KOBOLD DOG-4 / DOG-6 Oscillation Flow Meter for Gases

Oscillation gas flow metering without moving parts for biogas and compressed air

The KOBOLD DOG-6 is an oscillation flow meter for wet gases such as biogas and fermentation gas, and the DOG-4 is the companion model for dry gases. The medium flows through an orifice in a tube; dynamic pressure sends part of the flow into a bypass that contains a fluidic oscillator. A gas column oscillates in a U-shaped channel, the frequency is proportional to flow velocity and so to volume flow, and a platinum sensor picks it up. There are no moving parts and no consumables.

The DOG-6 has a special sensor construction with an inclined measuring head that optimises condensate drain. KOBOLD lists compressed air, natural gas, biogas, fermentation gas, propane, hydrogen, nitrogen and argon, with a span of 1:100 for the DOG-4 and up to 1:75 for the DOG-6. The devices must not be used for unstable gases.

Technical specifications

DOG-4 and DOG-6 compared and ordered

The order example for the DOG-4 is DOG-42S0S50 0 A0 0: range and flange size and rating, then ball valve option and electronics code. The bypass ball valves sit between the measuring head and the housing so that a sensor can be replaced or the head cleaned without interrupting the line. When condensate forms, mount the meter horizontally with the sensing element pointing up.

Selection notes

Accuracy depends on gas density: lighter gases raise the lower limit Qt, so the usable low range is narrower for hydrogen than for compressed air. The flow computer electronics compensate to standard conditions, but the temperature and pressure sensors are not in the scope of delivery.

Confirm before ordering: the gas and its density at operating pressure, whether condensate is present, minimum and maximum flow in m³/h or CFM, the flange standard, the supply voltage and the required Ex rating.

How the fluidic oscillator principle helps in gas service

Turbine and rotary gas meters depend on bearings and rotating parts that wear, stick when dirty and can be damaged by pressure shocks. The DOG design has no moving parts in the flow path: the only component that reacts to the gas is the oscillating gas column in the bypass channel, read by a platinum hot-wire sensor. This makes the meter tolerant of start-stop operation, and maintenance is limited to inspecting and cleaning the measuring head. Because the bypass ball valves isolate the head from the main housing, that inspection can be done without depressurising and dismantling the pipeline.

Why the DOG-6 exists for wet gas

Biogas leaving a digester is saturated with water vapour, and condensate forms as it cools in the pipework. Liquid collecting in a measuring channel disturbs the oscillation and causes drift or dropouts. The inclined measuring head of the DOG-6 lets condensate run back out of the sensor area, which is why KOBOLD positions it for biogas and fermentation gas while the DOG-4 covers dry gases with the wider 1:100 span.

Installation guidance

• Provide straight pipe of at least 10 × DN upstream and 5 × DN downstream, as the datasheet recommends; elbows, valves and reducers close to the inlet distort the velocity profile.
• On wet gas lines, install horizontally with the sensing element pointing up, and provide condensate drains at low points of the pipework.
• Keep the gas velocity well below sonic speed; for very high flows choose the next larger flange size.
• When compensation to standard conditions is required, order the flow computer electronics and supply separate pressure and temperature transmitters, which are not included.
• In hazardous areas, route the sensor circuit through the intrinsically safe transducer and observe the reduced ambient limit of +60 °C for the ATEX version.

Applications in Oman and the GCC

Typical uses include compressed-air consumption monitoring in factories, where leakage audits often reveal large savings; biogas measurement at sewage treatment plants and landfill sites; natural gas sub-metering for burners and boilers; and nitrogen or argon distribution in fabrication and process plants. In hot climates the electronics should be shaded, because the standard ambient limit is +80 °C and the ATEX version is limited to +60 °C, and direct sun on a metal enclosure can raise the internal temperature well above air temperature.

RFQ checklist

• Model (DOG-4 or DOG-6) and the full order code if known.
• Gas composition, density, operating pressure and temperature.
• Minimum, normal and maximum flow.
• Line size, flange standard and pressure class.
• Electronics type, output signals, Modbus need and supply voltage.
• Ex requirement, ball valve option and quantity.

Documents and quotation

The KOBOLD DOG-4 / DOG-6 datasheet (edition 1/07-2026) is attached to this page. Browse our Flowmeters category for related instruments, or compare with the KROHNE ALTOSONIC V12 gas flowmeter.

For a quotation, send the gas, operating pressure and temperature, flow range, line size and flange standard, electronics code and ATEX requirement.