Pressure Transmitter
Pressure transmitters translate low-level electrical outputs from pressure sensing devices to higher-level signals that are suitable for transmission and processing. In general, a transmitter is a signal converter for translating the signal into something that can be sent over a distance. Many pressure transmitters have an integral sensor such that they can measure a pressure signal as well as transmit this signal some distance. Transmission may be via an analog signal such as 4-20ma or a digital signal such as Ethernet.
Pressure Transmitter Technology
Pressure transmitters use many different sensing technologies and can measure the pressure of liquids and/or gases. These include mechanical deflection devices such as:
-Diaphragms
-Bourdon tubes
-Sealed pistons or cylinders
-Strain gauges
-Piezoresistive devices
-Piezoelectric pressure transmitters
-Thin film devices
-Microelectromechanical systems (MEMS)
-Variable capacitance
-Vibrating elements
Pressure Measurements
Pressure transmitters are capable of performing various pressure measurements and displaying amounts in different units.
-Absolute pressureis a pressure measurement that is relative to a perfect vacuum. Typically, vacuum pressures are lower than the atmospheric pressure.
-Gage pressure, the most common type of pressure measurement, is relative to the local atmospheric pressure. By contrast, sealed gauge pressure is relative to one atmosphere of pressure at sea level.
-Differential pressurereflects the difference between two input pressures.
-Compound pressureinstruments can display both positive and negative pressures.
Performance specifications for pressure transmitters include:
-Working pressure range- Working pressure is the maximum, allowable pressure at which pressure transmitters are designed to operate. Typically, devices should not exceed 75% of their maximum, rated range.
-Vacuum range- Vacuum range, another important measurement, covers the lowest vacuum pressure and the highest vacuum pressure.
-Accuracy- Accuracy, the difference between the true value and the indication, is expressed as a percentage of span. In cases where the accuracy differs between the middle span and the first and last quarters of the scale, the largest percentage error is reported.
-Operating temperature- Operating temperature is the full-required range of ambient operating temperatures. Temperature and pressure are directly related to each other. If the temperature of the operating environment increases the pressure in the system will increase. In order to prevent equipment damage, it is important to know the extreme temperature ranges of the area.