Passport 2 NIBP Module (P/N 0670-00-0730 or 0670-00-0746-01)
Theory of Operation
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0070-10-0441
Passport 2®/Passport 2 LT™ Service Manual
R15 and R27 are +/-0.1% tolerance, +/-25ppm/°C resistors which form a highly accurate
and stable voltage divider generating the AD7714 2.5V reference voltage from A5V. Since
the PT1 measurement channel transducer output is ratiometric with A5V, the AD7714
readings are directly proportional to the applied pressure after subtracting the zero offset.
The DRDY* signal is used to indicate to the HC16Z1 software that the converted data is
available. The AD7714’s POL input is tied low, so the HC16Z1 QSPI shall be configured in
the master mode with its CPOL bit set to 0 and its CPHA bit set to 1 for ADC data transfers.
The nominal ADC clock rate is 2MHz.
2.15.4
DAC
The linear valve’s bleed rate is current controlled by the HC16Z1 software by writing to a
Maxim MAX5352 12-bit DAC (U12) connected to a Burr-Brown OPA336 CMOS
operational amplifier (U13), in turn connected to an International Rectifier IRF7303 Power
MOSFET (Q6).
A DAC code of 0 will result in zero current flow in Q6, and a fully opened valve. A full-scale
DAC code results in the maximum DAC output voltage of 2.5V and thus maximum current
flow in Q6. This corresponds to a fully closed valve. Power-on-reset clears the DAC’s output
to 0 thus fully opening the valve. The DAC’s 2.5V reference voltage is derived from a Linear
Technology part, LT1790-2.5.
2.15.5
Pump, M1
The pump control signal, M1EN, is provided via a PWM signal from the HC16Z1
microcontroller and is active high. This signal switches MOSFET Q3 (1/2), applying power
to the pump motor. Power to the pump (12VSW) is supplied from 12V2 via Q2. This allows
the pump to be disabled in case of a fault condition.
2.15.6
Dump Valve, V1
The dump valve, V1, is controlled by the V1EN signal provided by an active high signal from
the HC16Z1 microcontroller. This signal drives MOSFET Q3 (1/2), which switches power to
the valve coil. Power to the valve (12VSW) is supplied from 12V2 via Q2. This allows the
valve to be opened in case of a fault condition. This valve is a ‘normally open’ type, so coil
current must be supplied to cause the valve to close.
2.15.7
Linear Valve, V2
The linear valve, V2, provides bleed down of the cuff pressure. The HC16Z1 software
maintains the pressure bleed rate at a nominal 6mmHg per second, for product specified
volumes and pressure ranges. The linear valve can also be used to control the pump up rate
when small volume cuffs are used in the neonatal mode.
Note that this valve is a ‘normally open’ type, so coil current must be supplied to cause the
valve to close.
