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Ratio control

With a gas mass flow controller, you can easily dose a predefined flow. The units can measure the flow but also have an integrated control valve and a PID controller. You basically tell the unit what flow rate you like to have and the integrated micro-processor reads your desired flow and measures the actual flow. The system will than control the proportional integral valve so that the flow is equal to your setpoint.

If you have two of these units you can create a predefined gas mixture. The relation between these two gases maintains a certain ratio and therefore it is called a “ratio control”. The term master-slave control is often use in these kinds of applications, basically you give a setpoint to the Nitrogen MFC and the Ethylene set it setpoint depending on what the “master” measures. It is so adjusted that the Ethylene flow is in this case always 4% of the gas flow. The control can take place analogue or digital over Modbus (PLC or Vögtlin software on a PC)

Why Vögtlin MEMS mass flow controllers?

 A thermal mass flow controller is in principle based on the cooling effect of a gas over a heated sensor. Because of this principle the units dose the mass flow. Mass flow is independent of temperature and pressure changes; therefore, the system is independent of pressure and temperature. Beside that the MEMS technology is famous for its long-term stability, the units do not drift, are reliable and cost effective.

Why

A ready-to-eat, ripe tomato should be red and not too firm. Ethylene ensures that the green pigment, chlorophyll, is broken down. At the same time, the red pigments, the carotenoids, and the proportion of fructose increase. Pectin’s, which provide firmness, are also broken down. The natural ripening of fruit depends on various factors. If left unchecked, the time window for harvesting tomatoes would be small and the losses would be high.

To prevent all tomatoes from ripening at the same time, the company Stoll fumigates part of the plantation with this Nitrogen/Ethylene gas mixture. The fumigated plants become ripe. This means that more tomatoes can be sold and a higher turnover achieved. There is no waste and fewer rejects and the customers get a solid healthy looking product, ready to be consumed. 

Conclusion

The MEMS technology used in the “red-y smart series” from Vögtlin offers high accuracy and fast response times. The quick and easy installation of the instruments has also contributed to the customer satisfaction. The project between Vögtlin and the company Stoll was engineered by PanGas, which already had very good experience with the “red-y smart series” from Vögtlin Instruments.