Electronic accelerometers

Every accelerometer has a response curve of the type shown schematically in Figure 4-222. Instead of having an ideal linear response, a nonlinear response is generally obtained with a skewed acceleration for zero current, a scale factor error and a nonlinearity error. In addition, the skew and the errors vary with temperature. If the skew and all the errors are small or compensated in the accelerometer s electronic circuits, the signal read is an ideal response and can be used directly to calculate the borehole inclination. If not, modeling must be resorted to, i.e., making a correction with a computer, generally placed at the surface, to find the ideal response. This correction takes account of the skew,... 

In order to show how the properties of the cavity can be used to develop a chemi-cal/biological sensor, the nature of sensor needs to be outlined. What is a sensor In simplistic terms, it is a device that is equipped with proper electronics to quantify changes in a given state of a system. It may be an accelerometer of an automobile, emission gas temperature of a jetliner, environment, bio-metabolism of living bodies, space storms, etc. What is required is a way to detect subtle changes. ... 

Most automobile airbags contain sodium azide (NaNj) as the propellant. When accelerometers detecta crash, the electronic controllerfiresthe charge of sodium azide. Sodium azide decomposes explosively, generating nitrogen gas that fills the airbag. 

L. M. Roylance and J. B. Angell, A batch-fabricated silicon accelerometer, IEEE Trans. Electron Devices 26(12), 1911, 1979. 

In addition to the desired dependence on AC, it has a matching-dependent offset and gain that depends on parasitics. Any deviation of the reference capacitor Cref from the nominal value of the sense capacitance Cs appears as offset. Since in many applications AC is much smaller than C0, this offset often exceeds the signal. Offset cancellation should therefore occur early to minimize the dynamic range of the readout electronics. Care should also be taken for the trimming not to introduce a poor temperature coefficient. One solution fabricates the reference with the same process and in close proximity to the sense capacitor. The z axis accelerometer shown in Fig. 6.1.3 [7] utilizes two rnicromachined structures for the sense and reference. The suspension of the reference structure has been made intentionally stiff. 

For optimum noise performance the bandwidth of a sensor and its evaluation electronics should be limited to a value no larger than that required by the application. For example, an accelerometer with a noise floor of 1 mG (1 G = 9.8 m/s2) in a 1 kHz bandwidth will resolve 500 pG when its bandwidth is reduced to 250 Hz. Further bandwidth reduction results in additional improvement up to the point where a different noise source dominates (e.g., flicker noise). 

Most silicon accelerometers are based on a micromachined variable capacitance element (g-cell) that is converted to a voltage using a C-V converter and then amplified, filtered, and buffered to provide an analog output as shown in Fig. 7.1.4. To date, open-loop implementations for capacitive read-out circuits are more widely employed than closed-loop systems, primarily as a result of the stability of such systems [16]. Interface electronics for micromachined sensors depend not only upon the transduction technique (input specification) and the product requirements (output specification) but also on the packaging approach, as parasit-ics are introduced when a multiple-die packaging technique is used. 

Microelectromechanical systems (MEMS) combine the electronics of microchips with micromechanical features and microfluidics to create unique devices. The multitude of MEMS applications continues to grow including many types of accelerometers, radio frequency (RF) devices, variable capacitors, strain and pressure sensors, deformable micromirrors for image projection systems, vibrating micro-membranes for acoustic devices, ultrasound probes, micro-optical electromechanical systems (MOEMS) and MEMS gyroscopes, to name a few. 

Gross motor coordination can be assessed with standard clinical neurological tests, such as finger-to-nose, one-leg stand, and observation of gait, and by computerized body sway devices. Tremor can be assessed by observation using standardized rating scales, or with electronic devices (accelerometers). 

Colored pigments or fluorescent UV indicators may be used to inspect for bleedout from adhesives during and after cure. They may also be used to inspect for particles of cured adhesives that may have detached, migrated and contaminated other parts of an electronic assembly. Particles of electrically conductive or nonconductive adhesives can cause failures in microelectronic assembhes, gyros, accelerometers, or other electromechanical systems and are especially serious in space electronics. Rhodamine B which is pink to red in both the visible and UV regions and 2,6-distyrylpyridine which is visually colorless but intensely blue in the UV region are effective indicators in some adhesives formulations. 

Table 8.3 provides a summary of various types of sensors used for defining movement and impact. While a number of different sensors and electronic devices can be used, it seems that accelerometers and strain sensors are the most popular for sensorised garments. 

Smartex Wearable Wellness System Smartex s.r.l. Bra, shirt Cardiac data, respiratory, body posture and movement (accelerometers), estimation of energy expenditure, steps/min Electronic device contains accelerometers and is inserted into a front pocket at chest (Smartex s.r.l., 2014h)... 

To get further independent information about the oscillations of the building an additional accelerometer was installed on the abutment as a sensor on the object. The double integrated accelerations of the abutment, produced by the retarding train, over the time, also represent the oscillations and movements of the abutment. Finally an interpretation in a joint model will be shown, which combines the heterogeneous data of the electronic camera and the accelerometer. 

Nevertheless the measured accelerations during a brake test show, that we can get information of movements of the abutment in addition to the measurements of the electronic camera (Fig. 8). More distinctly than in the measurements of the electronic camera we can see the train driving onto the bridge, the start point of the braking and the oscillation of the abutment during the stopping of the train. We will use this information from the accelerometer to interpret the geometrical measurements of the electronic camera. 

INTERPRETATION OF THE MEASUREMENTS WITH ELECTRONIC CAMERA AND ACCELEROMETER IN A JOINT MODEL... 

Figures 6 and 8 show the pure, but calibrated measurements of the electronic camera and the accelerometer on the abutment. This data is superimposed by a noise. The noisebandwidth before the beginning of the braking is representing the variance of the observations. The problem which we have to solve is to determine the movements of the abutment in the direction of the brakepower, which is the direction of the bridge axis, by using the observations of the electronic camera and of the accelerometer. To achieve this we have to treat both data in a joint model with the performance function S t).

A different way to manipulate the heterogeneous data of the electronic camera and of the accelerometer in a joint model is possible, if we consider the horizontal movements of the abutment as a dynamic process. Then we can estimate the state of the system for each moment within the measuring time from all measurements in advance by using a Kalman Filter (Schrick 1977). In addition to the measurements for a Kalman Filter we need a priori knowledge of the dynamic system, start values and characteristic quantities of the system error and measuring error. I will give only a short summary of the nesessary algorithm here, whereby the dynamic system is not forced. 

Observations are the way s t) from the measurements of the electronic camera and the accelerations s t) from measurements of the accelerometer and the observation equations are... 

Currently plastics represent around 13% of the total weight of a medium-sized car and industry experts believe that 90% of future car design improvements and innovations will have an electronic content such as electronic tyre pressure monitors installed to improved road safety. The ultimate tyre pressure monitor has been fitted to the world s fastest road car, the Bugatti Veyron 16.4. Its wheel electronics comprise a military grade battery, absolute pressure sensor, temperature sensor, accelerometer micro-controller and radio transmitter/receiver which are housed in a compact wheel housing made from PEEK. 

In the following, the fabrication and characterization of micromachined high frequency focused polymer ultrasonic transducers in a manner that is compatible with CMOS microelectronics, and MEMS batch fabrication techniques, are described. The specifics of the electronics are not described here, but the interested reader may find more details elsewhere [75, 76, 81-84]. The transducer is capable of being manufactured on silicon wafers after the completion of CMOS electronics. These two key elements enable the eventual creation of a monolithic transducer chip that does not require modification of the standard circuit fabrication process. This type of transducer chip will likely follow the path of other MEMS devices such as accelerometers, gene chips and digital micromirror arrays, where batch production, high yields and... 

The outer garments should provide the necessary ballistic protection and could accommodate a different set of sensors and other electronic components, including temperature sensors, accelerometers, a GPS module and a textile antenna. The sensors and electronics needed for monitoring the environment should be fitted into the outer... 

Figure 1 shows an eZ430-Chronos sport watch, a product of Texas Instrument which has been widely used in various wireless applications.Zhou Z. [6] has developed the watch to be used as an electronic door locking device [6]. The watch was programmed to communicate wirelessly with the device attached to the door for the door to be locked and unlocked. This is done by tapping on the watch s 3-axis-accelerometer which is located on the watch s liquid crystal display (LCD). Thisproves that the wireless communication of the watch can be developed as long as the RF transceiver used is suitable for low power wireless applications. 

---