DFT - Compact Paddle-Wheel Flow Sensor

What Is the DFT Compact Paddle Wheel Flow Sensor?

The KOBOLD DFT is a compact paddle wheel flow sensor for water and low-viscosity liquids. An inlet nozzle directs flow onto the paddle, so it needs no straight pipe runs. It is a smaller, more economical version of the DF series, with a nickel-plated brass or PTFE body and five ranges from 0.05–0.50 GPM to 0.8–15 GPM. The DFT is made in the USA.

The paddle carries a sealed ring magnet that transfers its rotation, without contact, to a Hall sensor mounted on the housing. The Hall sensor outputs a frequency signal proportional to flow rate. An open collector pulse output is standard. Optional KOBOLD electronics can display that signal, convert it to a 4-20 mA or 0-10 VDC analog output, totalize it, or switch up to two limit contacts.

DFT Flow Ranges, Connections, and Accuracy

The DFT comes in five measuring ranges, 0.05–0.50, 0.13–1.8, 0.26–4.0, 0.5–9.5, and 0.8–15.0 GPM, each set by a fixed inlet orifice of 2.0, 4.3, 5.9, 9.0, or 13.5 mm. Accuracy is ±2.5% of full scale, or ±5% on the standard OEM pulse output version (DFT-..0000). Female process connections are 1/4", 1/2", or 3/4" NPT, or G1/4, G1/2, or G3/4, offered by range.

Pressure loss at maximum flow is 8.7 to 11.6 PSI for brass housings and 7.25 to 13.0 PSI for PTFE housings, by measuring range.

Brass or PTFE Body: Which DFT Fits the Liquid?

The nickel-plated brass DFT is designed for water, light chemicals, and low-viscosity liquids below 10 cSt, and is rated to 230 PSIG. The PTFE version is designed to stand up to aggressive chemicals and is rated to 70 PSIG. Both versions operate from -4°F to 176°F (-20°C to 80°C).

Construction materials:

• Housing and cover: brass or PTFE
• Vane: PTFE
• Axle: ceramic (Al2O3) or sapphire
• Bearing: PTFE
• Gasket: NBR (DFT-31/36 models) or FEP-O with silicone (DFT-33/38 models)
• Front and back panels: black-anodized aluminum (DFT-33/38 only; non-wetted)
• Screws: stainless steel

DFT Output and Electronics Options

Every DFT ships with a pulse output, and the same sensor body accepts optional electronics for analog transmission, switching, rate display, totalizing, or batching. All versions carry IP65 electrical protection. The options, with their supply and connection details, are:

• Standard OEM pulse output (..0000): NPN open collector, 5-24 VDC supply, 15 mA maximum sink current, DIN 43650 plug.
• Pulse output F400: PNP open collector, 24 VDC ±20% supply, 20 mA maximum, DIN 43650 plug.
• Analog output L443 or L442: 4-20 mA, 3-wire or 2-wire, 24 VDC ±20% supply, 500 Ω maximum load, DIN 43650 plug.
• MA electronics: 4-20 mA or 0-10 VDC output, 500 Ω maximum load, 24 VDC or 110 VAC supply, 1.5 m (4.9 ft) cable or connector.
• WM electronics: one SPDT switching contact rated 250 V / 5 A maximum, 24 VDC or 110 VAC supply, 1.5 m (4.9 ft) cable or connector.
• K electronics: 8-digit backlit LCD rate display, 4-20 mA or 0-10 VDC analog output, minimum and maximum SPDT contacts rated 24 V / 2 A, 2.5% hysteresis, 24 VDC supply, 1.5 m (4.9 ft) cable.
• E totalizer electronics: 2-line, 8-digit backlit LCD showing rate, total, and grand total, 4-20 mA or 0-10 VDC output, two relays rated 30 V / 1.5 A, 24 VDC supply, 10-pin cable or two M12 connectors.
• G batching electronics: as the E version, with batch, start, stop, reset, fine batch, and correction quantity functions.

Installing the DFT: No Straight Runs, Any Orientation

Because the inlet nozzle directs flow onto the paddle, the DFT needs no upstream or downstream straight piping and can be mounted in any orientation. Mount it tension-free and check the union fitting seals after installation. Exceeding the measuring range by more than 20% can damage the bearing, so confirm the actual flow against the label.

Introduce the liquid slowly at start-up, and keep the housing continuously filled during operation. Pressure surges from solenoid valves, ball valves, or similar devices (water hammer) can break the instrument, and large air bubbles can cause measuring errors or bearing damage. Contact versions should not be installed within an inductive field. Before wiring, confirm the supply voltage and de-energize the supply wires; incorrect plug wiring can destroy the electronics.

Common Questions about DFT - Compact Paddle-Wheel Flow Sensor