System pressure measurement is one of the most important variables to measure and control in a pumping system. It provides information about system pressure and the pump or system operation, and it can be used to control the system in an efficient and reliable manner.
The simplest form of pressure measurement is with a pressure gauge. A pressure gauge is a pressure indicating device that provides a local readout of pressure to monitor the operation or condition of a process by locally indicating a quantity of pressure. There are many types of pressure gauges, but the most common is the analog indicating bourdon tube type.
A pressure switch is next on the list.
It may have a digital display, but the display is not the primary objective of a switch.
A pressure switch is a device that, after the deviation of a physical pressure, opens or closes a set of contacts. The pressure setting can typically be adjusted and is used to open or close a valve or turn a pump on or off based on the physical pressure.
A pressure transducer or transmitter is an electronic device used in combination with a pressure sensor and voltage-to-current signal conditioner to generate a proportional output to the pressure it is reading, such as 4–20 mA or 1-5 volt (or other type) output signal. This proportional pressure signal can be fed to a distributed control system or other control to continuously manage the operation of a pumping system.
A typical application for control with a pressure transmitter and controls system is the modulation of a control valve or modulation of pump speed through a variable speed drive to maintain system pressure set point.
Pressure gauges, switches and transducers can read, indicate and/or control based on positive, negative (vacuum) or differential pressures.
Table 1. Relative capabilities of pressure sensing devices
Tables 1 and 2 provide a summary of the capabilities and relative cost of each type of device and considerations for selection and measurement.
Table 2. Important selection and measurement considerations
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