
Pressure Sensors, Transmitters & Gauges

Pressure gauges are used to measure and display the pressure of a liquid or gas in a system. Pressure systems are designed to operate within a specific pressure range and pressure gauges can indicate if there are pressure changes or leaks that could affect the system performance. Analog pressure gauges utilize mechanical pressure sensing technology and display the measurement using a needle movement on a dial. The needle gives a visual indication of the pressure. They do not require a power supply to operate, but are susceptible to operator error in reading the dial. Digital pressure gauges use an electro-mechanical form of measurement along with circuitry to translate the value to a reading on a display screen. They are more accurate and reliable over a wider temperature range and have remote monitoring capabilities.
Pressure sensors detect, regulate or monitor pressure and convert the input data into an electronic output signal. Gauge pressure sensors measure pressure relative to atmospheric pressure. Absolute pressure sensors measure pressure relative to absolute zero pressure. This allows for very precise measurements. Differential pressure sensors use two different pressure ports and measure the difference between the two.
Pressure transducers convert an applied pressure into a measurable electrical signal that is proportional to the applied pressure. An elastic material inside of a pressure transducer will deform when exposed to a pressurized medium and an electrical device will detect the deformation and convert the result into a usable electrical signal. The electrical signal is not linearized or temperature compensated.
Pressure transmitters amplify, linearize and compensate the signal from a pressure transducer and transmit the signal to a remote receiver.
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2 pieces of hardware used in modern day instrumentation: measuring elements and transmitters.
Measuring elements are the part of the device that performs the measurement. For example, the measuring element of a pressure transducer is the part that is actually lowered into a tank that will take a pressure measurement. The measuring element of a flow meter is the part that actually measures the flow and an RTD or thermocouple takes the temperature measurement.
Transmitters collect information from measuring elements and sends the information to where it is needed. The transmitter interfaces with the measuring element and interprets the information. It then sends that information to a PLC, RTU or some other type of control unit. In many cases, the transmitter has the ability to communicate the information via multiple communication protocols. This may be necessary when the measuring element does not send the same type of signal that is needed by the controller. For example, it may be necessary to convert a temperature reading from a thermocouple to a 420 milliamp signal that can be received by a local PLC.