Abstract: The United States produced by Motorola MPX2100 pressure sensor working principle of composition based on MPX2100 Digital pressure gauge, and V / F converter application circuit.
Keywords: pressure sensor MPX2100 voltage and frequency conversion digital pressure gauge
MPX2100 manufactured by Motorola, the semiconductor pressure sensor can be converted to millivolt pressure differential mode voltage signal, the pressure sensor has good linearity, its output voltage and the applied pressure into precise proportional relationship. In addition, MPX2100 the compensation characteristics with temperature is pressure-sensitive semiconductor devices to overcome the existing problem of temperature drift, which has broad application prospects.
MPX2100 has 4 pins, 1 foot ground, 3 feet plus the working pressure, 2 feet and 4 feet between the output and the pressure differential is proportional to the voltage signal.
MPX2100 is a piezoresistive pressure sensor, with the proliferation of a silicon chip resistor process into 4 equal to the strain components, the Wheatstone bridge. Bridge with constant voltage source power supply and two constant current source power supply. Constant source of power by the schematic shown in Figure 1.
When under pressure when the pressure sensor, a pair of leg resistance value increases R, another arm of the resistance of the bridge to reduce R, R the change of resistance is proportional to the pressure, that is R = KP, the bridge output voltage Uo = E (R / R) = (EK / R) P, the bridge output voltage proportional to the pressure P.
2 digital manometer based MPX2100
MPX2100 form shown in Figure 2 digital manometer. MPX2100 working voltage of 12V, the sensor 4 feet and 2 feet between the output pressure signal to IC1, IC2 amplification, the amplifier gain of 1 +40 / RP1, IC1, IC2 connected in-phase input resistance state, you can get equipment the required high input impedance amplifier; IC3 is a unity gain differential amplifier, which can achieve high CMRR, IC4 and RP2 zero voltage divider circuit form, RP1 is used to adjust the gain of the amplifier circuit to complete the full pressure range of the display of digital calibration. IC3 output voltage is applied to A / D converter IC5 of the analog voltage input (31 feet), converted into digital by IC5 to drive the LED display shows the size of the pressure.
3 voltage frequency converter
Figure 3 shows the voltage formed by the MPX2100 frequency conversion circuit. The circuit voltage by the amplification and frequency conversion of two parts, by a 4-op-amp and some resistors amplifier, it has a height-mode gain and high common mode rejection ratio, and high input impedance, you can adjust the bias. Differential amplification circuit completed mainly by A1, A2 is used to prevent the op amp feedback circuit into the sensor’s negative terminal. At zero pressure, the sensor 2 feet and 4 feet difference between the voltage zero. If 2 feet and 4 feet each for the common mode voltage of 4V (half of the sensor supply voltage), the A1 1-pin voltage is 4V, so that the voltage through the A3 and A4 road to make it zero pressure output voltage. Zero pressure offset output by the introduction of R4 and R12, R12 can be set to adjust the bias voltage. Through R7 can choose from 13 feet to see past the resistance, typically 1kO. Amplifier gain AV = R5 [1 + (R11/R10)> / R6 = 125. Select a gain of 125 allows the sensor full-scale output swing 32mV to 4V when the swing amplification.
A3 output of 0.5 ~ 4.5V output voltage by the V / F transform can output 1 ~ 10kHz frequency. A3 of 8 feet and AD654V / F converter is connected. The full-scale output frequency of the R3, R13 and C3 decisions, and can be calculated according to the following formula:
Fout (full scale) = Vin / [10 (R3 + R15) C3>
For best performance, R3 and R13 should be chosen so that AD654 3-feet when full-scale current of 1mA drive. AD654 input stage is an op amp, so it’s 3 feet and 4 feet equivalent voltage (virtual short), so that full-scale, 3 pin voltage is 4.5V, R3 + R13 is about 4.5kO, therefore, flow R3 and R13 in the current 4.5V/4.5k = 1mA. That is, R3 + R13 once given, C3 will determine the V / F full-scale output frequency. R13 tuning frequency can be adjusted to achieve full scale. Zero-pressure frequency adjustment can be achieved by adjusting R12. Frequency output of the edge transition speed can be a small signal FET inverter to improve (BS107A), the circuit’s final output of the counter with a microcontroller-compatible input.
MPX2100 semiconductor pressure sensor for pressure detection to provide a cost-effective and reliable method, therefore, it will be widely used in many fields.