Sensors and pressure. Pressure is the force exercised on a surface, object or person. Pressure can be exercised by liquids, gasses and solids as well as by persons. In this case, it is possible for sensors to be in an industrial places with pressurous environments. Pressure-resistant sensors are suited for this.
Pressure is often expressed in pascal (Pa) next to other known units such as bar and atmosphere.
The total pressure strength is exercised on a surface is divided over this surface. That is why this pressure is described as the strength per surface-unit that is exercised.
What are the types of pressure?
There are four types of pressure: Absolute pressure, air pressure, underpressure and overpressure. A fifth alternative situation is a vacuum, also known as airlessness. Below these types are further explained.
Absolute pressure is measured (partly) independent of other reference values. The value that is recognized to this pressure is in relation to the zero mark of pressure: a vacuum, which is addressed later. Often, the absolute pressure is the present pressure in an environment.
This is the present pressure in the atmosphere (sky) in a room or area. The sky as we know it is filled with various types of gasses, each exercising a certain pressure. This pressure arises on the one hand because of the gravity and on the other hand due to the height of the air column which exists above this layer of air.
Underpressure and overpressure
These are the relative pressure measurements which are expressed relative to the air pressure. It can happen that, for a specific application, another pressure as reference value is used, but this is an exceptional case. Underpressure is a pressure measured lower than the air pressure. This one is noted with a negative number, -2 mbar for example. Overpressure on the other hand is a measured pressure that is higher than the air pressure. This one is noted with a positive number, +3 mbar for example.
When an area does not include gasses and liquids and no pressure is present, this is a vacuum. Every other pressure is thus an overpressure if a vacuum is used as zero mark.
There are industrial processes in which the pressure in the environment can increase up to a high level. There have to be sensors which offer solutions for these environments as well. Sensors which can not handle this pressure are on the one hand not usuable for a long time and on the other hand not reliable, assuming they work at all. A selection of sensor solutions for use in pressurous environments are explained below:
Inductive proximity switches for pressurous environments
Inductive proximity switches are sensors which are used for detecting metal objects. The detection of metals is done by an electromagnetic field that is generated by the sensor.
In pressurous environments special pressure-resistant inductive proximity switches in a full (AISI 316L) stainless steel housing are used. The sensors can operate at the exposure of pressure up to 80 bar. This is ideal for various industrial applications: from a level or filling measurement in a silo with for example iron ores to positioning in a hydraulic cylinder.
Moreover, the inductive sensors are provided with an IP69K sealings class making the sensors splash-proof and no dust is getting in. If you would like to know more about proximity switches, this article could be interesting: The difference between inductive and capacitive sensors
Pressure-resistant ultrasonic sensors
Ultrasonic sensors are sensors that are used for measurements of level and distance as well as for detection. The sensors use a echo measurement of ultrasonic sound.
In environments with pressure, the special ultrasonic sensors are provided with AISI 326TI stainless steel housings and extra firm sealing rings arround the transducer. The hps+ serie of microsonic can manage an overpressure of 6 bar. Moreover, this sensor has a layer of teflon which makes it resistant to agressive substances. This way, it is ideal when exercising filling measurements in tanks with various liquids: from water to fuel and agressive acids.
To learn more about sensors and chemicals the next article could be useful:Chemical resistance and sensors.