Delavan Sonac® 1000 2-Wire Switch

Principle of Operation
The sensor is a magnetostrictive device consisting of a diaphragm, nickel tube, magnet, drive coil, and pickup coil.

When 40kHz energy is applied 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 process 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 sensor will be fed to the amplifier, amplified, and returned to the input of the sensor. This causes oscillations at 40kHz to occur in the diaphragm. When the gain of the amplifier is adjusted so as to exceed the losses within the sensor, continuous oscillations are produced.

If the diaphragm of the sensor is exposed to a process liquid that offers 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 4-20mA step-change output current.

A change of state condition (sensor covered by liquid) will cause a step change in current in the output circuit. This can be used to operate a remote relay or develop a voltage that will indicate a change in level to a computer or data logging system. Multiple sensors can be operated from a single power supply.

The Delavan Sonac® 1000 may be powered by the user's 12 or 24-volt power supply or a Delavan 920-2F power supply with two control relays. The 920-2F provides a relay output with 1 Form C SPDT contacts, the power supply operates with a supply voltage of 115 or 230 Volts AC, 50-60Hz.

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  • Two-wire transmission
  • Isolated output
  • Fault indicator
  • Non-dedicated vessels - liquids
  • Intrinsic safety
  • Stable, dependable performance
  • No false trips due to surge or splashing liquids
  • Hermetically sealed
  • Fail-safe
  • Non-intrusive
  • Rugged
  • No field calibration


True "Two-Wire" Single Point Switch for on-off control of liquids

  • 4mA,20mA Output
  • Intrinsic safety
  • Hermetically sealed
  • Fail-safe
  • Non-intrusive



  • Supply voltage :
    12 Volts DC at 20 mA, 20 ohms
    24 Volts DC at 20 mA, 600 ohms
  • Power: Less than 1 volt-amperes
  • Time delay: 1 second fixed
  • Fail-safe (4mA nominal):
    High-level fail-safe: power lost indicates wetted sensor (Sonac 1001)
    Low-level fail-safe: power loss indicates dry sensor
  • Operating temperature: -60°F to +160°F (-50°C to +75°C)
  • Output: 4 or 20 mA +/- 2 (nominal) step change
  • Sensor housing: Meets NEMA 4, 5, 12
  • 347 Stainless steel: NEC Class I, Groups C, D; Class E, F, & G when installed in compliance with appropriate electrical code

Delavan MW/920-2F Remote Power Supply

with 2 independent relays (serves 2 sensors)

  • Supply voltage:
    115 Volts AC
    230 Volts AC
    90-135 Volts AC
    180-270 Volts AC
  • Frequency: 50-60 Hz and 40 Hz minimum
  • Operating temperature: -40°F +160°F (-40°C to +75°C)
  • Output voltage:
    24 Volts DC at 40 mA (supplies two sensors)
    2 Relays SPDT contacts
    5 amp @ 120 Volts AC Non-inductive
    3 amp @ 240 Volts AC Non-inductive
    5 amp @ 24 Volts DC Non-inductive
  • Indicators (one set per sensor): RED LED - illuminated when sensor is wetted; YELLOW LED - illuminated when relay is energized; GREEN LED - illuminated, indicates no-fault
  • Housing  glass-reinforced polyester enclosure, stainless steel trim: Meets NEMA 4X

Note: OEM or Rack mounted power supplies are available. Consult factory.

Download Datasheet: Delavan Sonac® 1000 2-Wire Switch