Probes for Hot-wire Anemometry

Introduction General information This catalog describes the complete line of Dantec Dynamics’ standard hot-wire and hot-film probes for use with Constant Temperature Anemometers (CTA). The CTA anemometer is today’s most widely used instrument for measurement and analysis of the microstructures in turbulent gas and liquid flows. The output of the anemometer represents the instantaneous velocity at a point and forms the basis of a statistical analysis describing the flow conditions in that point, for example mean velocity, turbulence intensity etc. Its main features are: • Fast response. Fluctuations...

Gold-plated wires probes are available with one, two and three sensors (single, X- and tri-axial arrays) in six different configurations. Miscellaneous wire probes Temperature probe Fig. 1. 5 µm dia. plated tungsten wire, welded to the prongs. Fig. 2. 5 µm dia. plated tungsten wire, gold-plated at the ends to provide active sensor length of 1.25 mm. Fig. 3. 70 µm dia. quartz fiber with nickel film, gold plated at the ends to provide active sensor length of 1.25 mm. The Dantec Probe System The sensor materials are selected to provide maximum flow sensitivity and highest possible mechanical strength...

Film probes with cylindrical sensors (fiber-film probes) fiber probes are available in three configurations for work in free-stream flows, pipe flows and boundary layers. The standard versions are only for gas applications. for applications in gas and liquid flows. Fiber-film probes Fiber-film probes have cylindrical thin film sensors and may be used as a substitute for wire probes in liquids or in gas applications where more robust probes are needed. Fiber sensors are 70 µm diameter quartz fibers, 3 mm long, covered by a nickel thin film approx. 0.1 µm in thickness (Fig. 3). The ends are copper-...

Fig. 7. Sensor arrangement of X-probe. Sensor configurations The Dantec Dynamics probe system comprises probes with one, two or three sensors for measurements in one-, two- or three-dimensional flows. Normally, each probe type is available in a number of configurations with different prong or substrate bends. In this way it is possible to select the correct probe for almost any measurement situation. Mounts with the probe axis parallel to the direction of the mean flow. The probe is rotated to get the velocity components. (h) Glue-on probe. Determines the points of transition and separation and...

Fig. 10. Temperaturecompensated wire probe for slow temperature fluctuations. Fig. 11. Plug-in probe design. Dual-sensor probes Dual-sensor probes are designed for use in two-dimensional flows. The sensors are arranged in X-arrays or Varrays, where they form an angle of 90° with one another, or they are placed opposite each other on a cylinder surface (split-fibers). X-array wire and fiber probes All X-probes measure two velocity components simultaneously in turbulent, instationary two-dimensional flow fields. They provide information for calculation of Reynolds shear stress. The flow vector...

Fig. 13. Probe support for dualsensor probes. Fig. 14. Probe support for triplesensor probes. Fig. 15. Probe support for single-sensor probes. Sectional view. Miscellaneous dual-sensor probes glued into a stainless steel tube that mounts axially in the 6 mm body. Outside diameters for probe supports are 4 mm and 6 mm for single- and dual-sensor probes, respectively. The cables on dual-sensor supports are marked with one and two rings indicating the connector number corresponding to the sensor number on the probe. Temperature-compensated probe Temperature changes in the medium under investigation...

Probe selection chart MEDIUM STATE OF MEDIUM Fiber-film Triple-sensor probes Fiber-film X-probes and Split-fiber probes Glue-on probes Flush-mounting probes Conical probes Fiber-film probes Triple-sensor probes Parallel-sensor probes FILM PROBES Miniature X-probes Gold-plated X-probes Temperature-compensated probes Resistance thermometer Miniature wire probes Gold-plated wire probes WIRE PROBES Gases and non-conducting liquids Conducting liquids Low and medium temp. up to 150°C Contaminated flow Extremely low velocities FLOW CONDITIONS Low and medium velocities High velocities Large velocity...

Fig. 18. Typical square wawe test for 0.5 µm wire probe. Recommendations for use Mounting and adjustment Avoiding ground loops and noise pickup BNC connectors on probes, probe supports and probe cables must not be in contact with any metallic part of test rigs or mounting systems. BNC connectors on dualand triple-sensor supports must not touch each other, as this will disturb the operation of the individual CTA servo-loops in the anemometer electronics. Grounding in liquids The liquid must be grounded as close to the probe as possible by means of e.g. an electrode plate connected to the signal...

Maintenance and repairs Control and testing at Dantec Dynamics Each probe is thoroughly controlled and tested at Dantec Dynamics before it is shipped to the customer. The control includes a visual inspection of sensor dimensions and check of mechanical strength and electrical properties. Finally the probes are tested in a CTA anemometer under normal operating conditions. Film probes for use in conducting liquids are operated in running water for several hours. The insulation of the protective quartz coating is tested in a sodium chloride solution (3%) by applying a voltage across it. All probes...

Technical reference Summary of technical data Sensor material The standard sensor materials are selected on the basis of the most common applications. The following property values are of importance when selecting sensor material: The TCR is therefore measured for each individual film probe and written on the probe label. temperature coefficient of resistance α0 (TCR): RT = R0·(1 + α0·(T - T0)) Lead resistance The lead resistance RL is the internal probe resistance defined as the resistance between the sensor and the connector pins (or BNC connector) on the probe. All values given in the technical...