Digital communication in sample conditioning systems
May 10 2022
When extracting sample gas from the process, process-related impurities such as particles or moisture are inevitably also extracted. These can affect the measurement results or damage the measuring cells. The sample gas must therefore be prepared before it enters the analyser. To remove moisture, the gas temperature in the sample gas cooler is lowered below the dew point. The resulting condensate is discharged.
The cooler is controlled by a microprocessor. Falling below or exceeding the set warning range (e.g. after switching on) is signaled both by the flashing of the LEDs and by the status relay. The status output can e.g. B. can be used to control the sample gas pump to enable the gas flow to be switched on only when the permissible cooling range is reached. By connecting a humidity sensor, the controller can be expanded to monitor condensate breakthroughs.
So far, the measured cooling block temperature could be transmitted via an analogue 4 - 20 mA signal. As digitisation continues to advance rapidly, Bühler Technologies GmbH will in future make the more advanced Modbus RTU communication protocol available as an option for all sample gas coolers with semiconductor cooling elements. This digital interface represents a higher authority, such as e.g. B. the control system has extended information about the sample gas cooler.
With the option of the Modbus RTU digital interface, the user now has direct access to the process and diagnostic data, for example the current cooling block temperature or information about a possible temperature error if this is outside the target range. If a humidity sensor is connected, e.g. B. also a moisture breakthrough can be determined directly from the control station. All settings that could previously be made via the menu on the display of the sample gas cooler can now be made remotely from the control room and directly during operation. The condensate pumps can be activated and deactivated again as required, the setpoint of the cooling block temperature can be adjusted and the alarm thresholds can also be set remotely. New functions are also the output of the cooler's utilisation (in %), which is helpful for evaluating the performance limit, and the output of the device runtime, which can be used to implement maintenance intervals.
Modbus RTU is considered a very robust interface and enables remote access to the sample gas cooler from Bühler Technologies GmbH to control and monitor the current status, robust and reliable communication between field devices and the control system and thus supports safe and continuous process and plant operation.
The following sample gas coolers are available with Modbus RTU:
- Electric Gas Coolers
- Gas Cooler RC 1.1
- Gas Coolers 1.2+
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