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An accelerometer is an electromechanical device for measuring the change of linear motion (=dynamic acceleration) as well as gravitational forces (=static acceleration). The direction of the gravitational force (1 g = 9.8m/s²) with respect to the device is used to calculate the orientation of the device. Accelerometers measure the acceleration in one, two, or three orthogonal axes.
To use an accelerometer in a portable device, it is necessary to measure all three axes.
Absolute accuracy: Difference between measured value and true absolute pressure reference.
Relative accuracy: Difference between two measurements while temperature or pressure have changed. Is a measure for the repeatability of the sensor.
Application programming interface – is a specified interface which allows the system software to address the MEMS sensors.
An application-specific integrated circuit is an integrated circuit (IC) designed for a particular application.
The bandwidth of a sensor describes the frequency dependence of the electrical output sensitivity with respect to the input.
A barometric pressure sensor measures the absolute ambient air pressure. The air pressure depends on the altitude and also varies due to weather changes. With a barometric pressure sensor applications for weather forecast (barometer), sports (altimeter), indoor navigation (floor tracking) and GPS improvement (faster time to first fix by tight coupling) can be realized.
See “DRIE” for more information.
Chip scale package – packaging technology that enables chip housings with dimensions that are only slightly bigger (max. 1.2 times) than the die itself.
The cross-axis sensitivity describes the output sensitivity of an axis when the sensor is accelerated perpendicularly to this axis.
The angle between geographic north and magnetic north from the observer’s location.
The Bosch Sensortec Development Board is a hardware tool that Bosch Sensortec provides to its customers for evaluating Bosch Sensortec MEMS sensors in a convenient manner. It comes together with the so-called Development Desktop software which allows watching measurement data on a standard PC while at the same time controlling all the parameters of the sensor.
Is a small, functional piece of microelectronic or micromechanical wafer material without any packaging.
6Dof and 9DoF stand for 6 respectively 9 Degrees-of-Freedom. One Degree-of-Freedom is represented by one dimension / axis of a sensor. In that way, a 3-axis accelerometer represents a 3DoF device. An IMU, consisting of an accelerometer and a gyroscope represent a 6DoF device. A device consisting of an IMU and a geo-magnetic sensor is regarded as a 9DoF device.
Deep-reactive ion etching - is a process technology that allows manufacturing MEMS microstructures with extremely high precision. This process technology has been invented by Robert Bosch GmbH (“Bosch” process).
6-axis sensor module consisting of a 3-axis geomagnetic sensor and a 3-axis accelerometer in package.
Bosch Sensortec proprietary geomagnetic sensor technology.
Bosch Sensortec´s FusionLib software intelligently processes raw data from multiple sensors into a single optimized solution, characterized by fast response, high data throughput and low power.
Sensor, designed to measure the direction and strength of the earth magnetic field.
3 axes are necessary.
The earth magnetic field. Its magnitude is 20 to 60 µT depending on the geographical location.
The imaginary line drawn around earth halfway between the geographic north and south pole.
Point where earth’s rotation axis crosses earth’s surface in the northern hemisphere.
Point where earth’s rotation axis crosses earth’s surface in the southern hemisphere.
In principle, a gyroscope is a device for measuring changes of orientation, based on the principles of angular momentum. MEMS gyroscopes are used for measuring the rate of rotation in space (roll, pitch and yaw) also referred to as “angular rate”. The physical unit of the measured data is “degrees per second”. Degrees per second is also referred to as “dps” or “ °/s ”.
Direction of user movement correlated to magnetic north.
Inter IC bus - is a serial, two-wire data bus used for the communication between microelectronic devices.
In electronic systems “interrupts” are commonly used to signal certain states to a µController or another processing unit. In the context of MEMS sensors interrupts are used to signal certain states that have been detected by the logic integrated within the MEMS sensor to the attached µController or system-host processor.
Certain states, threshold values and timings can be programmed to the sensor and then autonomously detected by the sensor while measurements are done.
Example: An “any-motion” interrupt function of an accelerometer detects when a certain, pre-defined level of acceleration is exceeded and it sends an interrupt signal via its interrupt pin to the host controller of the system.
Inertial Measurement Unit - a device which combines a 3-axis acceleration sensor and a 3-axis gyroscope.
Angle between the direction of the earth magnetic field and the horizontal plane at the according location. Roughly, in the northern hemisphere, it is positive, in the southern hemisphere, it is negative.
Least significant bit – it represents the smallest measured value that can be represented in a digital system.
Stands for land-grid array, a state-of-the-art packaging technology used for microelectronic products.
The location near the geographic south pole where the inclination of earth’s magnetic field is -90° and the magnetic field lines crosses earth’s surface.
The measurement range is the span between minimum and maximum value that can be measured by the sensor.
Accelerometer: measured in multiples of the gravitational force “g” (1g = 9.81m/s²), so the measurement ranges are e.g. +/-2g / +/-4g, …
Barometric pressure sensor: operating pressure range providing full accuracy,measured in hPa, e.g. 300…1100hPa
Geomagnetic sensor: range measured in µT …, important for z-axis since permanent magnetic disturbances in heandheld devices occur mainly in z-axis direction.
Micro-electro-mechanical system – the combination of micro-mechanics and micro-electronics in one system or device.
The noise value quantifies the fluctuation of the electrical output signal at constant mechanical input. The noise is given either as peak-to-peak (pp) or root-mean-square value (rms).
Nonlinearity is the maximum deviation of the electrical output signal from the sensitivity (best fit straight line) given in percent of the full scale measurement range.
Resolution corresponds to the smallest change of the input signal that leads to a detectable change of the electrical output signal.
Sensitivity is defined as the change of the electrical output signal with respect to the change of the physical input signal: S=delta_out/delta_a
System in Package – Multiple sensors and microcontroller in one package
Soft magnetic materials amplifying or distorting magnetic fields. Their magnetization is easily changed by magnetic fields.
Serial peripheral interface bus - is a serial, 4-wire (sometimes also 3-wire) data bus used for the communication between microelectronic devices.
The offset (e.g. zero-g offset for accelerometers) itself is temperature-dependent. The values for the offset in the datasheet are given for TA=25°C. If the temperature is different from 25°C, the zero-g-offset changes as given by the TCO.
Pressure sensors: Pa/K
Magnetic sensors: µT/K
The sensitivity itself is temperature-dependent. Often the values for sensitivity in the datasheet are given only for TA=25°C. If the temperature is different from 25°C, the sensitivity then changes as given by the TCS. Units:
Accelerometers, gyroscopes, magnetic sensors: %/K
Pressure sensors: as the pressure sensor is usually not operated at zero pressure but around 1 atmosphere, this effect has been included in the specified TCO already.
Is a technology for packaging microelectronic devices directly at wafer-level with the resulting package dimensions very close to the size of the die itself.
The zero-g offset of an accelerometer is the value of the electrical output signal when the sensor is at rest and the detection direction perpendicular to the gravitational force.