Mass-Stream® Series Ideal For Wet And Dirty Gas Streams

Bronkhorst UK 15/12/2008

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Based on a simple and robust through-flow design, the Mass-Stream® Series from Bronkhorst UK presents no obstructions to the flow path, has no moving parts and features very low-to-ultra low pressure drop across the instrument. These features make the Mass-Stream ideal for the mass flow measurement of dirty gases, wet gases and even a combination of the two. Furthermore, the minimal pressure drop prevents harmful liquid drop-out from condensing gases, thereby eliminating internal corrosion and increasing instrument life.

Typical flow measuring applications for the Mass-Stream series include biogas from land-fill sites and digesters, WF6, SiCl4 and other particulating or condensing gases, dirty exhaust gases from combustion processes, carrier gases for particle analysers and humidified powder carrier gases for pharmaceutical research. In addition, the straightforward design can be applied to such cost-sensitive applications as consumption metering for accounting or internal billing purposes, medical gas monitoring, burner ratio control, air flow control in paint spray lines, multiple gas mixing and gas generators.

Suitable for a wide range of gases and with standard pipe fittings between ⅛” OD and 20mm, the Mass-Stream D-62XX series can be calibrated between flows of 0.25 and 6000 Ln/min air-equivalent; it has a standard turn-down of 20:1, although this can be higher on application. When configured as a mass flow controller, a direct acting proportional solenoid valve is integrated directly onto the base-block, for regulating flows up to 500 Ln/min. Above this flow rate, a compact external valve is close-coupled to the meter body, taking flow control up to the 6000 Ln/min limit.

Options include an integrated flow display on all models, a range of readout systems for analogue instruments, and digital versions providing fieldbus interfaces. One possible configuration is the combination of an external potentiometer, on-board PID control and integral flow rate indication; whilst still providing an output signal for data logging, such an instrument represents a standalone solution, without the need for an external set-point signal.

As part of the Bronkhorst BV Group and manufacturers of the Mass-Stream brand, M+W Instruments was the first company to introduce direct flow measurement using constant temperature anemometry (CTA), the principle behind through-flow metering. Each meter consists of a metal base-block with a straight through-flow path and two stainless steel encased sensors protruding into the bore. One acts as a heater and the other a temperature probe with measurements being taken directly from the main gas flowpath.

A constant difference in temperature is created between the two probes and the energy required to maintain this, according to King’s Law, determines the mass flow rate. The pressure drop across the instrument is almost comparable to a straight run of pipe and is therefore negligible, although since a number of mesh screens are introduced to condition the gas flow profile, these can create a small pressure drop. Where a very low pressure drop is required, a special version can be built for ∆P down to 0.1 mbar.

In addition to analogue models, Mass-Stream flow meters and controllers are available in a digital format and, whilst still retaining the voltage or current output, these also offer RS232 and bus protocols, such as Profibus-DP, DeviceNet and Flow-Bus. The digital series is characterised by a high degree of configurability, high signal integrity and a host of additional on-board features, including the pre-loading of up to 8 calibration curves for different gases.

Mass-Stream instruments are configured with factory settings for a smooth response characteristic, with a nominal 2 second valve response to avoid overshoot of the actual controlled flow rate. If required, however, a combination of the digital board and freeware available from Bronkhorst UK allows the user to directly modify the PID and control settings to tune the instrument specifically for a faster set-point response, for preset valve-opening limits or, indeed, for scripted time/set-point menus.