Gas mixer switch-over

Double redundancy through gas mixer switching with double gas analysis and backup system

878 494 Alexander Hanf

A German automobile manufacturer demands special security when it comes to the supply with welding gas. A redundant supply conceptwith two LT gas mixers and a back-up bundle supply is used for this. Every week, there is an automatic switch-over between the two gas mixers in order to ensure that they are used evenly and that both gas mixers function properly.

If the regular gas supply is disrupted, the system switches to an emergency supply (bottle station) with ready-to-use mixture installed in the mixing room.

In addition, it is possible to operate both gas mixers in parallel via additional pressure signals if the gas mixture is required at times.

In addition, a redundant analysis systemwith double analysis, i.e. with two independent measuring cells, is installed. Two NDIR sensors measure continuously the CO2 concentration in the Ar/CO2 gas mixture. Each measuring cell is responsible for one gas mixer, which guarantees independent redundancy. The analysis results are shown on the color display integrated in the local control system. The gas analysis is supervised via magnetic valves with the sample gas of the corresponding gas mixer and also has an automatic zero and end point calibration.

Switchover and gas analysis are controlled via a common PLC with a touchscreen display. The operating status of mixer one or two is displayed next to the measured value. For a quick overview, two indicator lights also show the currently activated gas mixer.

Messages such as

  • Operating status gas mixer 1/2
  • Interuption mixer 1/2
  • Limit values
  • Analysis of actual value mixer 1 and 2 of the continuous measurement as an analog signal

are transferred to the central control room via a cable connection.

The analysis values are logged in the control and can be read out as a CSV file via a USB slot on the front of the housing and can be processed with common software tools.

This ensures the special security required for the welding gas supply and the continuous gas mixture analysis to meet the highest quality requirements.

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