DOG Oscillation Flow Meter for Wet and Dry Gases
The KOBOLD DOG is an oscillation flow meter for gases that measures volumetric flow with no moving parts. Two versions are offered: the DOG-4 for dry gases and the DOG-6 for wet, damp, or moist gases, with an angled measuring head that drains condensate. ANSI flanged sizes from 1" to 8" cover 0.07 to 3,500 CFM of air.
How the Oscillation Principle Works
Gas passes through an orifice in the meter body, and the dynamic pressure at the orifice pushes part of the flow into bypass bores at the sides. That division ratio stays constant over the whole measuring range, so the oscillation measured in the bypass reflects the total volume flow through the meter.
In the bypass, a gas column swings left and right in a U-shaped channel at a frequency proportional to flow velocity, and a platinum sensor detects it. The flow channels are large enough that constant changes in direction produce a self-cleaning effect, so the DOG is extremely dirt resistant and has no consumables. It is designed for low maintenance, long-term stability, and low pressure loss.
DOG-4 vs. DOG-6: Dry Gas or Wet Gas
Choose the DOG-4 for dry gases and the DOG-6 for wetter gases such as biogas. The DOG-6 adds a special sensor construction and a measuring head angled at 2.7°, so condensate drains out of the measuring chamber instead of collecting in it. The DOG-4 offers a 1:100 span, and the DOG-6 offers up to 1:75.
Ranges are stated for air and listed by full-scale value as DOG-4 / DOG-6. Sizes 1" to 4" come in Class 150 or 300; 6" and 8" come in Class 150.
- 1": 7 to 41 / 5 to 32 CFM
- 1½": 7 to 120 / 5 to 88 CFM
- 2": 7 to 150 / 5 to 110 CFM
- 3": 82 to 470 / 62 to 350 CFM
- 4": 160 to 590 / 120 to 440 CFM
- 6": 350 to 1,800 / 270 to 1,300 CFM
- 8": 710 to 3,500 / 530 to 2,400 CFM (DOG-4 calibrated to 2,400 CFM; higher on request)
Gas Applications
The DOG is used to measure compressed air, natural gas, biogas, digester gas, fermentation gas, propane, hydrogen, nitrogen, and argon. Measured gases must be compatible with the materials of construction. For wet gases such as biogas, the DOG-6 is the version to specify, since its angled head lets condensate drain.
Specifications and Ratings
Accuracy is ±1.5% of reading in the upper part of each range and ±5% of reading near the bottom, with 0.1% of reading repeatability. Maximum operating pressure is 230 psi (15.9 bar) regardless of flange size or class, and the sensor is rated IP65.
- Media temperature: -4 to 248°F (-20 to 120°C) standard, -4 to 140°F (-20 to 60°C) for ATEX versions
- Ambient temperature at the sensor: -4 to 176°F (-20 to 80°C) standard, -4 to 140°F (-20 to 60°C) for ATEX versions
- Materials: 316L stainless steel housing and orifice, polyphenylene sulfide (PPS) measuring head, platinum/PEEK/ceramic hot wire sensor, Klinger SIL® C-4265 and NBR gaskets, stainless steel ball valves
Hazardous Area Approvals
ATEX and IECEx certified versions are available for hazardous locations. The certified sensor (II 1 G Ex ia IIC T4 Ga) can be used in Zones 0, 1, and 2 in explosion groups IIA, IIB, and IIC, while its transmitter ([Ex ia Ga] IIC) is installed outside the Ex area.
Electronics and Outputs
Every DOG sensor connects by cable to its own matched transmitter, located up to 164 ft (50 m) from the sensor. Three electronics families are offered, from a simple frequency output to a flow computer, with 110 VAC versions of each and 24 VDC versions of the first two.
- Frequency output: opto coupler output with frequency linear to flow, DIN rail mounted, IP20
- Unit counter: backlit LCD with flow rate and totals, 4-20 mA (active, 3-wire) and PNP pulse outputs, wall mounted, IP65
- Flow computer: adds compensated flow rate and total from a PT100 temperature input and a 4-20 mA pressure input (sensors not included)
Installation Guidelines
The DOG can be mounted in any position. When condensate forms in the gas, mount it horizontally with the sensing element pointing up. Provide a straight run of 10 pipe diameters upstream and 5 downstream, and keep the gas velocity anywhere upstream below the speed of sound.
Insulate the pipe and meter when ambient and gas temperatures differ by 36°F (20°C) or more, and open shut-off valves slowly at startup to protect the sensor.
Sensor Replacement and Maintenance
Optional bypass ball valves between the measuring head and housing allow sensor replacement and measuring head cleaning without interrupting flow in the main line or the meter body. They also protect the sensor against mechanical damage during startup. Spare sensors and an oscillator sealing set are available as accessories.
Common Questions about DOG - Oscillation Flow Meter for Gases
The DOG works as an oscillating beam device with no movable parts. An orifice plate in the base creates flow resistance that forces a partial flow into the oscillator, where the gas begins to oscillate. Because that partial flow keeps a fixed ratio to the total, the frequency read by the platinum sensor tracks the entire volume flow.
Between 1% of range and a transition point called Qt, accuracy is ±5% of reading; from Qt to full scale it is ±1.5% of reading. Qt drops as gas density rises, from 8% of range at 0.062 lb/ft³ (1 kg/m³) to 1% of range at 0.50 lb/ft³ (8 kg/m³) and denser.
Use the DOG-6. Its sloped measuring chamber and special sensor build let condensate run off while wet gas is measured. For damp media, install it with a slight incline in the flow direction and add a condensate separator upstream. Dry gas service calls for the DOG-4, which has a wider 1:100 span.
All flange sizes and classes are limited to 230 psi (15.9 bar). Standard models accept gas from -4 to 248°F (-20 to 120°C) with ambient conditions up to 176°F (80°C). ATEX models are restricted to -4 to 140°F (-20 to 60°C), covering both the gas and the surrounding air.
Plan for 10 diameters of straight pipe on the inlet side and 5 on the outlet side. Fitting a flow straightener upstream is recommended to prevent rotational flow. Gas velocity ahead of the meter must remain subsonic, and both pulsating streams and pressure drops above critical should be avoided.
Yes, on meters ordered with the two optional ball valves. Closing them isolates the measuring head, so the hot wire sensor can be swapped while gas keeps moving through the pipe. On meters without ball valves, shut off the gas and discharge line pressure first, then remove the sensor and replace its O-rings.
If no light is on, check the supply voltage and power terminals. Green OPERATING with no output signal points to the output terminals. Yellow RANGE means flow is above or below the measuring range. Red ERROR means a short or break in the sensor circuit; a working hot wire sensor reads 40 to 75 Ω.
The basic transmitter delivers a frequency signal through an opto coupler. Unit counter and flow computer models add an active 4-20 mA analog signal, a PNP pulse output scaled to the linearized total, and a display. Both can be fitted with Modbus RTU over a 2-wire RS485 link.
Yes. With ATEX or IECEx certification, the sensor is intrinsically safe (Ex ia) and suited to gas Zones 0, 1, and 2, including explosion group IIC gases. The transmitter must stay outside the Ex zone, connected by a measuring cable no longer than 164 ft (50 m).
Product Specifications
Range
0.07...7 to 35...3,500 CFM (Air)
Fittings
1"...8" ANSI Flange
Wetted Materials
Stainless Steel
Maximum Temperature
248°F (120 °C)
Accuracy
± 1.5 % of Reading
Output
Analog, Pulse, Flow Computer
Product Features
Unique Flow Meter Technology
Sloped Design Drains Condensate from Moist Gas
Low Maintenance, High Longevity
Ideal for Biogas, Digester Gas, Fermentation Gas, Compressed Air, Nitrogen, Argon and More
Certifications/Approvals: ATEX, IECEx
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