The gas density transmitter GDS-M continuously monitors the pressure and temperature of the insulating gas SF6. For this purpose it possesses a piezoresistive pressure sensor and an evaluation unit with microprocessor. The measured values can be transmitted to a PC or the customer’s own diagnostic system.
Key Features
Design
The gas density transmitter GDS-M consists of the following principal components:
Operating principle
By way of its piezoresistive sensor, the gas density transmitter GDS-M continuously measures the gas density and temperature in the relevant gas chamber. The signals generated by the sensor 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 GDS-M is capable of actively monitoring the gas density. The gas density transmitter also facilitates the monitoring of SF6 emissions from high-voltage systems. The GDS-M can likewise be programmed to monitor the density of other gases.
Measuring method
Based on the high-precision, digitally compensated pressure and temperature signals of the piezoresistive pressure sensor, the actual gas density is calculated with an optimal approximating polynomial for SF6 gas density. The correct density value is read out with a cycle time of 64 ms.
Fields of application
| Measurement ranges |
SF6 density acc. to Beattie-Bridgeman formula | 0 … 67 kg/m³ |
| Pressure | 0.5 … 11 bar abs. / 7.25 … 159.5 psi abs. | |
| Temperature | –40 … +80 °C / –40 … +176 °F | |
| Overload pressure | 30 bar | |
| Accuracy (RS-485) | Total error band, pressure | < ± 0.5 % FS |
| Total error band, temperature | < ± 1 % FS | |
| Stability error, pressure | < 0.1 % FS | |
| Stability error, temperature | < 0.3 % FS | |
| 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″ or G 1/4″ (standard) Customer-specified flange (optional) |
|
| Electrical connection |
Connector | Round plug connector M12 x 1 / 8 contacts |
| Supply voltage | 8 … 30 VDC | |
| Power requirement | < 3 mA | |
| Reverse polarity protection | Yes | |
| Short circuit protection | Yes | |
| Protection class | IP 65 IAW IEC 60947 | |
| Interfaces | Digital interface (incl. integrated comm. interface) |
RS-485 |
| Readout cycle | Every 64 ms | |
| Response time (typ.) | 1 … 10 ms (2 … 5 ms) | |
| Housing material | Stainless steel 1.4305 | |
| Weight | 185 g |
