Pressure is a very important physical phenomenon in different kinds of areas such as engineering. We need to measure it in lots of kinds of situations to implement the solutions. In some cases, we want the pressure high and also sometimes low. But, we can understand it with pressure measurement devices. Here, you will find detailed information about these devices. You can find detailed information here about these topics;
- What are the pressure measuring devices?
- Types of them,
- What is pressure?
- Calibration of the devices.
What are the Pressure Measurement Devices?
Throughout history, people developed different kinds of instruments to measure pressure in different kinds of situations. Because pressure is not only taking place in the atmosphere. For example, meteorologists are measuring the pressure of the open air to guess the rains and other weather forecasts.
Also for design engineers, it is very important to measure the total fluid pressure on the surfaces of the parts inside the fluid. So, different aspects of this natural phenomenon are very important for different fields. Because of this reason, there are different kinds of devices to measure the different kinds of pressure.
Among the different types, these are the most common instruments;
- Bourdon tubes,
- Pressure transducers,
- Strain-gage pressure transducers,
- Piezoelectric transducers,
- Deadweight testers.
We use the barometer the measuring atmospheric pressure. Atmospheric pressure is a very important phenomenon that affects different kinds of things.
As we stated above, atmospheric pressure is very important for weather forecasts. And also, it is very important for the working of the different types of machinery. At higher elevations, the working of internal combustion engines changes. Because the total air and oxygen that it takes into the cylinders change. We need to make some sorts of calibrations to these engines to work in higher elevations.
Before the use of the barometers, a scientist who is Evangelista Toricelli made an experiment to measure the pressure of the atmosphere. In a container filled with pure mercury, he immersed an open-end tube from the open end. And the mercury rise inside the tube. This rise is because of the atmosğheric pressure that is applied on the surface of the mercury in the container. And the closed end of the tube is the vacuum.
Calculating the Pressure
So, the mercury rise around 760 millimeters in that tube. We can calculate this pressure with this formula;
Here, ρ is the density of the fluid that we use in the experiment. And the g is the gravitational acceleration, and h is the rise of the fluid in the tube.
As you understand from this equation, with the increasing density values, the total height of the rise of the fluid decreases. For example, with Mercury, this rise is 76 cm. But with the water, it will be above 10 meters.
Because of this reason, we call 1 atm pressure 760 mmHg at 0°C and sea level. This is the absolute reference point for our measurements. Also, because of the Toricelli, we call the 1 torr pressure 760 mmHg which is also equal to the 133.3 Pa.
We stated that with higher elevations, the atmospheric pressure drops. Because of this drop, the cooking takes longer times. Because the water boils at lower temperatures in higher elevations.
Also, if you are a runner, you will see that you will get tired more in higher elevations. Because the density of the air decreases and the total oxygen that you take into your lungs will decrease. But if you go on to the exercises, your lungs will be more strong to get used to these conditions.
Manometers are also very useful devices to measure the pressures of tanks and gases. They are very important in such engineering applications where pressurized gases are used. They use the same principle with the barometers.
The general working principle of the manometers, they have a U tube that is filled with liquid. This liquid can be alcohol, water or mercury. One side of the tube is attachable to a tank. And the other side is open to the atmosphere. So, according to the atmosphere, you can measure the absolute pressure of the pressure tanks.
Manometers are the best for the measurement of little to middle-pressure differences. If they use fewer densities of fluids, the pressure measurements will be more accurate.
We can use this equation to calculate the total pressure difference between the air and the ğressureized tanks;
As you see above, the same logic is valid for manometers. We need to add the total fluid rise effect on the U tube to the atmospheric pressure to find out the tank pressure.
In the design of the manometers, it is very important to avoid the capillary effect of the fluids in tubes. So, we need to select a proper diameter for the tubes so that the capillary effects of the fluids are negligible.
Also to increase the accuracy of the pressure measurement, the atmospheric side of the manometer devices can be produced at a certain incline. This incline gives more accurate pressure measurements.
These pressure measurement devices are also very important. We use them in the measurement of the pressure differences in the fluid flow sections. For example, think about a fluid flow in a pipe. And we need to know the pressure drop in a pipe section. So, we attach a differential manometer between two points that we want to measure the pressure differences.
In this differential manometer, the two edges of the U tube is attached to these point of this fluid flow. So, there is a pressure measurement fluid that is not mixed with the flowing fluid. And the height difference of this pressure difference will give us the total pressure difference.
This is also a very important type of pressure measurement instrument. Bourdon tubes are using mechanical principles to measure the pressures of the environment. And also, reading pressures are very simple with these devices.
If we take a look at the general working principle of the bourdon tube, there are metal spirals and coils that deflect with the application of pressure. This pressure application is at the open side of the tube. And there is a liquid on that side. This liquid applies pressure on the coil because of the outside pressure, and this coil deflects.
Also, there is a dial indicator at the other end of the coil that measures the total deflection. So, a bourdon tube is calibrated to measure the pressure with these deflections.
The most important advantage of the Bourdon tubes, we can use these pressure measurement devices in the measurement of different things. Such as atmospheric pressures and pressure of a gas in a tank.
Accurate calibrations can be a problem for Bourdon tubes. Because, it depends on the mechanical system and the deflections of metals. In higher temperatures, the metal can expand, and this can lead to a problem in the reading correct and accurate values.
Electronic systems become more reliable if we compare them with mechanical systems in pressure measurement. They can able to measure the pressures on a more accurate and more wide range basis. So, in general, electronic systems are very common in more professional pressure measurement applications.
One of these electronic pressure measurement devices is the transducer. They are transforming the effect of pressures into voltage, resistance, and capacitance changes. So in general, they are not affected by external conditions.
Gage Pressure Transducers
There are different kinds of pressure transducers available in the market. These transducers are using different kinds of pressure measurement methods. One of these pressure transducers is the gauge pressure transducer.
The diaphragm of these devices is directly looking at the atmosphere. So, the reference point of the pressure measurement for these devices is the atmospheric pressure. On the screen of this instrument, you will see no pressure, because it assumes that atmospheric pressure is 0.
Absolute Pressure Transducers
These are the electronic pressure measurement devices that are calibrated to measure the full vacuum as 0 pressure. So, the atmospheric pressure is not a reference point for these applications.
Differential Pressure Transducers
The working principle of these devices is the same as the differential manometers. We use these electronic pressure measurement devices in the measurement of the pressure difference between two environments.
Strain-Gage Pressure Transducers
This is also a very different electronic pressure measurement device. In strain-gage pressure transducers, there is a diaphragm that one side of it opens to the pressure measurement. When there is pressure applied to this side, the diaphragm stretches. And there is a Wheatstone circuit beside this diaphragm. The output of this circuit amplifies with the strengthening diagram. So, the measurement takes place electronically.
Piezoelectric Pressure Transducers
Also, this electronic pressure measurement device has a very different working principle. There is a crystalline substance that produces electrical potential with the application of mechanical pressure. So, measurement takes place according to this principle. You can read the pressures from the screen of the device. Because the device converts this potential to the readable pressure values on the screen.
The advantage of the piezoelectric pressure transducers is, that they are very good in the rapid measurements of high pressures.
For Calibration of Pressure Measurement Devices: Deadweight Tester
Calibration is a very important thing in the measurement in engineering and professional areas. So, we need to calibrate the devices that we use in different measurement systems. Also, pressure measurement devices have a calibration technique. And in general, deadweight testers are used in the calibration of them.
Deadweight testers have a principle that is same as the Pascal’s Law. So, the pressure application is exact in mechanical means, and we know the applied pressure directly. There are piston and liquid systems to apply the known pressure on the devices. So, calibration takes place for these pressure measurement devices.
We need to make the calibrations in regular intervals to these pressure measurement devices to obtain good results.
What is Pressure in Pressure Measuring Devices?
We talked about pressure measurement and the different techniques that we use in the area. But, we do not know exactly what is the pressure.
In most fundamentals, pressure is the total load in a unit area. So, we measure the pressure with load and the area of the application of that load. This load is generally the force. According to that, we can state the unit of the pressure is Newton/Area in SI units which is also Pascals. Also in English units, it is pounds/square inch which is also PSI.
This is the general statement about the pressure. Also, we need to know the general pressure units to read the pressure measuring devices. Because they are showing the values in different units.
For example, 1 atm pressure is equal to the 101.325 Pascals and also 14.7 psi. A pressure measurement device can say that the pressure is 2.5 atm. We need to understand that, 253.3125 Pascals or 36.75 psi.
Also, pressure measurement devices can give results in mmHg. So, 1 mmHg is equal to the 0.00131579 atm pressure. So, 0.1333 Pa or 0.019 psi. According to this calculation, if a pressure measurement device states that the pressure is 150 mmHg, we need to understand that the pressure is 19.95 Pascals or 2.85 psi.
It is very important to know these units related to pressure.
Pascal’s Law on Pressure Measurement Devices
It is a very important law about the pressure on liquids. It is about the abilities of liquids to transmit the pressure through themselves without any loss. So, we use this principle in different kinds of hydraulic systems applications.
According to Pascal’s Law, the amount of the pressure does not change at the other portions of the fluid, if we apply pressure from a section of the fluid. To clarify it, think about hydraulic lifters. The pressure is the F/A. We are applying force to an area of fluid. So, the pressure value is the same as the other piston that has a bigger area. So, the force will be smaller in this area.
And also, if we apply a force to a bigger piston area, the force will be much bigger in the smaller piston area section. This is the general working principle of hydraulic systems. Also, we use Pascal’s law in the calibration of the pressure measurement devices.
Conclusion on the Pressure Measuring Devices
So, there are lots of kinds of these devices. And the working principles of these devices are very different from each other. You can select the best one according to your application. There are mechanical ones and electronic ones. You must choose between them to apply to your applications.
Also, it is very important to which scale of pressure you will measure. Because the general devices are working in different conditions and also under different pressures that we measure. For example, you can measure very high values of pressure with electronic pressure measurement devices. But also, barometers are very good at measuring atmospheric pressures.
Before using the pressure measurement devices, you need to understand what the pressure is. It is very important to know the units and meaning of the pressure in different unit systems such as English units and SI units. Also, you need to be able to make conversions between different units effectively. Because different devices will show the values in different units.
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FAQs About Pressure Measurement Devices
Different devices work in different ways. But the most important distinction is whether they are electronic or mechanical. Around the mechanical devices; barometers, manometers, bourdon tubes. Also, there are electronic devices that are generally transducers. They are; gage pressure transducers, absolute pressure transducers, differential pressure transducers, strain-gage pressure transducers, and piezoelectric transducers.
Pressure is a very important value that we consider in different ways. Also in measuring this physical phenomenon, there are 3 approaches. These approaches are; absolute measurement, gauge measurement, and differential measurement. Absolute one takes the references as the complete vacuum. Gauge measurement takes the reference as atmospheric pressure and differential are about the pressure differences between two environments.
These devices above are made for direct measurements. For example, you can use a piezoelectric transducer to directly measure the pressure of an environment. Because it gives a direct result of pressure.
There are different kinds of measurement methods. Around these methods, there are mechanical and electronic ones. In mechanical systems, generally mechanical effects of the pressures are used. For example in barometers, the effect of the pressure on the liquid is used to measure the atmosphere. Also in electronic devices, we use transducers to transform the effects of pressure into electrical things.