Contact ultrasonic level switch technology was first applied to process control in the 1960s – and continues to provide accurate and reliable liquid level measurement in virtually every process industry today.
How an Ultrasonic Level Sensor Works
An ultrasonic level switch utilizes 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 ultrasonic level sensors 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.
Expect Advanced Performance and Enhanced Safety From an Ultrasonic Level Sensor
Ultrasonic contact technology provides liquid level measurement in virtually every process industry, including chemical, petrochemical, power, water and wastewater, pulp and paper, food, and pharmaceutical industries. Ultrasonic level switch devices are typically used in a wide array of industrial applications that can help prevent equipment damage, including pump control, pump protection and seal pot level control. Additionally, ultrasonic contact technology offers important tank overfill protection safety features, including high level alarms, that can help your process plant, pipeline terminal or tank farm comply with API RP 2350 4th edition updates.
Specific design features of ultrasonic level switches are intended to enhance safety in process environments. In the information below, Echotel® contact ultrasonic level switches from Magnetrol® are used to highlight available safety features.
- Low cost single- and dual-point sensing is accurate and reliable in a wide variety of liquids.
- Dual-point option is ideal for two-alarm safety protocol configuration.
- Advanced self-test technology provides unsurpassed testing of electronics, transducer, piezoelectric crystals and electromagnetic noise, which makes this technology suitable for use in Safety Integrity Level (SIL) 2 loops.
- Best-in-class safe failure fraction of greater than 91%.
- Adjustable time delay for turbulent aerated liquids that prevents false level alarms due to waves or splashing.
- Integral or remote mount electronics enable easy installation and simple configuration.
- Remote mount capability keeps workers off top of tank for switch modification.
- Pulsed signal technology works well in challenging process conditions such as aeration, suspended solids and high viscosities.
- Extensive FM, CSA and ATEX explosion proof and intrinsically safe approvals.
- The ability to transmit a stable signal despite liquid property changes in specific gravity, conductivity, pH and dielectric or temperature shifts.
- Electronic switches contain no moving parts, which prevents degradation and high maintenance costs.
Additionally, ultrasonic level switches compare very favorably to tuning fork technology, which can have a negative impact on performance and profitability due to the time and labor required to calibrate tuning fork level switches. For more information about how ultrasonic level switches compare to tuning forks, view the MAGNETROL video on the subject.