2-24 250cx Series Maternal/Fetal Monitor Revision C
2036947-001
Equipment Overview: Theory of Operation
digitized and sent over the barrier via an opto coupler where it is routed similarly to
the FECG analog signal.
The uterine pressure front-end processes the pressure signals from the external
TOCO or IUP sensor (uses same inputs) by amplifying and filtering the inputs and
converts the signals via serial analog to digital converter. The output of the A/D
converter is then sent across the isolation barrier, routed through the front-end
motherboard through to the DSP PWA where it is further processed. Two mode
lines from the UA patient connector are also digitized, TOCO present and IUP
present (only one cable can be plugged in at a time). These signals are then sent over
the barrier via an opto- couplers where they are routed similarly to the TOCO/IUP
digitized signals.
MECG PWA
The MECG PWA processes the isolated MECG signals present from the ECG front
panel connector. The multi-lead signals first go through programmable lead switching
circuitry controlled by the DSP processor. The MECG signal is then amplified and
filtered and sent across the isolation barrier where it is routed through the front-end
motherboard to the DSP PWA, digitized and processed. The MECG PWA also
contains an ECG test signal on the isolated side which is used when the monitor front
panel test button is depressed. This tests most of the front-end circuitry paths. The
MECG PWA also contains pacemaker detection circuitry allowing the monitor to
blank out the pulses for proper counting.
Ultrasound PWA
The dual ultrasound PWA generates the ultrasound timing signals to pulse the external
patient connected ultrasound transducer crystals and provides the necessary receive
circuitry to detect the reflected waveforms. It does this by first demodulating the needed
signal off of the carrier and filtering the signals which are then sent through the front-
end motherboard to the DSP where they are digitized and processed. No isolation is
present from the patient connector through the ultrasound board as the plastic
ultrasound transducer forms the physical isolation barrier.
Isolated Power Supply PWA
The isolated power supply provides all of the isolated power for the FECG/UA
PWA, MECG PWA and the carrier PWA which in turn feeds the two SpO
2
modules
(MSpO
2
). The ultrasound PWA is not powered from this board as it is not
electrically isolated. The isolated power supply is made up of two isolated sets of
supplies. One supply set is specifically for FECG on the FECG/UA PWA. The other
isolated set of supplies powers the remaining functions including TOCO/IUP (on the
FECG/UA PWA), MECG (MECG board), and the SpO
2
Carrier PWA (SpO
2
modules). The unisolated power input to this PWA consists of +20 volts routed from
the front-end motherboard through the DSP and Main PWAs and then finally the
system power supply.
Front-End Motherboard PWA
The front-end motherboard PWA is a passive inter-connection board which houses
all of the front-end parameters except for NIBP. In addition to the parameters, it
holds the isolated power supply. The PWA routes all of the isolated and un-isolated
signals to and from the DSP PWA. This includes both analog and digital parameter
inputs and digital control outputs. On the front-end side it interfaces to the pressure
channel front-end cable and the FECG front-end cable, which carries all of the
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