SOLUTION SHEETMiniCTA and Multichannel CTA

Compact CTA Systems for accurate flow investigations

The Multichannel CTA (top) and the MiniCTA (below)

Introduction
The MiniCTA and Multichannel CTA systems are solutions for educational and industrialuse. They can be used for applications in air (up to 100 m/s) and in water (up to 2 m/s)
and can be used with both wire and fiber/film probes depending on the application. Theyare especially suited for multipoint measurements in boundary layer investigations or instudies of coherent structures.

Key benefits•Bandwidth ~10 kHz for wire probes in air•

Up to 20 m cables can be used•

Easy to use and easy to learn software – calibration, data acquisition, traversing, datareduction,reduction,databasedatabaseandandgraphicalgraphicaldisplay
displayininaasingle
singleplatform
platform•

Velocity and directional calibration of probes•

Various Calibration Systems ensuring high accuracy

CTA and its application areas
Constant Temperature Anemometer (CTA) technology is a well-establishedtechnique with commercial systems available since 1958. The measurement
principle is based on the cooling of small sensors placed in a flow.
The temperature (resistance) of the sensor is kept constant by an advanced
feedback control loop that contains an electronic bridge circuit. This way, theanemometer produces a continuous voltage that is directly related to theinstantaneous flow velocity. The output signal is sampled with high enoughresolution to analyze the fluctuations in the frequency domain.
Even though CTA technique is intrusive and non-linear in response, it is still
the best instrument for the accurate determination of high frequency flow
fluctuations, turbulence investigations, boundary layer diagnostics, andsimultaneous multi-point velocity and temperature measurements.

MiniCTA and Multichannel CTA Solutions
The MiniCTA and Multichannel CTA systems offer cost-effective solutions formeasurement of flow and turbulence in air applications with up to 100 m/s
velocities and up to 10 kHz fluctuation frequencies, or water applications up to 2m/s.
Both platforms contain the same circuit board and therefore share the same
specifications for velocity channels. The MiniCTA system is the single-channel
version and is ideal for new CTA users and for more experienced users needingmobility. The MiniCTA system is also well suited for demonstration of CTA inundergraduate fluid dynamics laboratory classes.
Multichannel CTA systems offer more functionality than their single-channel
counterparts. They are normally configured with a number of velocity
channels and a temperature channel, allowing for temperature correctedvelocity measurements. Both systems are operated by the StreamWare Basic
software, which supports set-up, probe calibration (both velocity and directionalcalibration), data acquisition, data conversion and data reduction.

MiniCTA
MiniCTA is a single channel anemometer optimized for measurements in air up
to 100m/s and in water up to 2m/s. The frequency bandwidth reaches above
10 kHz at 50 m/s in air. The unit is also designed for use with probes suited forwater applications.
MiniCTA

MiniCTA system shown with Calibrator and Directional Calibrator

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Multichannel CTA
The multiple-channel versions of the MiniCTA offer a cost-effective solution
for multiple-sensor measurements. Multichannel CTA systems are available
in three different versions: with 4, 6 and 8 channels. The 4-channel, and the8-channel versions contain just velocity channels. The 6-channel version
contains 6 velocity channels, a temperature channel used with a thermistor
probe for temperature correction and a channel for an optional reference
velocity for in-situ calibrations in wind tunnels.
Multichannel CTA

Multichannel CTA system. A calibrator can be added for calibrating one probe at a time.

Probes
Our standard hot-wire and hot-film probes are supported by the MiniCTA andMultichannel CTA systems, and cover most applications in flow measurements.
Additionally, special probe and support designs for unique flow situationsin accordance with customer’s specifications can be offered upon request.
Contact your Dantec Dynamics representative for more details.

Probe supports, mounting tubes and cables
Probe supports connect the probe electrically to the CTA module while
supporting it mechanically. They are available for all standard probes instraight and right-angle configurations. Mounting tubes made of stainlesssteel can extend the reach and stiffness of the probe support.

Hot-wire and hot-film probes

A/D Converter

The output voltage from the CTA channel must be converted to a digital value
for analysis in the software.
A 4-channel USB A/D converter with max. 100 kS/s simultaneous sampling isused with up to 4 MiniCTA channels or MiniCTA Temperature Module. With USB
interface for the A/D converter, the system can be operated from a laptop.
For the Multichannel CTA, both USB and PCI board A/D converters areavailable.

SoftwareStreamWare Basic is a complete software package running in a Windows
environment that helps the user to design, organize and document themeasurements as well as post process the results.
The complete system can be controlled by StreamWare Basic, which supports
probe calibration, data acquisition, conversion and reduction. Raw and reduced
data can be presented in StreamWare Basic or exported to other applications(e.g. Excel® and Tecplot®) for further analysis.

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Velocity field in the wake of a cylinder.
Data exported from StreamWare Basicto Tecplot.

Database for organised measurements and results
StreamWare Basic organizes the measurement setups and stores them in a
dedicated database. The complete measurement task from configuration andexperiment layout to acquiring, reducing and storing data is performed in
an intuitive way. The user can go back to a data set and see the instrument
configuration, electronic settings, measurement chain, and analysis sequence
as an on-line notebook.
Default set-up parameters related to the actual probe are stored in dedicatedlibraries, as are drivers for a number of A/D converters and a traverse system.
StreamWare Basic can communicate with the automatic calibrator and a
traverse system via USB (or LAN), while analog data are being acquired via anA/D converter.

Block-averaged Power Spectral Density
in the wake of a 10 mm diameter cylinder at 10 m/s.

All set-ups, calibrations, experiment layouts and raw and reduced data are
saved by the StreamWare Basic project manager, which puts you in full control
and ensures traceability of results.

Turbulence Diagnostics in StreamWare BasicCTA is the preferred technique for investigation of turbulence due to its
unmatched frequency response. In the frequency domain, power spectra canbe computed for analysis of the fluctuating flow characteristics.

System Computer
The MiniCTA and MultichannelCTA systems can be delivered with a systemcomputer, a portable or a desktop version, which is preconfigured, tested andready to use. All necessary hardware and software installation is performed
before delivery.

System Test
All Dantec Dynamics systems with system computers have to pass a detailed
system test procedure before shipment where the test data is recorded on thesystem computer. The system test procedure ensures a smooth installation of
the system on site and a quick start to actual research activities.

The system computer is from an international manufacturer with worldwide
presence.

Options
MiniCTA temperature module
A compact thermistor and amplifier package is available for measurement ofslow temperature changes. With this package one can perform temperaturecorrection to improve measurement accuracy in flows with temperature
variations. The package is especially useful for stand-alone MiniCTA- (singlechannel) and MultichannelCTA systems without temperature channels (4-channeland 8-channel versions).

Velocity calibration
As the sensor response depends on many external factors other than velocity,a calibration is often required for accurate CTA measurements. We offer
calibrators for velocity calibration in air to assure high accuracy at all times.
Calibrators are available in manual and automatic versions. Both calibrators
are designed for calibration of wire and fiber-film probes in air at velocities
from a few cm/s up to > 300 m/s. The probe is placed in a free jet with a flat,
low-turbulent velocity profile during calibration. The automatic calibrator isconnected to a computer via USB or Ethernet and the calibration process iscontrolled from StreamWare Basic software. The manual calibrator supports
a two-point as well as a multi-point calibration scheme. Both calibrators aresupported in the StreamWare Basic software.
Page 4Hotwire Calibrator for manual velocity
calibration.

The calibrators are delivered with certificates including the calibration
data of the internal transducers (traceable to accredited laboratories) anda verification of the jet velocity in three points over the velocity range. For
further details on the calibrators, please refer to the data sheets available atour website.

Directional calibration
Hotwire sensors have velocity, temperature and directional sensitivity. Multiple
sensor probes are used to perform 2- & 3- component velocity measurements
using the directional sensitivity. For accurate measurements, a directional
calibration should be performed using an optional manual Pitch/Yaw/Roll
Manipulator or Automatic Directional Calibrator. Both types of directional
calibrators fit to both types of velocity calibrators.
Individual velocity and directional calibrations improve the accuracy of themeasurement compared to experiments using standard pitch & yaw factors.
For further details on the directional calibrators, please refer to the data
sheets available at our website.

Manual Directional Calibrator mounted
on top of an automatic calibrator. It
allows probe rotation around two axes.

Calibrator fow water velocity
The water calibrator is a recirculating water tunnel with a submerged jet in awater reservoir in front of the jet. It covers velocities from 0.005 to 2 m/s. The
velocity is calculated on the basis of a flowmeter reading.
For further details on the water calibrator, please refer to the data sheet
available at our website.

Water calibrator for hot-film probes,
shown with the optional pitch/yaw/rollmanipulator.

Traversing systems
We offer traversing systems that can move the probe in one, two or three
directions with high accuracy. The traverse may be equipped with a proberotation unit that also allows probes to be rotated. The rotation may beneeded in order to obtain proper alignment of the probe with respect to theflow, or for obtaining three velocity components from single slanted wireprobes or x-probes. For further details on the traversing systems, please referto the data sheet available at our website.
Probe rotation unit

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Technical Specifications
Specifications

MiniCTA(54T42)Multichannel
CTA (54N82)

Multichannel
CTA (54N81)

MultichannelCTA (54N80)

Velocity channels

1468

Temperature channels--1-Max. output Voltage

0.05 - 7 Volt

Max. probe current

400 mA

Operating resistance range

4 - 36 Ohm

Freq. response

10 kHzEquivalent input noise

Typ. 3nV/ √ Hz > 1 kHz

DC Offset

0.9 - 2.2 Volt

DC Gain

2 - 5 Volt cont.

Max. probe cable length

20 m

Solution Sheet 0560_v1. Subject to change without notice. Copyright © 2020.
Dantec Dynamics. All Rights Reserved. www.dantecdynamics.com