■ GDT.857, SF₆ Gas Density Monitor (Analog Output)

- SF₆ gas density monitoring with analog current output

- Selectable 4…20 mA / 6.5…20 mA analog current output

- MEMS pressure sensor (accuracy ±0.5% F.S)

- Up to 4 selectable micro-switches (SPDT contacts)

- Dedicated SF₆ temperature compensation software; measuring range up to 0…11 bar abs.

- Various axial / radial process connections and high shock resistance

 

■ Product Overview

The GDT.857 is an SF₆ gas density monitor with analog current output. It combines a dial indicator and micro-switch functions with a MEMS pressure sensor-based analog current output for monitoring SF₆ gas conditions in high-voltage electrical equipment.

A sealed bellows chamber filled with reference SF₆ gas and a pressure sensor monitor changes in gas density caused by temperature fluctuations. Dedicated temperature compensation software supports accurate switching outputs and long-term stability.

The MEMS pressure sensor provides a selectable 4…20 mA or 6.5…20 mA analog current output, with sensor accuracy of ±0.5% F.S according to IEC 61298-2. The analog output configuration depends on the selected option.

Up to four SPDT micro-switches are available. Various axial / radial process connections and installation orientations allow flexible integration into equipment.

Typical applications include SF₆ gas density monitoring, high-voltage circuit breakers, SF₆-insulated busbar systems, and gas-insulated substations (GIS).

■ Applications

▶ SF₆ gas density and condition monitoring systems

▶ High-voltage circuit breakers

▶ SF₆-insulated busbar systems

▶ Gas-insulated substations (GIS)

■ Key Performance and Configuration Options

▶ Analog current output: selectable 4…20 mA / 6.5…20 mA

▶ Analog output range: 4…20 mA = 0…60 kg/m³; 6.5…20 mA = 0…56.1 kg/m³ (both 0…1250 kPa abs. @ 20°C)

▶ MEMS sensor accuracy: ±0.5% F.S (according to IEC 61298-2)

▶ Sensor power supply: 12…30 VDC / micro-switches: 1–4 (SPDT)

▶ Switching set-point accuracy: ≤ ±10 kPa @ 20°C / temperature accuracy: ≤ ±1°C

▶ Dial units: bar / MPa / kPa / psi / kgf/cm² / scale markings: Green / Yellow / Red

▶ Cable gland: M20×1.5 / connection orientation: axial or radial (radial: bottom / left / top / right)

■ General Specifications

Measuring Range	Up to 0…11 bar abs.
Monitoring Principle	Absolute-pressure measurement using a sealed bellows chamber filled with reference SF₆ gas and a pressure sensor
Sensor Principle	MEMS Pressure Sensor
Analog Current Output	4…20 mA / 6.5…20 mA (selectable)
Analog Output Range	4…20mA:0…60kg/m³ 6.5…20mA:0…56.1kg/m³ Both: 0…1250 kPa abs. @ 20°C
MEMS Sensor Accuracy	±0.5% F.S (according to IEC 61298-2)
Sensor Power Supply	12…30 VDC
Switch Contacts	1–4 Micro-switches / SPDT (Change-over)
Switch Rating	AC 250 V / 6(2) A (Resistive Load)
Switching Accuracy	≤ ±10 kPa @ 20°C
Temperature Accuracy	≤ ±1°C
Temperature Compensation	-20…+60°C
Operating Temperature	-40…+80°C (Operating / Ambient / Storage)
Electrical Connection	Cable Gland M20×1.5 / IP67
Process Connection	G1/2 Male / M20×1.5 Male / Swivel Nut / Fitting / Flange, etc.
Installation Direction	Axial / Radial (Bottom / Left / Top / Right)
Material	Wetted Parts / Body / Connection / Bellows: Stainless Steel 316L Housing: Aluminium
Leakage Rate	≤ 5×10⁻¹⁰ mbar·L/s (Helium Leakage Inspection)