In your opinion, what are the primary limitations to the accuracy of outdoor air-temperature sensors, and...

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Physics

In your opinion, what are the primary limitations to theaccuracy of outdoor air-temperature sensors, and what could be doneto reduce these limitations?

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The Causes of calibration failure 1 Selfheating in thermistors and PRTs When thermistors and PRTs are calibrated a nominal excitation current is applied The amount of current thats required is generally stated on the calibration report or manufacturers specifications We learn from Ohms Law that when a current flows through a resistor power is dissipated I2R This power causes the sensor to heat which is known as selfheating When the temperature sensor is calibrated its selfheating has been accounted for When using either sensor type be sure to set the readout for the proper excitation current Too little or too much current will cause measurement errors These sensors can even be damaged if too much current is applied Some readouts will automatically choose the proper current when either thermistor or PRT is selected Others may need to be set manually The settings are generally in the probe setup menu If you select the current manually always refer to the thermometers specifications or calibration report for the proper current 2 Low insulation resistance and leakage currents Low insulation resistance is sometimes referred to as shunt resistance because current is allowed to flow outside of the measurement circuit Electrically it is like putting another resistance in parallel with the sensor When low insulation resistance occurs too often the transition junction temperature has become too hot The hub should not be so hot that it is painful to touch Additionally low insulation resistance may result if the sheath has been bent or if the seal has been compromised allowing moisture to reach the sensor and lead wires This problem usually can be avoided through proper use and handling 3 Transition junctions Thermistors and PRTs generally have transition junctions The transition junction is where the cable lead wires connect to See Answer

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