Sensor calibration

All sensors require calibration, which can be very elaborate in some instances. In addition to the usual primary calibration methods imdertaken in the ashore laboratory or testing center, less rigorous calibration is required aboard the vessel used for offshore geotechnical site investigations. 

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The data received should first be corrected for sensing errors. This usually consists of sensor calibration correction. 

The most common reference points for temperature sensor calibration are the freezing and boiling points of water. The freezing point is a function of the purity of the water-ice system. When both pure ice and pure liquid water are present, the ice is melting and the temperature of a well-stirred mixture is, by definition, 0°C. It is the most accurate calibration point for that reason. If it is possible to use such a quantity in a calibration, then the calibration is true and without question. 

For thermal characterization and temperature sensor calibration a microhotplate was fabricated, which is identical to that on the monoHthic sensor chips, but does not include any electronics. The functional elements of this microhotplate are connected to bonding pads and not wired up to any circuitry, so that the direct access to the hotplate components without electronics interference is ensured. The assessment of characteristic microhotplate properties, such as the thermal resistance of the microhotplate and its thermal time constant, were carried out with these discrete microhotplates. 

The sensor is based on high affinity of gold to mercury and on chemo-resistive properties of ultrathin gold layers adsorption of mercury leads to increase in the surface resistance [1,2]. However, this effect is not selective similar changes are caused by adsorption of water vapor and sulfuric compounds. The use of monomolecular layer of alkylthiols as a filter excludes this interference completely [3]. Sensor calibration is performed by thermoinjection of nanogram-amount of mercury quantitatively deposited by electrochemical reduction [4],... 

USE OF OXYGEN SENSORS AS A SURROGATE GLUCOSE SENSOR FOR IN VIVO TESTING AND IMPORTANT ISSUES RELATED TO IN VITRO SENSOR CALIBRATION... 

Figure 4. Chlorine sensor calibration curves at E = 50 mV for two different...

For instrumentation without a built-in sensor, calibration can be performed manually using a UV filter radiometer, luxmeter, thermopile or chemical actinometer (18-20). 

The uncertainty of commercial calibration gas mixtures is typically 1% of the amount fraction, and the contribution of this to the overall measurement uncertainty is much greater than the intrinsic error of the oxygen sensor for amount fractions of oxygen that are 0.1 ppm and above [2]. Consequently, test procedures that require calibrated gas mixtures will be limited by the uncertainty of those gas mixtures, and therefore carmot be used to test the accuracy of oxygen and other zirconia-based gas sensors, assuming the uncertainty of the sensor calibration is no worse than that of the test mixtures. At present, the uncertainty of commercial calibration gas mixtures is a limitation to verifying the accuracy of these gas sensors. 

Each weight current is active by default and can be deactivated during sensor calibration by zapping of the specific thyristor (Fig. 6.2.10). The remaining active cur-... 

Zero-order sensor calibration (individual sensors)... 

This chapter primarily deals with the issue of correlation between sensor signal and analyte concentration in chemical measurements, i.e. the creation of a model based on standards, and the estimation of unknown samples based on that model. Sensor calibration is dependent upon the type of sensor signal such as linear versus non-linear response and sensor format involving one or many sensors simultaneously. The advantages of moving from one sensor to several sensors and from several sensors to several sensors coupled with analyte concentration modulation can yield remarkable information about a sample [1]. Each level of sensor system complexity, when coupled with the proper analysis tools, creates an unique situation which yields information about each component in a mixture and potential interferences. 

ZERO-ORDER SENSOR CALIBRATION (INDIVIDUAL SENSORS)... 

This excitement about second-order sensor calibration has led to a search by chemometric researchers to find equivalent instrumentation that gives rise to second-order data. The definition of second-order instruments is slowly solidifying and currently a foundation has been established to classify which techniques are true second-order devices. This definition of second-order instruments is simply two sensor arrays which are independent of each other. However, in order for the arrays to be independent, one of the arrays must modulate the sample s analyte concentrations. The best known instrument... 

The sensor response to a given value of the measurand can be predicted by the sensor transfer function F, Y = F(X) determined from a theoretical sensor model or a sensor calibration. However, the value of the measurand determined by the sensor X easured differs from the true value of the measurand Xtrue ... 

Sensor linearity may concern primary measurand (concentration of analyte) or refractive index and defines the extent to which the relationship between the measurand and sensor output is linear over the working range. Linearity is usually specified in terms of the maximum deviation from a hn-ear transfer function over the specified dynamic range, hi general, sensors with linear transfer functions are desirable as they require fewer calibration points to produce an accurate sensor calibration. However, response of SPR biosensors is usually a non-linear function of the analyte concentration and therefore calibration needs to be carefully considered. 

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