Gonzales, Jamil M. Tengedan, Billy R.
Accelerometer Gonzales, Jamil M. Tengedan, Billy R. Accelerometer An accelerometer is an electromechanical devicethat will measure acceleration forces. These forces may be: Static, like the constant force of gravity pulling atyour feet. Dynamic - caused by moving or vibrating theaccelerometer. Common Functions By measuring the amount of staticacceleration due to gravity, you canfind out the angle the device is tilted atwith respect to the earth. By sensing the amount of dynamicacceleration, you can analyze the waythe device is moving. How do accelerometer work?
Piezoelectric effect - they contain microscopiccrystal structures that get stressed by accelerativeforces, which causes a voltage to be generated. Sensing changes in capacitance - If anaccelerative force moves one of the structures,then the capacitance will change. Piezoresistive effect, Hot air bubbles, and Light. Piezoelectric Effect is the ability of certain materials to generate an electric charge in response to applied mechanical stress Number of axes - For most projects, two is enough
Number of axes - For most projects, two isenough. However, if you want to attempt 3dpositioning, you will need a 3 axisaccelerometer, or two 2 axis ones mounted atright angles. Maximum swing - If you only care aboutmeasuring tilt using earth's gravity, a 1.5gaccelerometer will be more than enough. Ifyou are going to use the accelerometer tomeasure the motion of a car, plane orrobot, 2g should give you enoughheadroom to work with. For a project thatexperiences very sudden starts or stops, youwill need one that can handle 5g or more. Although the symbol is sometimes used for standard gravity, (without a suffix) can also mean the local acceleration due to local gravity and centrifugal acceleration, which varies depending on one's position on Earth (see Earth's gravity). Sensitivity - Generally speaking, the more sensitivity the better
Sensitivity - Generally speaking, the more sensitivity the better.This means that for a given change in acceleration, there willbe a larger change in signal. Since larger signal changes areeasier to measure, you will get more accurate readings. Bandwidth - This means the amount of times per second youcan take a reliable acceleration reading. For slow moving tiltsensing applications, a bandwidth of 50Hz will probablysuffice. If you intend to do vibration measurement, or control afast moving machine, you will want a bandwidth of severalhundred Hz. Applications Engineering
Accelerometers can be used to measure vehicle acceleration. Accelerometers can be used to measure vibration oncars, machines, buildings, process control systems andsafety installations. Accelerometers are increasingly being incorporatedinto personal electronic devices to detect theorientation of the device, for example, a display screen. Specification (ADXL335) From Analog Devices THEORY OF OPERATION The sensor is a polysilicon surface-micromachined structure built on top of a 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 plates attached to the moving mass. The fixed plates are driven by 180 out-of-phase square waves. Acceleration deflects the moving mass and unbalances the differential capacitor resulting in a sensor output whose amplitude is proportional to acceleration. Phase-sensitive demodulation techniques are then used to determine the magnitude and direction of the acceleration. The ADXL335 is a complete 3-axis acceleration measurement system. The ADXL335 has a measurement range of 3 g minimum. It contains a polysilicon surface-micromachined sensor and signal conditioning circuitry to implement an open-loop acceleration measurement architecture. The output signals are analog voltages that are proportional to acceleration. The accelerometer can measure the static acceleration of gravity in tilt-sensing applications as well as dynamic acceleration resulting from motion, shock, or vibration. Block Diagram Pin Configuration Pin Description Sources https://www.sparkfun.com/datasheets/Components/S MD/adxl335.pdf