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Streamflo Velocity Meter

The Streamflo series of instruments are used to measure, indicate and record very low velocities of water and other conductive fluids. Designed primarily for laboratory and specialised industrial use, the miniature head of the flow sensing probe can be inserted into small ducts and channels where it has the ability to measure velocities as low as 5.0 cm/sec. It is thus suitable for measuring accurately the velocities in hydraulic models of river estuaries, dams, harbours, etc., in addition to field measurements of clean water flows.

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Using indicator model 430, a completely portable system requiring no mains supply is available. This is ideal for carrying around from one measuring point to the next. The use of two probes allows the range of detectable flow rates to be extended up to 300 cm/sec. All components have been chosen carefully to give long reliable life with the minimum changes in calibration within the operating temperature range stated under specification. The sensing probe was originally designed by the British Department of Scientific and Industrial Research. Further development by Nixon Flowmeters has resulted in a compact system offering digital indication with optional recording facilities.

Operating Principle

Operating Principle:

The sensing probe is a measuring head joined by a slim tube to the plug and socket which connects to the measuring instrument.

The measuring head comprises a five bladed PVC rotor mounted on a hard stainless steel spindle, itself terminating in fine burnished conical pivots which run in jewels mounted in a shrouded frame. Minimum frictional resistance is thus ensured. An insulated gold wire contained within the tube terminates 0.1 mm from the rotor blade tips. When the rotor is revolved by the movement of a conductive liquid, the passage of the rotor blades past the gold wire tip slightly varies the measurable impedance between the tip and the tube.

This variation is used to modulate a 15 kHz carrier signal, generated within the indicating instrument which in turn is applied to the electronic detector circuits. All components have been chosen carefully to give long reliable life with the minimum changes in calibration within the operating temperature range stated underspecification.


Automatic compensation is made for changes in liquid conductivity. Following amplification and filtering out of the carrier frequency, a square wave signal is obtained. In the digital indicator the pulses are counted over a known time period to obtain a digital reading.

4O3 Standard low speed velocity probe for the range 5.0 to 150 cm/sec.
4O4 Standard high speed velocity probe for the range 60 to 300 cm/sec.
Fitted with streamlined fairing to provide additional mechanical strength and freedom from turbulence at higher velocities.
150 cm/sec.
423 90 Degree angles probe to measure vertical velocities over the range 5.0 to 150 cm/sec

With all probes, increased immersion depths can be provided to special order. The maximum length of probes is only restricted by shipping constraints. Sealed probe/cable connectors have been supplied to enable immersion of the cable and probe assembly.