What is a Pressure Sensor?
The sensing of pressure is an integral part of controlling processes in many different industries. For example: building automation; transportation; and manufacturing are but a few industries where calculating pressure data is a key step in achieving an end product. So what exactly are these instruments that do all of this important data collection in so many different processes? Let’s examine what a pressure sensor is, how it works, and a couple of examples of how we use them throughout industries today.
What is a Pressure Sensor?
A pressure sensor is a catch-all term for some sort of instrument that measures pressure. The wording is deliberately generic as there are many different styles of sensors. These sensors can measure the pressure relative to a few different standards.
Strain-gauge sensors were the first type of electrical instrument constructed to measure pressure. Also known as a strain-gage; these sensors are typically made of a micron-thin wire coil of constantan sandwiched between two insulating layers. You might remember constantan, an alloy of copper and nickel, from our discussion on thermocouples. When pressure is applied the strain-gauge deforms; elongating the shape of the constantan coil, and increasing the resistance. Alternately, if a pressure force is removed; the coil will become more compact and cause a decrease in resistance of the wire. Thus, incredibly small physical changes translate into measurable electrical signals that can be related to a respective amount of pressure.
Figure 1: Strain-gauge
Another type of pressure sensor can work due to the piezoelectric effect. Some materials, when put under stress, exhibit an electrical charge. In the case of measuring pressure, the stress is exerted through the process pressure. Which in turn, causes a voltage that correlates to a respective pressure. The piezoelectric effect may be more familiar to you from its use as an ignitor for gas barbecues or stovetops. In these cases, a spring-loaded hammer strikes quartz to produce a voltage. However, instead of the voltage being read as a measurement of pressure, it is used to generate the ignition spark. Other devices that also use this effect range from acoustic microphones to forms of radar.
Here at Enercorp, our differential pressure transmitters operate based on the deformation of a ceramic membrane, a type of strain-gauge. The amount of the deformation is converted into an analog signal and transmitted to a process controller. Curious as to what these instruments are actually like? Have a look at our PX61 Pressure Transmitters to see a type of the actual sensor we have been discussing.
Figure 2: Enercorp’s PX61 version of pressure transmitter
What is a Pressure Transducer?
Transducing is the act of quantifying a physical force into an electrical signal. In the case of our pressure sensor, it is taking a physical measurement of the pressure. Which it then converts into an electrical signal. This means that technically our pressure sensor can be more accurately described as a pressure transducer. This translation of the physical pressure measurement is key to process controls and automation. The computers and controllers that will use the pressure data don’t understand PSI, millibars, or kPa. They do, however, speak in the language of electricity. Therefore, 0ur pressure transducer helps act as the interpreter between those different “languages.”
What is a Pressure Transmitter?
The last job of our pressure sensor is to send that electrical signal on to a process control. Where it can be displayed or acted upon. Since the act of sending a signal is called transmitting. Then our pressure sensor is also, technically, a pressure transmitter. It takes a pressure measurement that has been transduced; and sends that data off in the form of an electrical signal. Additionally, the transmitted signal can be one of many different types; too many to discuss in this blog. If the specifics of these signals intrigues you, be sure to head on over to “What is an Analog Signal?” where we go over the basics behind this important process control information stream.
What uses a Pressure Sensor?
There is much more to pressure than meets the eye, or rather, the eardrum. Pressure sensors can have fairly obvious usages; for example, measuring tire pressure for vehicles or barometric pressure for weather stations. But in the same way that tire pressure is sensed; one could also measure the amount of liquid or gas in a tank. And just like sensing the local air pressure to determine weather forecasts; you can tell the altitude of an aircraft in flight with barometric pressure. A pressure sensor can measure, variables such as the amount of liquid or gas flowing through a pipe.
At Enercorp we sell the VIP-9000. This instrument works like a pressure sensor, but backwards. It converts more modern 4…20mA or 2…10mVDC signals into 3…15psi, a legacy pressure-based standard. The VIP-9000 acts as a stop-gap measure for older, automated infrastructure that needs to talk to newer process control systems.
Figure 3: Enercorp’s VIP-9000
A pressure sensor can do much more than just sense the data of a variable. Sure, it could simply relay data to a central processing centre; but it could also directly trigger actions as a response to the measurement of certain parameters. For example, a valve that allows water to flow could be closed when high pressure reaches a certain threshold. Alternatively, let’s say some gas was leaking from a storage tank. A pressure valve could sense an abnormal lowering of pressure and trigger the sounding of an alarm. The transmissions from the pressure sensors can bypass any central processing and act as an independent system.
To take a physical pressure measurement and end up with a type of useful data does require many steps. In short, whether you call it a pressure sensor; transducer; or transmitter; it doesn’t really matter unless you want to get overly technical. The important part is to understand a little about the tools we have to sense pressure; how they convert and transmit that measurement; and how we use that information to help run the many processes occurring all around us in our modern world. If you want to broaden your knowledge about pressure in general, be sure to read through our primer on pressure. If you want to narrow the scope down on pressure sensors instead, head on over to our blog on differential pressure transmitters for a more in-depth piece on one of Enercorp’s most popular products.