Mass Flow Indicator

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Mass flow rate of liquid is an important parameter to be measured and controlled in a process industry. In the present paper, the design of a PC based mass flow indicator has been studied using a well known temperature sensing IC AD590. The temperature sensing IC AD590 has been used as a flow sensing element and the effect of fluid temperature has been eliminated by using four identical IC units. Four IC units are connected in the differential mode. The output of the differential circuit is send to optoisolator circuit through a signal conditioner circuit. The output of the optoisolator circuit has been displayed in a PC monitor using Labtech Note Book Pro software. A theoretical equation relating the output of this circuit with flow rate…show more content…
In this technique the anemometer effect i.e. cooling effect of flowing fluid on the heat sink metallic surface of a temperature sensing IC unit like AD590 is utilized to measure the mass flow rate of the fluid. In order to compensate the temperature effect of the fluid, four identical IC units are used and mounted in the same diametrical plane along two perpendicular diametrical directions. The flow tube is mounted in the horizontal position in such a way that it is always filled up with flowing fluid. Four identical temperature sensing units (AD590) are mounted at equidistance apart in the same diametrical plane of the flow tube, of which two sensing IC's are mounted along a horizontal diameter and the other two IC's are mounted along the vertical diameter in the same plane. As a result the cooling effect of the fluid on the IC's along horizontal diametrical positions may be assumed to be different from that on the IC's along vertical diametrical position. All the IC units are supplied from the same stabilized 5 Volts dc source so that their heat supply rate is identical. The output of each IC is a current signal passing through a load resistance and is not dependent on the value of load resistance up to a certain limiting value. The dc voltage developed across each load resistance has been found to be related with fluid flow rate. Sum of the voltage signals developed for two horizontal IC's has been subtracted from that of the voltage signals for two vertical IC's. As a result the effect of temperature of the fluid is nullified and the resultant after this subtraction may be assumed to be a function of fluid flow rate only. The dc voltage developed in the differential op amp is of the order of mV signal. This signal is converted into 1-5 volt signal using instrumentation amplifier and signal conditioning circuit. This 1-5 volts signal is send

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