Delavan Sonac© 120 Ultrasonic Switch

Delavan Sonac© 120 Ultrasonic Switch

The Sonac© 120 is a reliable level control that will sense almost any liquid. Its fail-safe features ensure positive level control in critical processes. The non-intrusive feature of its sensor permits its installation in extremely small vessels and pipes.

Non-dedicated vessels – liquids
The device senses virtually any liquid and does not need adjustment when the density or dielectric constants are changed.

High temperature, high-pressure service
The welded, all stainless steel sensor body is designed for service at temperatures to 400°F (+205°C) and pressures to 2,000 psig.

Fluids with foam blankets
The control ignores foam to sense the true liquid level. Precision level control requirements Repeatability to 0.050 inches standard.

Principle of Operation
The sensor is a magnetostrictive device consisting of a diaphragm, nickel tube, magnet, drive coil, and pickup coil. When power is supplied to the drive coil, it causes the diaphragm to vibrate at a frequency determined by the mechanical resonant system of the sensor. Electrical energy is transferred to the pickup coil when the diaphragm is free to move in gas. When the diaphragm motion is loaded by a liquid, less energy is transferred to the pickup coil.

The pickup coil of the sensor is connected to the input of an amplifier and the output of the amplifier to the drive coil to form a feedback loop circuit. Any energy appearing in the output of the probe will be fed to the amplifier, amplified, and returned to the input of the probe. This causes vibrations at 40kHz to occur in the diaphragm and furnish a signal back to the amplifier for re-amplification. When the gain of the amplifier is adjusted so as to exceed the losses within the probe, continuous oscillations are produced.

If the diaphragm of the sensor is exposed to a liquid material that offers greater mechanical resistance to the motion of the diaphragm, the transfer of energy to the pickup coil decreases. This results in a decrease in the signal feedback into the amplifier and a corresponding decrease in the signal available from the output of the amplifier. The decreased signal triggers a voltage-sensitive network that controls the output relay.

A unique AUTO TEST self-checking circuit constantly verifies the integrity of the sensor circuits. If the frequency of the sensor circuits changes beyond a certain limit, the RED LED will go out. If the change of state occurs due to a level change, the relay will follow and change its state. However, if the change of state is due to a sensor failure or some other component failure, the relay will immediately de-energize to the alarm condition. This foolproof feature protects the system from loss of power, major component failure of damaged sensor conditions.



  • Autotest self-checking
  • Really fail-safe
  • Stable, dependable performance
  • Corrosion-resistant sensors
  • No false trips due to surge or splashing liquids
  • Corrosion-resistant, watertight remote enclosure
  • Versatile power supply


Single Point Level Switch For On-Off Control Of Liquids

  • Service At Temperatures To 400°F
  • Autotest Self-Checking
  • Really Fail-Safe
  • Stable, Dependable Performance
  • Corrosion Resistant Sensors


  • Supply Voltage:
    115 Volts AC
    230 Volts AC
    24 Volts DC
    90-135 Volts AC
    180-270 Volts AC
    +/- 4 Volts AC
  • Power: 3 volt-amperes
  • Frequency, AC Power: 50-60 Hz
  • Delay time range: 50 milliseconds min. to 10 seconds min. long delay @ 30 seconds max.
  • Fail-safe:
    Switch selectable - high-level or low-level
    high-level fail-safe position: relay is de-energized when product is present (wet)
    Low-level fail-safe position: relay is de-energized when product is not present (dry)
  • Indicators: Two, light-emitting diodes (LED); YELLOW - illuminated when relay is energized; RED - illuminated when product is present at sensor
  • Operating Temperature: -40°F to +160°F (-40°C to +71°C)
  • Output: Relay, DPTDT form C
  • Ratings: 
    5 amp @ 120 Volts AC resistive
    3 amp @ 240 Volts AC resistive
    3 amp @ 24 Volts DC resistive
  • Maximum cable length: 
    PVC - 100 feet (30.5M)
    Teflon - 60 feet (18.3M)
  • Shipping weight:
    Control unit - 5 pounds (2.25 kilograms)
    Sensor - 1.5 pounds (0.68 kilograms)
    Cable - 0.5 pounds (0.45 kilograms)


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