Sensor single-shot

The accuracy of MWD directional measurements is generally much better than the single- or multishot-type measurements since the sensors are more advanced and the measurements more numerous. The azimuth measurement is made with the three components of the earth magnetic field vector and only with the horizontal component in the case of the single shot or multishot. The accelerometer measurements of the inclination are also more accurate whatever the value of the inclination. The average error in the horizontal position varies from... 

Another approach is the use of the potentiometric principle with planar thin film electrodes on a separate chip but in close vicinity to a FET input amplifier. Glucose and urea chips are now on the market commercialized by the company i-stat. These sensors are based on ion selective electrodes. The problems of stability are circumvented by a simple on chip calibration procedure and by the use of such microelectronic electrodes as disposable single shot probes for measuring Na, K, Cl, BUN, Glucose,iCa,pH,pC02 and Hct [56,57]. 

To overcome immobilization of biological substances and to establish diffusion limitation a number of methods have been tried. For example in the mediated disposable glucose sensor screen printing of free enzymes and mediator have been used. Due to the solubility of both substances only single shot apphcations are possible. For long term applications more sophisticated methods are necessary. 

The most obvious mechanism by which the analyte may modify the molecular structure of the probe is the formation of an analyte-probe complex. The analyte may bind to the probe by either physical or chemical bonding. For reversible sensing ffie binding interaction should be completely reversible, otherwise the probe will be suitable only for single-shot measurements. Knowledge of the binding equilibria is critical when designing sensors based on this type of probe. 

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