• Modbus RTU enhances communication in sample conditioning systems

Air Monitoring

Modbus RTU enhances communication in sample conditioning systems

Jun 27 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.

Bühler Technologies’ TC range of coolers, which are controlled by a microprocessor, reduce gas temperatures. Falling short or exceeding the set warning range (for example: after switching on) is indicated by both LEDs’ flashing and via the status relay. The status output 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.

Until now, 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 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 step forward in communication capabilities and the control system provides extended information about the sample gas cooler.

With Modbus RTU digital interface, the operator 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 its targeted range. If a humidity sensor is connected, it is possible to determine a moisture breakthrough 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 as necessary, the setpoint of the cooling block temperature can be adjusted and the alarm thresholds can also be set remotely. These coolers also enable the operator to determine the output of the cooler's usage (in %), which is useful for evaluating the unit’s performance limit, and the output of the device runtime, which can be used to implement maintenance intervals.

Modbus RTU is an extremely robust interface which enables remote access to Bühlers’ sample gas coolers to control and monitor its status. Robust and dependable communication between field devices and the control system therefore supports secure and continuous process and plant operation.

The TC Double, Double +, MIDI (pictured), MIDI +, MINI, Standard and Standard + models as well as Bühler’s RC 1.1 and RC 1.2 sample gas coolers are available with Modbus RTU.

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