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Densistat D56 / D56i0

Density monitor for SF6 gas-insulated high-voltage circuit breakers

The Densistat D56 / D56i0 is suitable for indoor and outdoor use. It incorporates an analog gauge for relative pressure, referenced to 20 °C. The type D56i0 also features a zero pressure indicator. Microswitches inside the device respond reliably to any decreases in the density and pressure of the SF6 insulating gas. The pressure connection is either straight or angled (several options are available).


Key Features

  • Pressure range 0 to 10 bar relative
  • Various pressure connectors available
  • High switching accuracy and long-time stability
  • Rugged design (IP 67/IP X5)
  • Up to 4 microswitches
  • Analog pressure gauge, can be calibrated
  • Additional zero pressure dial (D56i0)



The D56i0 consists of the following principal components:

  • Strong aluminum die-cast housing with cable gland
  • Analog pressure gauge with colored scale (55 mm diameter)
  • Additional zero pressure dial (only D56i0)
  • Electronic PCB with up to four microswitches and terminal block, switching function configurable as NO or NC
  • Aluminum pressure connector
  • Reference gas bellow, filled with SF6 gas

The cover with cable gland and the connecting cable with connectors form a single unit that is easy to dismantle with a screwdriver. The device can be supplied with a concentric pressure connection or various angled connections.

Operating principle

The Densistat D56 / D56i0 monitors gas density by way of a reference chamber filled with SF6 gas. The gas and reference chambers are separated by a metal bellows. A pressure difference corresponds to a density difference between the two chambers and deflects the metal bellows. The movement of the bellows is transmitted by a switch rod. A switching plate activates the micro­switches whose purpose is to indicate a pressure drop.

The operating points for triggering the signal can be set at the factory according to the customer’s requirements by way of lockable screws (plungers). Up to four microswitches with changeover contacts can be installed in the housing. The microswitches are installed on a circuit board together with a multipole terminal block within the housing.The connecting cable is connected to the terminal block and exits the device through a cable gland.

The analog pressure gauge shows the relative pressure of the SF6 gas, referenced to 20 °C in the gas chamber. A change in gas density attributable to a leak is indicated by deflection of the needle. The colors and transitions on the dial can be specified by the customer and calibrated to the relevant values.

The arrangement of the measuring mechanism and the use of vibration-resistant microswitches rule out any shock-induced chattering at the switching contacts. In order to prevent condensation, the unit is equipped with a Gore-Tex® equalizing membrane.


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

Indicator Analog indicator Ø 55 mm
Connector Phoenix Combicon or PTR terminal clamp
Cable gland M25 x 1.5 EMC
Microswitches 3 or 4 included, max. 2.5 mm² IAW IEC 60947
Protection IP 67 / IP X5 IAW IEC 60529
Vibration stability > 4 g (20 … 80 Hz), 0.05 bar from switching point
Pressure range 0 … 10 bar rel. / 0 … 145 psi rel.
Hysteresis < 0.1 bar / 1.5 psi (typ.)
Indicator tolerance at 20 °C ± 0.1 bar / 1.5 psi
Switching accuracy ± 0.08 bar / 1.2 psi
Response threshold ± 0.05 bar / 0.7 psi
Reference chamber leakage rate < 0.005 bar/year (5 * 10-9 mbar * l * s-1)
Electric strength 2 kV (50/60 Hz) to ground
Rated surge voltage 5 kV (1.2/50 μs) to ground IAW IEC 61000-4-5
Electric switch rating,
Resistive load (inductive load)
AC 250 V, 10 (2) A
DC 250 V, 0.2 (0.2) A
DC 220 V, 0.25 (0.2) A
DC 125 V, 0.4 (0.25) A
DC 110 V, 0.5 (0.3) A
DC 60 V, 1.5 (0.4) A
DC 48 V, 1.9 (0.7) A
DC 24 V, 3.0 (2) A
Operating temperature –40 … +70 °C / –40 … +158 °F
–60 … +70 °C / –76 … +158 °F (optional)
Storage temperature –60 … +80 °C / –76 … +176 °F
Weight 590 g
Material pressure connection AISi1MgMn, anodized
Material housing and connection box AISi12, powder coated RAL 9006
Material reference gas bellows system Stainless steel 1.4541 (bellows) / 1.4301 (bellows housing)
Material indicator window Plexiglas molding compound 8N
Material type plate, resistant to UV, ozone, climate, chemicals, and solvents 3M Scotchcal foil 3690

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