This paper introduces the Deli Kang’s BP01-type pressure sensor and the main performance parameters of a given sensors with BP01 as a portable electronic device in the actual circuit, and the working principle of the application circuit are described, and gives the The portable electronic device circuit design and debugging methods.
Keywords: pressure sensor; portable electronic device; BP01
BP01-type pressure sensor is specifically designed for monitoring blood pressure, mainly used in portable electronic devices. It uses precision thick-film ceramic chip and nylon plastic package with high linearity, low noise and small features of the external stress; using the internal calibration and temperature compensation to improve the measurement accuracy, stability and repeatability, in the whole scale range, accuracy ± 1%, zero offset is less than ± 300µV.
The main performance parameters of 2 BP01
BP01’s internal equivalent circuit shown in Figure 1 and outline package; Table 1 lists the power supply voltage Vs for the BP01 5.0V, 25 ambient temperature when the TA is the main performance parameters.
BP01 limit parameters are as follows:
Maximum operating voltage: 20VDC;
Great pressure: 1500 mmHg;
Operating temperature range: 0 ~ 70 ?;
Pin Soldering Temperature (max): 250 ? (2 ~ 4 seconds).
3, the electronic device based on BP01
Formed with the BP01 portable electronic device of the principle circuit shown in Figure 2, which consists of bias power supply circuit (A1, A2), pre-processing circuit (A3 ~ A6), the display circuit (A7) and pressure sensors (BP01) composition, the blood pressure monitor blood pressure measurement range of 0 ~ 200mmHg, a resolution of 0.1mmHg, the power supply is a 9V laminated battery. Blood pressure in the main circuit now works are as follows:
a. bias supply circuit
Power circuit with a built-in reference voltage by the dual op amp LM10 composition, A1-phase amplifier constitute, A2 constitute follower, their role is to enlarge the built-in reference voltage as a pressure sensor BP01 after the bias voltage Vs, the Vs value is determined by:
Vs = Vref (1 + R2/R3)
Where: Vref for the LM10 chip reference voltage. The value of 200mV, this value together with R2 and R3 in the circuit values into the above equation can be obtained on behalf of the bias voltage Vs of the value of 5V.
b. pre-processing circuit
Pre-processing circuit consists of four operational amplifiers A3 ~ A6, of which constitute the disorder A3 on the circuit offset bias circuit to compensate; A5 constitute a follower for the output of pressure sensor signals BP01 isolation buffer; A4, A6 form amplifier, the gain of AV is determined by:
AV = 1 + (R1/RT)
If neglected disorders, pre-processing circuit’s output voltage Vout is:
Vout = 2 (1 + R1/RT) VIN
Where: VIN BP01 for the pressure sensor output voltage.
c. display circuit
Display circuit used three and a half display driver. Work, the output of pressure sensor BP01 amplified by the pre-processing circuit, the display driver circuit to drive the LCD, to read out the measurement of blood pressure.
3.2 Debugging Methods
a. adjust the zero pressure output
In the zero pressure output, adjust the offset potentiometer RP1, the display value of 000.0 in blood pressure, they can think to complete the zero-pressure output adjustments.
b. Adjustment of pre-gain of the circuit
Pressure sensor BP01 full-scale output offset voltage and a certain relationship, when the 5V bias at 200mmHg pressure output of 10mV, the corresponding display driver circuit input 200mV, so AV is the gain of the circuit pre- 200mV/10mV, so use the formula in front of Av can gain resistance against introduction of the value of RT.
If you select resistor R1 is 10kO, the gain resistors RT should be 1.1kO. Debugging can be the first potentiometer to adjust the output value, then meter measured the resistance of the potentiometer, and finally replaced by a fixed resistor.
c. adjustment of full scale
Full-scale adjustment, the first in the show circuit with the input voltage is 200mV, and then adjust the potentiometer RP2, so that it can be read as 199.9mmHg.
The adjustment is completed, should be more generally repeated several times, so that the displayed value reliably meet the required precision.
3.3 The selection of components
To ensure accuracy, the choice of external components the circuit is also an important part can not be ignored. Under normal circumstances, potentiometer RP1, RP2 should use 1% precision metal film multi-turn potentiometer; resistance should be used in the precision of 1% metal film resistors; capacitor is generally used in polyester film or mica capacitors.
BP01 in the use of pressure sensors and other devices designed portable electronic device, it should be noted that: for different bias voltage, the output is different, so the gain of pre-processing circuit to be adjusted accordingly to meet the full range of different requirements.