Makora At this point a pin is available on each channel to allow the user to set the signal bandwidth of the device by adding a capacitor. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Deflection of the structure is measured using a differential capacitor that consists of independent fixed plates and central plates attached to the moving mass. The analog output signal will be ratiometric to the supply voltage. The sensor is a surface micromachined polysilicon structure built on top of the silicon wafer. The advantage of this method is that the full 5 kHz bandwidth arxl the accelerometer is available to the user.
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The outputs are digital signals whose duty cycles ratio of pulsewidth to period are proportional to the acceleration in each of the 2 sensitive axes. The output period is adjustable from 0. The typical noise floor is ? B Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Box , Norwood, MA , U. Analog Devices, Inc. Supply 0 g Offset vs. Addition of filter capacitor will increase turn on time. Please see the Application section on power cycling.
All min and max specifications are guaranteed. Typical specifications are not tested or guaranteed. Specifications subject to change without notice. Indefinite Operating Temperature. This is a stress rating only; the functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Care should be exercised in handling to avoid damage. The output values shown are nominal. They are presented to show the user what type of response to expect from each of the output pins due to changes in orientation with respect to the Earth. The ADXL reacts similarly with output changes appropriate to its scale. Electrostatic charges as high as V readily accumulate on the human body and test equipment and can discharge without detection.
Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality. C 85 Figure 2. Temperature Figure 5. Typical Zero g Offset vs. Temperature Figure 6. Typical Turn-On Time 0. C Figure 4. Typical Supply Current vs. Temperature Figure 7. F Hz 2 —0. F Hz 0. F 50Hz 0. T2 Length of the total cycle. They contain a polysilicon surface-micromachined sensor and signal conditioning circuitry to implement an open loop acceleration measurement architecture.
The accelerometer measures static acceleration forces such as gravity, allowing it to be used as a tilt sensor. The sensor is a surface micromachined polysilicon structure built on top of the silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide a resistance against acceleration forces.
Deflection of the structure is measured using a differential capacitor that consists of independent fixed plates and central plates attached to the moving mass. An acceleration will deflect the beam and unbalance the differential capacitor, resulting in an output square wave whose amplitude is proportional to acceleration.
Phase sensitive demodulation techniques are then used to rectify the signal and determine the direction of the acceleration. The output of the demodulator drives a duty cycle modulator DCM stage through a 32 k? At this point a pin is available on each channel to allow the user to set the signal bandwidth of the device by adding a capacitor. This filtering improves measurement resolution and helps prevent aliasing.
After being low-pass filtered, the analog signal is converted to a duty cycle modulated signal by the DCM stage. A single resistor sets the period for a complete cycle T2 , which can be set between 0. For most applications a single 0. F capacitor, CDC , will adequately decouple the accelerometer from signal and noise on the power supply.
If additional decoupling is needed, a ? A proper design will take into account the application requirements for bandwidth, signal resolution and acquisition time, as discussed in the following sections. These two pins should be connected directly together. These two pins should be connected directly together and Pin 7 grounded. VTP This pin is to be left open; make no connections of any kind to this pin. When this pin is set to VDD, an electrostatic force is exerted on the beam of the accelerometer.
The resulting movement of the beam allows the user to test if the accelerometer is functional. This pin may be left open circuit or connected to common in normal use. T2 does not have to be measured for every measurement cycle. It need only be updated to account for changes due to temperature, a relatively slow process. Decoding algorithms for various microcontrollers have been developed. Consult the appropriate Application Note.
B Figure Capacitors must be added at these pins to implement low-pass filtering for antialiasing and noise reduction. A minimum capacitance of pF for C X, Y is required in all cases. Table I. Use an RSET value between k? Its higher sensitivity Specific code sets, reference designs, and application notes are available from the factory. This section will outline a general design procedure and discuss the various trade-offs that need to be considered.
The designer should have some idea of the required performance of the system in terms of: Resolution: the smallest signal change that needs to be detected. Bandwidth: the highest frequency that needs to be detected. Acquisition Time: the time that will be available to acquire the signal on each axis. These requirements will help to determine the accelerometer bandwidth, the speed of the microcontroller clock and the length of the T2 period.
When selecting a microcontroller it is helpful to have a counter timer port available. The microcontroller should have provisions for software calibration. A k? The device is designed to operate at duty cycle periods between 0. The easiest way to null this offset is with a calibration factor saved on the microcontroller or by a user calibration for zero g. Table IV. F rms Noise 1.
Filtering can be used to lower the noise floor and improve the resolution of the accelerometer. The user must filter the signal at this point to limit aliasing errors. This will result in greater dynamic error generated at the DCM. The analog bandwidth may be further decreased to reduce noise and improve resolution.
It is recommended that the user limit bandwidth to the lowest frequency needed by the application, to maximize the resolution and dynamic range of the accelerometer. At Hz the noise will be:? Peak-to-peak noise can only be estimated by statistical methods. Table III is useful for estimating the probabilities of exceeding various peak values, given the rms value.
Table III. The second relates to the measurement resolution of the counter when decoding the duty cycle output. The actual resolution of the acceleration signal is, however, limited by the time resolution of the counting devices used to decode the duty cycle. The faster the counter clock, the higher the resolution of the duty cycle and the shorter the T2 period can be for a given resolution. The following table shows some of the trade-offs. Table V. Rate 1. An accelerometer uses the force of gravity as an input vector to determine orientation of an object in space.
An accelerometer is most sensitive to tilt when its sensitive axis is perpendicular to the force of gravity, i. At this orientation its sensitivity to changes in tilt is highest. When the accelerometer is oriented on axis to gravity, i.
ADXL202 DATASHEET PDF
Akim The accelerometer can measure static acceleration forces such as gravity, allowing it to be used as a tilt datasheeg. Although the ADXLE features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Duty Cycle Filtering An analog output can be reconstructed by filtering the duty cycle output. Run the accelerometer at datasheeg Lower Voltage, Down to 3 V. When this pin is set to VDD, an electrostatic force is exerted on the beam of the accelerometer.
ADXL202 Analog Devices, Inc., ADXL202 Datasheet