Low pressure transmitters obviously measure low pressure. But did you know that there are three different types of pressures to measure? Different transmitters measure various types of pressures with varying degrees of accuracy. Know what you’re measuring before selecting the right transmitter to do the job.
Absolute Pressure
Absolute pressure is measured in relation to a vacuum. To do this, one would suction out all the pressure (both gauge and atmospheric) to leave only a vacuum. A specific transmitter would measure absolute pressure by determining the difference between the vacuum referenced and the pressure to be measured. This difference is considered the absolute pressure.
Differential Pressure
This is just as it sounds: the difference between two pressures. A differential pressure transmitter will determine two individual pressures and then measure or calculate the difference between those two. As one or the other changes in pressure, the difference will increase or decrease leaving you with a larger positive or negative differential pressure.
Differential pressure is a common measurement that often becomes the basis for others such as flow rate and level. It is important that any differential low pressure transmitter will remain accurate despite other changes in the atmosphere. Differential pressure can also be used to measure things such as viscosity, density and sometimes temperature. Differential pressure is used in many applications from sprinkler systems to water treatment plants and from heating systems (hot water or steam) to metering offshore gas and oil flows.
Gauge Pressure
Gauge pressure is defined as the difference between atmospheric pressure and the pressure to be measured. In other words, the pressure in the atmosphere (as it stands for any particular test) must be removed before an accurate pressure test can be achieved on any one thing.
Low pressure transmitters may measure any of these types of pressure. It is important to know which type you need measured and the atmosphere where the transmitter will be located in order to select the best transmitter for the job. Be sure to have the pressure level and accuracy requirements handy when you begin your
search for a low pressure transmitter for any situation.