The Foxboro pressure measuring system (Model IGP20) as shown in the following fi

Question

The Foxboro pressure measuring system (Model IGP20) as shown in the following figure is based on the strain gauge principle and has been set by the manufacturer to measure the pressure in the range of 20 kPa to 100 kPa. Describe with simple sketches how the pressure transmitter is installed in a pressure process. The following figure shows all components of the PC-based pressure measuring system using the above Foxboro pressure transmitter, a current to voltage converter and a DAQ card. What is the pressure to be measured if the reading in computer is 4 V (or 16 mA)?

Explanation / Answer

This kind of pressure easuring systems use Mathematical model employing following equations , we have:
P = SH
where
P = Pressure (Pa)
S = Weight density of the liquid (N/m3) = g
H = Height of liquid column (m)
= Density (kg/m3)
g = acceleration due to gravity (9.81 m/s2)
The level of liquid inside a tank can be determined from the pressure reading if the weight density of the liquid is constant.
These are installed on the base of vesel hence as soon as the level rises the pressure increases hence the output current is increased.
The output current is going from 4mA to 20mA for let's say the hight of vessel is 10m. Hance for each meater 0.625 mA current is transmitted.
In given case of 10m high vessel if the output is 16mA the level is at 7.5 m

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