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ADXRS450 Scheda tecnica(PDF) 9 Page - Analog Devices |
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ADXRS450 Scheda tecnica(HTML) 9 Page - Analog Devices |
9 / 28 page ADXRS450 Rev. 0 | Page 9 of 28 THEORY OF OPERATION The ADXRS450 operates on the principle of a resonator gyro- scope. A simplified version of one of four polysilicon sensing structures is shown in Figure 18. Each sensing structure contains a dither frame that is electrostatically driven to resonance. This produces the necessary velocity element to produce a Coriolis force when experiencing angular rate. In the SOIC_CAV package, the ADXRS450 is designed to sense a z-axis (yaw) angular rate; whereas the vertical mount package (LCC_V) orients the device such that it can sense pitch or roll angular rate on the same PCB. When the sensing structure is exposed to angular rate, the resulting Coriolis force couples into an outer sense frame, which contains movable fingers that are placed between fixed pickoff fingers. This forms a capacitive pickoff structure that senses Coriolis motion. The resulting signal is fed to a series of gain and demodulation stages that produce the electrical rate signal output. The quad sensor design rejects linear and angular acceleration, including external g-forces and vibration. This is achieved by mechanically coupling the four sensing structures such that external g-forces appear as common-mode signals that can be removed by the fully differential architecture implemented in the ADXRS450. X Y Z Figure 18. Simplified Gyroscope Sensing Structure The resonator requires 22.5 V (typical) for operation. Because only 5 V is typically available in most applications, a switching regulator is included on chip. CONTINUOUS SELF-TEST The ADXRS450 gyroscope uses a complete electromechanical self-test . An electrostatic force is applied to the gyroscope frame, resulting in a deflection of the capacitive sense fingers. This deflection is exactly equivalent to deflection that occurs as a result of external rate input. The output from the beam structure is processed by the same signal chain as a true rate output signal, providing complete coverage of the electrical and mechanical components. The electromechanical self-test is performed continuously during operation at a rate higher than the output bandwidth of the device. The self-test routine generates equivalent positive and negative rate deflections. This information can then be filtered with no overall effect on the demodulated rate output. RATE SIGNAL WITH CONTINUOUS SELF TEST SIGNAL. SELF TEST AMPLITUDE. INTERNALLY COMPARED TO THE SPECIFICATION TABLE LIMITS. LOW FREQUENCY RATE INFORMATION. Figure 19. Continuous Self-Test Demodulation The difference amplitude between the positive and negative self-test deflections is filtered to 2 Hz, and it is continuously monitored and compared to hardcoded self-test limits. If the measured amplitude exceeds these limits (listed in Table 1), one of two error conditions asserts depending on the magnitude of self-test error. For less severe self-test error magnitudes, the CST bit of the fault register is asserted; however, the status bits (ST[1:0]) in the sensor data response remain set to 0b01 for valid sensor data. For more severe self-test errors, the CST bit of the fault reg- ister is asserted, and the status bits (ST[1:0]) in the sensor data response are set to 0b00 for invalid sensor data. Table 1 lists the thresholds for both of these failure conditions. If desired, the user can access the self-test information by issuing a read command to the self-test memory register (Address 0x04). For more infor- mation about error reporting, see the SPI Communication Protocol section. |
Codice articolo simile - ADXRS450_11 |
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Descrizione simile - ADXRS450_11 |
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