Level Switches & Transmitters
Level control and measurement in industrial processes is essential to optimize performance and avoid potential problems. Level measurement determines the position of a liquid relative to the top or bottom of a container. Levels that are too high can cause overflow, resulting in safety or environmental problems, while levels that are too low can cause damage to equipment. Fluid level control devices monitor, compare and regulate liquid levels within a process to a set value.
Mechanical float switches float on top of a liquid and move vertically as the level rises or falls. When the level is above or below a specific set point, the mechanical switch opens or closes, allowing an electrical current to pass through a connected device. The connected device can control valves to open or close, control pumps to let water in or out or trigger alarms to signal a problem.
Capacitive level transmitters are based on the principle of capacitance sensing. When the height of the measuring electrode changes by the liquid, the capacitance changes. Capacitance changes can result from the height of the liquid in a tank changing between the electrode and the tank wall.
Submersible level transmitters are submerged directly into the liquid to be measured and are positioned as close to the bottom as possible. The submersible pressure sensor measures the hydrostatic pressure, which correlates to the to the height of the liquid above.
Ultrasonic level transmitters are designed to measure liquid level by emitting pulses of sound at the liquid surface and calculating the time it takes for the sound wave to bounce back to the sensor. The farther the sound travels, the lower the liquid level.
Pump controllers monitor and display present liquid levels and can be programmed to control one or more pumps to turn on or off, depending on preset liquid level values.
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Transmitters vs Transducers
Some of the most common types of transmitters and transducers can be found on pressure instruments. Examples of these include: drop-in well pressure devices and devices that measure the pressure in a pipe or gas chamber. Transmitters and transducers can also be found on flow and speed measurement devices.
What is the difference between transmitters and transducers?
The main difference is the way they send data to the monitoring device, like a PLC. In terms of measurement, the transmitter will reference a measuring unit by sending a milliamp signal (such as 4-20 mA). A transducer will reference a measuring unit by sending a voltage signal, typically in volts or millivolts.
Why have the two different types of transmission methods?
The method will depend on the application. If the electrical connection in the application travels a short distance, a pressure transducer is the better choice. Pressure transducers are smaller with fewer active electronic components that can be upset by electromagnetic interference. Also, the voltage signals transmitted over longer distances are subject to voltage drop and signal corruption. A transmitter is better for transmitting signals over a long distance.