Nbp Board; Nbp Board With Dinamap Or Marquette Electronics Technology; Pressure Transducer And Amplifier; Dc Pressure Amplifier And Filter - GE Corometrics 126 Service Manual

NBP Board

NBP Board with DINAMAP or Marquette Electronics Technology

Pressure Transducer and Amplifier

DC Pressure Amplifier and Filter

Revision B
Theory of Operation: NBP Board
Depending on when your monitor was manufactured, your unit may have one of
three blood pressure boards installed:
Manufactured by GE Medical Systems Information Technologies with
DINAMAP blood pressure technology
Manufactured by GE Marquette with Marquette Electronics blood pressure
technology
Manufactured by CAS Medical Systems, Inc. with CAS blood pressure
technology
Refer to "Chapter 14, Replacement Parts"
The pressure transducer used in the NBP module is a Motorola SPX4053 (PS1)
which is a 0 to 7.3 PSI sensor. The scale factor for this sensor is 10.595 µV/V/
mmHg. The transducer uses 10 Vdc to drive the sensor resulting in an output of
105.96 µV/mmHg. The transducer output is amplified by three stages of
instrumentation amplifier U14 with a gain of 249.
The output of the pressure sensor instrumentation amplifier connects to a unity-gain
two-pole 18 Hz low-pass filter (U14). The filter output connects to a DC amplifier
(U13) which provides a gain of 1.9, and offsets the 0 mmHg pressure output to –9V.
In the NBP module, the 10 V sensor drive is used as a reference to provide offset.
The output of this amplifier stage provides the cuff pressure signal to the A/D
converter and processor.

AC Amplifier and Filter

The output of the 18 Hz low-pass filter also provides the input to a two stage high-
pass filter (U13) with gain and baseline restoration. Both stages are composed of a
0.7 Hz R/C high-pass filter buffered by a non-inverting amplifier. The first stage
buffer amplifier has a gain of 82.6, and the second stage operates at unity gain. This
filter chain extracts the small varying pressure signal caused by blood flow from the
DC pressure signal to provide the pulse waveform needed to process the blood
pressure measurement. The input of both buffer amplifiers (after the series high-
pass capacitors) have FET switches (Q1, Q2) connected to ground. These switches
clamp the inputs of the buffer amplifiers to ground when activated. The switches are
activated during valve operation to prevent large signal transition from occurring in
these stages when air is released from the cuff. The effect also provides a baseline
restoration to 0 V at the output of these stages. Control of these FET clamps are
from a processor output port through a transistor level shifter. The outputs of the
high-pass stages connect to a two-pole 12 Hz unity gain low-pass filter (U13), which
further restricts the AC passband. The composite 3 dB passband points with both
high-pass and both low-pass filters is 1 Hz and 11 Hz. After the output of the low-
pass filter, the signal divides into two paths. One path provides a unity gain (U12) to
the A/D for higher level signals; the other provides a gain of 5 (U12) for lower
amplitude signals. Both of these outputs, along with the DC pressure signal, are
120 Series Maternal/Fetal Monitor
2015590-001
for NBP board part numbers.
4-35