter with adjustable gain. A higher
gain is used for measuring thin tissue. The preamplification stage has also ambient light reduction
and second amplifier stage.