Flowmeters measure the mass of gas

Thermal mass flow regulators and mass flowmeters for gases are now among the standard instruments used in industrial laboratory and production processes.

Because these devices measure the mass flow directly, without diversions in the form of measuring the flow speed or the volume, the measurement results can be transferred without elaborate conversions to reaction equations and formulations.

The special feature about the Smart-Trak generation of devices from Litre Meter, a flow measurement specialist, is that one and same device can be used for ten different gases, and without any shortfall in precision needing to be taken into account.

With the Dial-a-Gas function and the user-friendly interface for the pilot module, the operator can adjust the device on the spot for use with different gases, and even select other operating parameters.

The devices are calibrated in advance to the ten gases which are most commonly used in industrial sectors and laboratories in the fields of biotechnology and pharmaceuticals, as well as in analysis and research sectors as well.

If required, a device can also be calibrated to a special gas, as a departure from the ten standard gases, on the basis of the type of application.

The Dial-a-Gas function can be selected either by means of the pilot module, available as an accessory, or with the aid of a PC by means of the computer interface.

The incorporation of the Smart-Trak mass flowmeter in automatic systems and control circuits is extremely simple by means of the various different input and output signals available.

Suitable for both remote monitoring purposes as well as use as integrated components in analyzers and systems, Smart-Trak offers digital and analogue inputs and outputs without the need for elaborate cabling.

An RS232 interface is available, as well as two analogue outputs.

While it used to be necessary to have considerably expensive supply power units with +/- 5VDC outputs, these modern gas mass flow regulators are designed for supply voltages of 24VDC.

Modular design.

In the basic design, the regulator or flowmeter is available either with the directly-integrated electronics or with remote electronics units, which offers some major advantages with regard to the installation dimensions.

The pilot module, which is available as an accessory, a display and operating unit, is supplied either secured directly to the device electronics, or can be installed by the operator up to 15 metres away from the device.

This means that the very small and compact module can now replace the external control modules which used to be required.

For systems in which standard devices are required, the use of units without pilot modules is a good solution.

The adjustment and setting of the parameters is carried out either directly at the factory, or the device parameters can be programmed by the operator/system constructor by means of a PC, depending on its use.

The small structural dimensions of 25x75x125 mm also allow the operator to use the Smart-Trak as a direct replacement device for other makes.

The Smart-Trak regulating valve balances out relatively large fluctuations in operating pressure and temperature.

The operator can select between operating modes, such as valve closed, normal, and flush, via the pilot module or the interface. As well as that, the response behaviour for the different requirements and systems pressures can also be adjusted.

The device bodies, manufactured entirely out of stainless steel, are available for measuring ranges between 0 and 10Ncm3/min and 0 to 50NI/min.

Other construction sizes for higher pressure flows are in preparation.

These devices can be used for all clean gases, as well as corrosive and toxic ones.

Use in fermenters and bioreactors.

A typical area of use for mass flow regulators is the fermenter sector.

The function of these bioreactors can be optimised by the use of thermal mass flow regulators.

In fermenters, bacteria (cell cultures) are cultivated for the most widely-differing areas of application.

To achieve this, they are placed in nutrient solutions with the admixture of the most suitable possible gas atmosphere, favourable for the proliferation of the cell cultures.

The ideal gas atmosphere is composed of the exact mixture of oxygen, carbon dioxide, and air. The supply of this gas mixture is ensured by the use of mass flow regulators.

The exact gas mixture in this case ensures optimum growth and growth rates, making use of cell mutations or even the death of cell cultures.

The reference values for the devices are specified by a super-ordinated computer, and the mixing ratio is changed in accordance with the progress of the process.

A further automation step in such processes for the monitoring and adjustment of the optimum gas mixture is the parallel monitoring of the pH value and of the proportion of oxygen in the solution. The super-ordinated computer takes these measured values as the basis for calculating the correct gas mixture, and passes the corresponding reference values directly to the mass flow regulator.

The Smart-Trak is particularly interesting for the manufacturers of systems such as these.

Because the devices can be used for ten different gases, fewer different types and designs are needed.

The possibility of direct exchange of the devices between one other, as well as of replacing devices from other manufacturers, reduces the need to keep these items in storage.

Thanks to the small surface area of the regulators, there is no problem in using them to replace other devices, and no need either for major modifications to be made to the systems. The manufacturers of the measuring devices are themselves in a position to produce devices from stock, and can so supply them more quickly, something which was not possible previously because of the wide range of types needed in order to adjust calibration to a specific gas.

Because the operator can also adjust the measurement range with the Smart-Trak within the specified limits himself, keeping items in store and obtaining stocks has also been made much easier.

Applications in the pharmaceutical industry.

Another typical situation for the use of mass flowmeters is the screening of tanks and other containers in which reactive fluids are being held or processed.

Most organic fluids and oils react with the oxygen in the air and change their properties and characteristics as a result.

The standard solution for this problem is to screen the product with nitrogen.

To do this, the tank chamber is filled with nitrogen above the fluid, and a certain volume is constantly conducted through the upper part of the tank in order to ensure that any contact between the product and the oxygen in the air is avoided.

In many cases, it is entirely sufficient simply to monitor the pressure, but the use of flowmeters offers a number of advantages, such as the measurement and totalling of the volume of nitrogen consumed. With the use of two devices to monitor the inflow and outflow of nitrogen, leaks can be readily identified.

The nitrogen inflow can be specifically adjusted and regulated respectively, if more or less of the product is to be drawn off from the tank.

In the manufacture of glass ampoules and other glass containers for pharmaceutical and medical products, the gas mixture of the burner flames, composed of natural gas and air, needs to be monitored very precisely.

Automatic adjustment and regulating by means of thermal mass flow regulators leads to a substantial reduction in the wastage rate, as well as providing other advantages.

The regulating of very small mass flow volumes of less than 50NI/h, with fluctuating upstream or downstream pressures, can be achieved with no problem at all.

The enrichment of the combustion air with oxygen improves the combustion quality of natural gas and increases productivity on the manufacturing lines.

In this case, the oxygen is metered into the air by means of mass flow regulators, and in this situation the display devices and elements for specifying the reference values integrated in the device are of great advantage.