We see that machines rather than manpower are involved in almost all of today's industrial applications. Of course, since machines cannot think on their own like us, it is necessary to teach them what to do during the production phase with the right mechanics, electronics and software.
While creating these multi-component designs, one of the top priorities is to establish systems that will enable machines to feel, in other words, feel, just like we humans do.
So how do machines feel? For example, how does it understand temperature, pressure, velocity, acceleration, the position of its moving parts, or see an object we want it to see?
Of course, with SENSORS, which are developing at a tremendous speed with each passing day and which are getting smaller than we can see with the naked eye as the production technologies increase.
Without distracting the subject too much, I would like to explain the word "sensor" very briefly, as we have been taught since high school years. Sensors are elements that transform a physical quantity into an electrical signal.
After this short introduction, let's come to our main subject, which is the title of our article.
Which Pressure Transmitter should I choose?
As is known, pressure is the amount of vertical force acting on a surface per unit area. Solids, liquids and gases exert a force on the surface they are on due to their weight. Regardless of the source of the force, the force acting perpendicular to the unit surface is called pressure (P), and the force acting perpendicular to the whole surface is called pressure force (F). Pressure sensors are often required to monitor the pressure of liquids and gases in pressure sensitive environments. In addition, these sensors are transformed into a transmitter by adding electronic circuits to communicate with control systems, that is, to speak the common language and to give the desired output signal.
Let's choose our pressure transmitter for a few different applications.
First of all, I would like to state that we will make a choice over transmitters produced with strain gauges, which are used as the most common pressure measurement technique. The most common are transmitters that are mounted on a steel diaphragm or on a ceramic diaphragm and give us measurable values of voltage changes proportional to pressure, through a Wheatstone bridge (i.e., an electrical circuit that measures the change in electrical resistance). Another type of resistive pressure measurement is a piezo resistive sensor. The piezo-resistive microstructures are integrated on a semiconductor chip and encapsulated in an oil-filled chamber, which delivers pressure to the sensor through an external diaphragm.
At this point, our expectations come to the fore to choose among these sensors with similar operating principles.
Let's ask these questions and find the right product.
What is the application? So what are we going to use the sensor to measure the pressure of? Water, air, oil, steam, high viscosity liquids. We can increase the examples.
In which pressure range is it desired to measure?
What is the desired precision?
What is the desired output signal?
What is the mechanical connection type?
What is the electrical connection type?
What material should the sensor be made of?
What is the ambient temperature?
Let's try to answer all questions itemized.
Application: I would like to explain the application place by giving examples.
Air pressure measurement in the compressor: Compressors, whose pressure was measured with only one mechanical manometer in the past, are now much more technological. Pressures can be monitored and controlled instantly with pressure transmitters. Since very high precision is not required in compressor applications and clean air pressure will be measured, you can see your work even with the simplest transmitter. Here, pressure transmitter with ceramic diaphragm will be the solution.
Water pressure measurement in pump and booster: We can say that the booster system has become the standard in almost all new buildings. Again, since we will measure the mains water pressure, we do not need a very special sensor and high precision measurement, but there is such a point in the pump and booster system that this is the most annoying issue. During the first run of the pumps, the pressure can suddenly rise up to 4-5 times what it should normally be. Since standard pressure transmitters are usually resistant to high pressure up to 2 times, this instant high pressure can physically damage the transmitter. In other words, it causes the diaphragm to break or pierce, which means that the sensor becomes completely unusable. For this reason, products with steel diaphragm or silicon piezo type sensor can be preferred when choosing products for the pump and booster system. Ceramic diaphragm products deteriorate quickly due to their fine structure in these sudden pressure increases.
Hydraulic oil pressure measurement: The use of pressure transmitters is increasing in applications with hydraulic power units, mobile cranes, fire trucks and all other hydraulic systems. Especially when it comes to safety, it is a priority to control the pressure continuously and also to ensure the safe operation of the system. In such applications, it would be very appropriate to use steel diaphragm products in order to protect the transmitter against instant high pressure during the operation of hydraulic pumps, just like in water pumps. In addition, the presence of a pressure relief valve at the tip of the sensor provides extra protection and extends the life of the product. Some manufacturers have models that can withstand up to 5 times the pressure to be measured.
Pressure measurement in foods: In order to measure the pressure of fluid foods in a tank or line, pressure transmitters made of stainless steel, which are called flush diaphragms and whose end side can contact food, should be preferred. In other words, various food conformity certificates are sought in this type of pressure transmitters, which are called hygienic types.
Pressure measurement in marine applications: Pressure transmitters used in the marine and ship industry must also be made of materials such as stainless steels and titanium, which provide higher protection against the corrosive effects of the marine environment. Special certificates of many LOYD organizations are required for these pressure transmitters.
Pressure measurement in explosive atmospheres: Especially the petrochemical industry and pressure transmitters to be used in any explosive environment should not cause an explosion effect in the environment. These sensors, which are produced with special methods, must have an exproof certificate and their manufacturers are routinely inspected by the companies that give the certificate.
I wanted to give a few different application examples, but dozens of more different applications are emerging every day.
Pressure Range: The pressure at the point where the transmitter will be used should be known and the product should be preferred accordingly when choosing the product. When a product with a lower value is selected, the desired measurement cannot be made correctly and the sensor may be damaged. A higher value product can be selected, provided that it is close. The necessary calibration can be made and used. The only important point here is that the sensitivity will decrease a little. For example, a sensor with a maximum value of 400 bar can be used in a system up to 250 bar pressure. In addition, a type of transmitter I want to specify is also absolute working products. In general, autoclave applications are encountered.
Sensitivity: Product selection can be made according to the desired sensitivity in the pressure measurement. The cost of high-precision products in pressure transmitters is also quite high. This should be taken into account.
Output Signal: Products that will give appropriate signals to the inputs of PLC and other control devices should be selected. The most common transmitter output types are 4… 20mA and 0… 10V. Of course, there are products in different options such as ratiometric 0.5… 4.5V or optional 0… 20mA, 1… 5V, 1… 6V, 0… 5V for different processes.
Mechanical connection: The product should be selected according to the mechanical thread structure or flange type at the point where the transmitter will be connected. Some connection types are self-sealing, while others may require an additional o-ring. Some of the various connection types appear as G1 / 4, G1 / 2 or their NPT models.
Electrical Connection: These sensors are generally produced with direct cable outlet or socket. It can be selected according to the place to be used. In order to protect the sensor from dust or water that may come on it, attention should be paid to the IP protection class of the socket to be selected.
Body Material: The correct body material should be selected against the corrosive effects of the environment in which the product will be used and the material whose pressure will be measured. High strength stainless steels are generally preferred.
Ambient Temperature: The temperature of the material and the environment that the sensor will measure is one of the factors affecting the measurement accuracy. Product selection should be made according to the temperature values specified in the technical documents of the products.
With hundreds of different models of pressure transmitters available, users face a significant challenge.
Choosing a high-quality, feature-rich sensor when choosing the right product would be appropriate when budgets are large and the number of measurement points is low. Today's control systems have evolved further and while the need for more data from more measurement points has increased, budgets have not increased.
Marketers can only put forward the idea that a particular sensor model offers every advantage, but this is often used to hide the fact that the manufacturer only dominates one product and does not have products for others. Purchasing departments sometimes negotiate certain models to take advantage of volumes and purchasing power. There are many options, but those with technical backgrounds can understand the balance between price and value. You can basically spend different amounts for the same function. Choosing the cheapest option may cost you a lot more in the future, but expensive items may not always be the smartest option.
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