Most people are more familiar with – and often use – instruments for measuring pressure relative to the atmospheric pressure evident around us. However, some applications require absolute measurements, and this is where absolute pressure sensors come in.
Nevertheless, sensors are applicable only for gathering data. To make the system ready for analysis and practical use, you must pair the sensor with an absolute pressure transmitter. When you use it in conjunction with a transmitter, the data provided by the sensors become readable and easy to interpret.
However, it is also vital to remember that zero absolute pressure, or perfect vacuum, is impossible to achieve. As such, the calibration of absolute pressure sensors can still pose problems and continue to be challenging.
Despite this drawback, this excellent instrument prevails to be the best option if you want to get readings unaffected by changes in altitude or temperature.
What is an Absolute Pressure Sensor?
The measurement provided by an absolute pressure sensor is always relative to a zero pressure reference – with the reference value needing to be as close as possible to a vacuum.
A good analogy of this concept is with the use of Kelvin in measuring temperature. Zero degrees Kelvin is always a reference point for the coldest temperature possible. Therefore, pressure measurement of one bar in an absolute pressure sensor reading is always the reference point regardless of the temperature or altitude.
It would be best to use this type of pressure sensor for measuring the absolute value of pressure without the influence of other conditions such as atmospheric.
These sensors have a variety of applications, usually in the meteorological and aviation field. Some examples of applications using absolute pressure sensors include:
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Outdoor weather stations
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Semiconductor equipment
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Gas analysis systems
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HVAC/HVACR refrigeration systems
Both absolute pressure sensors and transmitters are essential in monitoring high-performance, industrial-grade vacuum pumps. They help in ensuring that the vacuum packaging of medical products is free from bacteria.
When it comes to the food industry, vacuum packaging is very common – especially since consumers are now more conscious of food safety. As a result, the vacuum packaging market continues to grow. And using absolute pressure instruments is one of the factors that contributed to the success of this particular industry.
How Does an Absolute Pressure Sensor Work?
Compared to gauge pressure instruments, the side of an absolute pressure sensor does not come into contact with the pressure media. Instead, it has exposure to a permanently sealed vacuum chamber. The deformation of a diaphragm allows electronic pressure sensors to get their readings. However, absolute pressure sensors are not dependent on this.
For example, a 10 psia (pounds per square inch absolute) will be 10 psi above a perfect vacuum. This value is equivalent to about 4.7 psi, below the standard atmospheric pressure of 14.7 psi at sea level. Therefore, a reading of 0 psia is the pressure of a perfect vacuum or the closest to it.
What are the Types of Absolute Pressure Transmitters?
An absolute pressure transmitter must have the same capability as the sensor – which means air pressure fluctuations and other external atmospheric changes should not affect it. They also do not need any connection with the external system, and as a result, they do not require a release or exhaust node.
Before you choose the best type of absolute pressure transmitter for your application, it is essential to know beforehand what each of them entails.
Absolute pressure transmitters come in three different types, but they all have the same working principle. They all convert the pressure relative to the vacuum into an electrical signal. The following are the various types to consider:
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Traditional mount:
Suitable for measuring gas, liquid, and steam pressure, a conventional mount absolute pressure transmitter comes with a single crystal resonant sensor. It is best to pick a model with features like quick response and remote monitoring when choosing this type. -
In-line mount:
This type also features a single crystal resonant sensor – perfect for measuring pressure on liquid, gas, and steam. It outputs a DC signal and features remote monitoring and setup through BRAIN or HART communications. The best models usually come with an optional status output for pressure alarm. -
High-performance in-line mount:
A superset of the in-line mount types, a high-performance model has all the features of an in-line mount. One of its capabilities worth noting is producing an output between 4 to 20 mA of DC signal, which corresponds to the measured pressure. It also has remote setup and monitoring using BRAIN or HART communication, diagnostics, quick response, and an optional status output for high/low alarm.
Techstar carries all of these types of absolute pressure transmitters. Some of their more popular models include EJA510E and EJX610A.
The Value of Using Absolute Pressure Transmitter
Different applications need their own set of instruments for measurements. Remember that you will need to have an absolute pressure transmitter if you require pressure measurement solutions without any influence from external conditions such as temperature or altitude.