Electronic measuring instruments are commonly used to measure and display a wide variety of parameters, such as voltages, temperature, pressure, speed, frequency, acceleration, sound intensity, and illumination levels, to name a few. Such measuring instruments commonly include a sensor which generates an analog signal having a magnitude which varies in accordance with variations in the parameter being measured. While such analog signals can be used to directly drive analog display meters, it is now common to convert the analog signal, using an analog-to-digital converter, into a digital signal which can be displayed digitally on a display panel. An engineer or technician who is required to measure a variety of different parameters such as those listed above ordinarily requires a corresponding number of measuring instruments. However, the cost of maintaining a separate measuring instrument for each type of parameter to be measured can be significant. Many electronic measuring instruments in current use include a gain amplifier positioned between the sensor and the analog-to-digital converter.
For use with some sensors, the gain amplifier must be calibrated for zero signal strength (offset adjustment) and for full-scale signal strength (gain adjustment) in order to achieve reliable measurements or reading. Most electronic measuring instruments must be recalibrated periodically in order to assure accurate measurements. A calibration laboratory normally maintains a log of the date on which each measuring instrument was last calibrated, and the date on which the next calibration is due. Unless the calibration log is reviewed on a schedule, it may happen that an instrument will continue to be used beyond its scheduled recalibration date, which results in readings which may be in error. Also, particular types of sensing elements can produce electrical signals representing the measured parameter, which electrical signals vary in different ways for a given change in the parameter being measured. For example, a temperature sensitive element might produce an electrical voltage that varies linearly with changes in the temperature being measured. By contrast, a pressure sensitive element might generate its signal in the form of an electrical resistance which ideally varies in accordance with a quadratic formula. Accordingly, for a measuring meter designed to be used with different types of sensors, it is necessary to know the type of sensor which is in use at any particular time in order to determine the best algorithm for computing the measured value. This requirement, however, limits the possibility of use of new types of sensors or detectors with a meter which does not recognize the sensor.
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