Datascope Passport - Mindray

Passport 2 NIBP Module (P/N 0670-00-0730 or 0670-00-0746-01) Theory of Operation
2.15.9 Pressure Transducer, PT2
The Fujikura XFPM-050KPG-BP3 transducer was selected for the over-pressure channel. Due
to a transducer accuracy of ±5.625mmHg (+/-67.5mV set point tolerance at the 0mmHg)
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 is
automatically performed by the software resident in the secondary Atmel microcontroller
(U4). The PT2 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 transducer has an output transfer characteristic of 12mV/mmHg, but due to a small gain
generated by a 100kW value for R30 and a 3.60kW value for R29 in the negative
feedback loop of the op-amp (U16), the transfer characteristic to be used by the software for
the over-pressure channel is 12.44mV/mmHg. With 0mmHg pressure applied to the
transducer input port, the output of the op-amp (U16) is approximately 100mV. Given the set
point tolerance of +/-67.5mVat 0mmHg, the main processor (U10) software tracking can be
off as much as 67.5mV * 3.6% or 69.93mV (5.62mmHg).
The transducer is not inserted until the end of the manufacturing and cleaning processes,
avoiding exposure to moisture which may effect its performance, but will be soldered in
place after final assembly.
2.15.10 12VSW Circuitry, Q1, Q2
Disabling the pump (M1) and valves (V1 and V2) is accomplished by cutting power to these
devices using a switched version of 12V2, 12VSW. This is done via the secondary
microcontroller’s 12VEN* signal which controls Q1. The 12VEN* signal turns the NPN
transistor Q1 on which allows current to flow through R36 and into the Q1 collector. The
voltage developed on R36 turns on Q2, a P-channel FET with high current capability,
supplying power to the pump and valves.
2.15.11 Primary Microcontroller, U10
The NIBP PCB utilizes a Motorola MC68HC16Z1CPV16 microcontroller. This specifies a 5V,
16.78MHz, commercial temperature range part in a 144 pin TQFP package. This processor
is responsible for controlling a pump and two valves in the generation of the patient pressure
signal. This data is processed by the HC16Z1 and fed to the host via an RS-485 interface
through the processor’s SCI port.
A 32.768kHz crystal (Y1) is used for the HC16Z1 reference oscillator circuit. The HC16Z1
SYNCR (clock synthesizer control) register will be set with X=1, W=0 and Y=60. This
produces a nominal system clock frequency of 15.99MHz. The 32.768kHz crystal is
specified with a load capacitance of 20pF. To present this load, C20 and C21 are set to
33pF. The load capacitance is calculated as the series combination of C21 and C22 plus the
stray capacitance which is estimated to be less than 5pF.
At Power-On Reset, the state of the HC16Z1 pins controlling the pump and valves is such that
they are disabled (pump off / valves open).
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