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ADXRS453 Folha de dados(PDF) 9 Page - Analog Devices |
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ADXRS453 Folha de dados(HTML) 9 Page - Analog Devices |
9 / 32 page ADXRS453 Rev. 0 | Page 9 of 32 THEORY OF OPERATION The ADXRS453 operates on the principle of a resonator gyroscope. Figure 18 shows a simplified version of one of four polysilicon sensing structures. 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 the device experiences angular rate. In the SOIC_CAV package, the ADXRS453 is designed to sense a z-axis (yaw) angular rate; the LCC_V vertical mount package orients the device such that it can sense pitch or roll angular rate on the same PCB. X Y Z Figure 18. Simplified Gyroscope Sensing Structure 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 ADXRS453. 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 ADXRS453 gyroscope implements a complete electro- mechanical 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 both 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 f0/8000 (~1.95 Hz) and is continuously monitored and compared to hard-coded self-test limits. If the measured amplitude exceeds these limits (listed in Table 1), one of two error conditions is asserted, depending on the magnitude of the 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 01 for valid sensor data. • For more severe self-test errors, the CST bit of the fault register is asserted and the status bits (ST[1:0]) in the sensor data response are set to 00 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). See the SPI Communication Protocol section for more informa- tion about error reporting. |
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Descrição semelhante - ADXRS453 |
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