Passport 2®/Passport 2 LT™ Service Manual 0070-10-0441 2 - 23
Theory of Operation NIBP Module (P/N 0997-00-0501)
2.4.2 Pressure Transducer, PT1
A Fujikura XFPM-050KPG-P2 transducer was selected for the measurement channel. It
provides a high level output signal which eliminates the need for an external amplifier circuit.
All that is required is a pull-up resistor and compensation capacitor. The -P2, is screened to
maximize performance in designs which will perform a zero cal before each measurement
and a yearly span cal at 150mmHg near room temperature. It also provides a nonlinearity
specification beyond the screening limits which enhances performance.
Adjusting trim pot R81 changes the attenuation factor of the transducer output signal (span
calibration). The nominal gain slope will correspond to the attenuation produced when the
wiper is at the midpoint of its range. With a 28.7kW value for R80 and a 2kW value for
R81, the nominal gain to be used by the software for the measurement channel is 11.29mV
per mmHg. The adjustment range is wide enough to cover the +/-50mV transducer set point
tolerance at the 150mmHg calibration pressure.
2.4.3 Pressure Transducer, PT2
The Fujikura XFPM-050KPG-BP transducer was selected for the over-pressure channel. Due to
a transducer accuracy of ±5.625mmHg over the entire pressure range, the overpressure
transducer must be zero calibrated at 0mmHg in order to operate the measurement duration
timer. This zero calibration must be performed at the time of manufacture, any time a
transducer is replaced, and as part of the yearly service routine for the NIBP module. The -BP
provides a high level output signal which eliminates the need for an external amplifier circuit.
All that is required is a pull-up resistor and compensation capacitor.
Adjusting trim pot R31 effectively zeros the transducer error. With 0mmHg pressure applied
to the transducer input port, R31 is adjusted until the output of the op-amp (U16) is
0.1V±1mV. With a 100kW value for R30, a 3.60kW value for R29, and a 10kW value for
R31, the nominal gain to be used by the software for the over-pressure channel is 12.44mV
per mmHg. The adjustment range is wide enough to cover the +/-67.5mV transducer set
point tolerance at the 0mmHg calibration pressure.
2.4.4 Over-Pressure Detection
There are two methods of keeping the pressure from getting too high. The first method is the
HC16Z1 software based monitoring of the pressure transducer, PT1. When the software
monitors pressure higher than, 295mmHg in Adult mode, 195mmHg in Pediatric or
145mmHg in Neonate mode, the measurement cycle will halt and dump valve, V1 and
bleed valve, V2 shall open to release the pressure in the cuff.
In the event of an over-pressure condition that is not corrected by the HC16Z1 software and
the measurement channel circuitry, the over-pressure channel serves as a fully redundant
backup system to disable the pump and valves, thus relieving the pressure in the cuff. The
hardware over pressure limit detect circuitry will deactivate the over pressure signal
12VEN*, cutting off power to the pump (M1) and valves (V1 and V2), reverting them to their
‘normally open’ state, independent of software. This action places the NIBP PCB in a
‘shutdown’ state that can be exited only by cycling the system power.
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