Dew Point Moisture Analyzer DP-250


Dew Point Moisture Analyzer DP-250

HNL’s microprocessor-based Direct moisture measurement instruments are accurate, reliable and fast. They provide a direct measurement of the moisture content and temperature of the oils for better maintenance of transformer and equipment.

  • Provides measurement of the relative saturation of water and temperature of the oil.
  • Effectively monitors oil reconditioning, such as when to change filters, or to stop the process.
  • Continuous measurement allows for estimation of the moisture content of the transformer insulation system and hazardous conditions, which may occur during temperature cycling, helping prevent transformer failures.
  • The sensor operates directly in the oil so it can be installed directly into the transformer or processing equipment
  • Saturation or air parts per million (ppm) Extremely versatile
  • Inbuilt Thin film water vapor sensor
  • Optional RS 232 Computer Interface & Data Logger

The determination of moisture in the oil is an essential part of a comprehensive transformer maintenance program. Excessive moisture contents cause accelerated aging of the insulation materials and reduce their dielectric strength. In extreme cases, this can result in arcing and short circuits within the windings. Accurate moisture measurements can also warn about leaks in the oil system, as water is absorbed from the surrounding air.

The water solubility of transformer oils versus temperature. The marginal shows the range of variation of water solubility found in actual mineral oils.

Moisture levels in oil are affected by temperature cycling of a transformer. The water solubility of the oil is temperature dependent water solubility increases as temperature rises.


Relative Saturation (RS) 0 to 100 %
Concentration, Parts Per Million Of Water (ppm) mg/kg
Accuracy, including non linearity upto 0-90 % RS ± 1 %
Repeatability 90-100 % RS ± 2 %
Temperature Measurement Range -20 to 100 °C
Sensor Types Water Sensor : Thin Film Polymer
Temperature : Pt 100 RTD 1/3
Pressure Range of Sensor Head (Probe) 20 kg/cm2
Two Analog Outputs (default) 4-20 mA
Modbus Protocol MOD RTU (RS 485)
Baud Rate 9600
Relative Saturation in Oil 0 to 100 % RS
Temperature Measurement Range -20 to 100 °C
Local Display / Keypad 2 x 16 Character LCD Alphanumeric
Keyboard 1 x 4 Keypad
Operating Temperature Range 0 to 50 °C
Power 24 V DC, or 230 V AC
Sensor Protection Sintered S/S Filter
Probe Dimensions 24 V DC, or 230 V AC
Operating Temperature Range for Electronics -40 to +60 °C
Cable Length 2 M


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