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Gas Density and Dew Point Transmitter GD-DP

Transmitter for monitoring the gas density and dew point in SF6 gas-insulated high-voltage systems

The GD-DP continuously monitors both the density and temperature of the insulating gas SF6 and the dew point. For this purpose it possesses a piezoresistive pressure sensor, a polymer dew point sensor, and an evaluation unit with microprocessor. The measured values can be transmitted to a PC or a customer-specific diagnostic system.

The product development was financially supported by the Ministry for Economic Affairs and Energy of the state of Brandenburg.




Key Features

  • Pressure range 0.5 to 10 bar absolute
  • Dew point range -30 to +40 °C
  • Microprocessor evaluation unit
  • Digital compensation for pressure and temperature signals
  • Digital output
  • Interface RS-485 Modbus RTU
  • Degree of protection IEC 60529: IP 65



The gas density and dew point transmitter GD-DP consists of the following principal components:

  • Tubular casing, stainless steel grade 1.4305
  • Piezoresistive pressure sensor
  • Capacitive polymer dew point sensor
  • Electronic evaluation unit with microprocessor
  • Pressure connection G 1/2″
  • Electrical connection with circular connector M12x1

Operating principle

By way of its piezoresistive sensor, the GD-DP continuously measures the gas density and temperature in the relevant gas chamber. At the same time, the device’s capacitive polymer dew point sensor continuously monitors the current dew point. The signals generated by the sensors are digitally compensated by the evaluation unit with microprocessor and presented as a high-precision output signal. The output signal is transmitted to a connected PC or the customer’s own diagnostic system. The measured values can then be used for documentation, trend analysis or other purposes.

Unlike electromechanical density monitors, which serve only as simple switches when the loss of SF6 violates set limit values, the GD-DP is capable of actively monitoring the gas density and dew point temperature. The transmitter also facilitates the monitoring of SF6 emissions from high-voltage systems. The GD-DP can likewise be programmed to monitor the density and dew point of other gases.

The information on this website represents the state of knowledge at the time of writing. Technical specifications are subject to modifications. Comde-Derenda GmbH accepts no liability whatsoever for the content provided or for damages resulting from the use of its products.

Technical Data

Measurement ranges
SF6 density acc. to Beattie-Bridgeman formula 0 … 67 kg/m³
Pressure 0.5 … 10 bar abs. / 7.25 … 145 psi abs.
Dew point temperature –30 … +40 °C / –22 … +104 °F
Relative humidity 0 … 100 % RH
Overload pressure 16 bar / 232 psi
Total error band, pressure < ± 0.5 % FS
Total error band, temperature < ± 1 % FS
Total error, dew point temperature < ± 2 K *
Total error, absolute humidity < ± 0.2 g/m³ *
Stability error, pressure < 0.1 % FS
Stability error, temperature < 0.3 % FS
Stability error, dew point temperature < 1.5 K *
Stability error, absolute humidity < 0.15 g/m³ *
Measurement response time < 10 sec
Operating and storage conditions
Operating temperature –40 … +80 °C / –40 … 176 °F
Storage temperature –50 … +85 °C / –58 … 185 °F
Shock resistance (IEC 60068-2-29) 100 x 20 g / 6 ms half-sine
Switch impulse test 20 g / 5 x 20 ms sine
Pressure connection
G 1/2″ (standard)
Electrical connection
Connector Round plug connector M12 x 1 / 8 contacts
Supply voltage 8 … 30 VDC
Power requirement 2.6 … 2.7 mA
Short circuit protection Yes
Protection class IP 65 IAW IEC 60947
Interface Digital interface RS-485 Modbus RTU
Response time (typ.) 1 … 10 ms (2 … 5 ms)
Housing material Stainless steel 1.4305
Weight approx. 170 g
* Calibration once a year is recommended. Total error of dew point temperature is only guaranteed for ambient temperature ≥ 20 °C.
For real dew point temperatures of ≤ -20 °C, the total error can be significantly higher (see datasheet for further information).

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