Hotwire Liquid Water Content Sensor (LWC-300)


A compact instrument that precisely measures liquid water content (LWC) from 0 to 3 g/m3.
Optional Feature: Aspirator for Ground Use




The LWC-300 can be easily mounted on manned or unmanned aircraft, cooling towers, and spray rigs.
The LWC-300 offers several advantages over earlier versions of the LWC:
  • Improved electronics that extend sensor lifetime
  • Reduced background noise
  • Improved frequency response
  • RS-422 serial communication
The LWC-300 features an interchangeable circuit card sensor for quick replacement.


Optional Feature

DMT has developed an aspirator for ground-based LWC applications. The system, pictured below, is a self-contained unit that includes the fan. An external flow indicator provides easy access to airflow readings.


The Particle Analysis and Display System (PADS, shown at right) is optional software that provides a user-friendly virtual instrument panel. PADS allows the user to control the LWC and display and log data. For instance, the program enables the user to do the following tasks:

  • Start data recording and sampling
  • Automatically estimate LWC from convective heat losses, wire temperature, air density, and various constants and intermediate values
  • Estimate convective heat losses using direct measurements or an empirically derived method


How It Works

The hot-wire liquid water sensor features a coiled wire that is maintained at 150° C. This coil acts as a variable resistance in one arm of a Wheatstone Bridge circuit. The resistance of the sensing coil decreases as the wire temperature decreases. Temperature decreases can be caused by vaporization of water droplets or by convective heat losses to air that flows past the sensor. Heat losses by conduction from the ends of the master coil are minimized by slave coils that are maintained at the same temperature as the master coil and are located at each end of the master.

The resistance of the sensing coil is directly proportional to its temperature; therefore, the control circuit maintains the sensor at constant temperature by maintaining it at constant resistance. A Wheatstone bridge is formed of four resistances, of which the master coil sensor is one. The power dissipated by the sensor is the product of the current through the sensor and the voltage drop across it.

Once the power dissipated by the sensor is known, the effects of convective heat losses are estimated. The power dissipation due solely to vaporization can then be estimated, which in turn gives an estimate of liquid water content.



Parameter Specification
Measured Parameters Liquid water content in the 0-3 g/m3 range
Air Speed Range 0 - 200 m/sec
Calibration Not Required
Frequency Response >25 Hz
Output RS-422 Serial Communication
Special Features
  • Interchangeable circuit card sensor
  • Pulse width modulation control (avoids overheating of the power transistor and hotwire coil)
Mounting 2.5-inch diameter B.C. Rosemount pattern mounting
Power Requirements System power: 28 VDC, 7.5 A max
Anti-ice power: 28 VDC, 8.0 A
Weight Electronics box: 500 g
Sensor strut: 600 g
Dimensions Sensor strut with strut mount: 11.5 cm W x 6.4 cm L x 19.5 cm H (41/2” W x 2 1/2” L x 7 5/8“ H)
Electronics box: 12.1 cm W x 12.1 cm L x 6.7 cm H (43/4” W x 43/4” L x 25/8” H)
Electronics box mounting plate: 9.7 cm W x 15.3 cm L x 0.3 cm H (3.8” W x 6.0“ L x 0.1” H)
Operating Limits 0 -12 km altitude
-40 to +40 °C
0 - 100% RH


Included Items

  • Instrument (sensor strut and electronics box)
  • Interconnect cable
  • Operator Manual
  • One-year warranty

Accessories (Purchased separately)

  • PADS software and laptop
  • Aspirator


How to Order

Contact DMT for pricing or more information.


Phone: +001 303 440 5576
Fax: +001 303 440 1965