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Accelerometers are electronic devices that measure amplitude and phase relationships of varying vibration points of a structure or environment. This type of device is commonly used for seismic vibrations, where sensors are placed at different spots on a bridge, building, or even the ground. The planted devices measure the vibrations of these environments and detect structural changes that may be caused by natural disasters like earthquakes, human activity like construction or mining, and even large vehicles. These devices must be accurate to ensure correct results and ultimately, are a means to determine the safety of an environment and a precautionary measure. The accuracy of these devices is determined by an accelerometer calibrator, which measures and corrects the functioning of the device.
An accelerometer calibrator is usually a small electronic device with a square or rectangular shape that is easily portable to a field environment, like outdoors at a mining site. The standard accelerometer calibrator consists of a vibration exciter that is battery powered and self contained. This exciter measures, verifies, and calibrates an accelerometer’s sensitivity and can determine how accurate it is to within a millionth decimal value. Its internal controls and the excitement system provide a continuous and exact frequency. A separate closed loop simultaneously maintains a consistent amplitude that is independent of a particular test article’s mass.
Like other electronic devices, accelerometers are subject to degradation and wear, so these devices need to be checked consistently by an accelerometer calibrator for accuracy and proper functioning. Voltage from measuring and providing readouts degrades the device, and an accelerometer calibrator will adjust the device based on the voltage output. Fixing the accelerometer device, however, will not make it more accurate and would require another calibration. Accelerometer calibrators currently have an accuracy between 10 ppm and 1 ppm. The more accurate designs are usually made with stronger and better material, but are less cost effective.
The function of an accelerometer calibrator is to read the accelerometer’s output values. The device is read at angular positions that are equally spaced around a horizontal axis. The vertical plane represents the sensitivity axis, and the accelerometer calibrator seeks to align these two axes as closely as possible at a central point. The device can be calibrated either by four points or three points. Final calibration is solved through a complex series of mathematical equations with variables including frequency, acceleration, and amplitude, among others.