【Weekly 3 Questions, Question 15】2017.09.12

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This post was last edited by xh8618 on 2017-9-12 08:19; by editing bg9.png, you can see the answers to the previous section (quiz questions). Why is it necessary to perform cold-junction compensation when using thermocouples for temperature measurement? The magnitude of the thermocouple’s electromotive force is related to the temperatures at its two ends. The temperature-electromotive force relationship curve is calibrated with the cold junction temperature set at 0°C. In practical applications, since the cold junction of the thermocouple is exposed to the surrounding environment, its temperature cannot remain constant at 0°C or fixed at any specific value. Since the electromotive force depends both on the temperature of the hot junction and that of the cold junction, any change in the cold junction temperature will inevitably lead to measurement errors. To eliminate such errors, cold junction compensation is necessary. The topic for this issue is as follows: (Calculation problem) A double-flange level gauge transmitter is used in a storage tank; the lower flange of the level gauge corresponds to the lower limit of the liquid level. The distance between this lower flange and another point is h1 = 0.5 m, as shown in the figure below. The density of the liquid being measured is ρ1 = 960 kg/m3, and the distance between the centers of the upper and lower flanges is h2 = 5 m. The calibration range of the level gauge is from -47 kPa to -3.8 kPa. Due to damage to the diaphragm, a new double-flange level gauge needs to be installed. The density of the filling fluid in the capillaries of this new gauge is ρ3 = 1060 kg/m3. What is the calibration range of the level transmitter after the replacement? (g=10m/s2) file:///C:\Users\ADMINI~1\AppData\Local\Temp\ksohtml\wps48F7.tmp.jpg