Level Sensing with Ultrasonic Contact Technology

Reliable level instrumentation is required to improve process efficiency and ensure the safety of your facility and your employees. Whether you’re specifying liquid level controls for a paper mill or a facility that processes natural gas, chemicals, petrochemicals, power or water and wastewater, finding high-quality instrumentation that can accurately measure level in your clean liquid applications is a mission-critical requirement.

During the next three weeks, we’ll discuss ultrasonic contact technology to provide an overview of how the technology works, application considerations and a comparison to other level control technology, specifically tuning forks. Consider subscribing to this blog to receive the complete discussion.

Contact ultrasonic devices provide liquid level measurement in virtually every process industry. Ultrasound technology was developed during World War II under the acronym SONAR (SOund Navigation And Ranging). Ultrasonic level measurement was first applied to process control in the 1960s – and continues to play a significant role in liquid level measurement today.

Continuous-Wave and Pulsed-Signal Sensing
Ultrasonic contact level sensing is achieved by either continuous-wave or pulsed-signal technology. Continuous-wave switches use two piezoelectric crystals positioned opposite each other across the transducer gap.

The transmit crystal generates an acoustical signal that the receive crystal converts into an electrical signal. When liquid is present in the transducer gap, the amplifier becomes an oscillator causing a relay circuit in the electronics to indicate a wet gap condition. When liquid vacates the gap, the amplifier returns to an idle state.

Pulsed-signal models feature a digital electronic amplifier that produces a powerful pulse of ultrasonic energy five to ten times stronger than most continuous wave units do. This pulsed-signal technology provides more accurate measurement in conditions of aeration, suspended solids, turbulence and highly viscous liquids.

The transmit crystal of pulse signal units generates pulses of high-frequency ultrasonic energy only milliseconds in duration. In between each pulse, the receive crystal “listens” for the transmission. If liquid is present in the gap, the receive crystal detects the pulse and reports a wet gap condition to the electronics. When the gap is filled with air, the receive crystal cannot detect the pulse, and reports a dry gap condition.

Ultrasonic Contact Technology

Up Next
In our next post, we’ll review various application considerations that affect the specification of ultrasonic level control technology. For more information on this subject, you can also download the MAGNETROL Contact Ultrasound Technology Guide.



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