MAE 322
Thermal and Fluids Laboratory
Introduction to Data
Acquisition
DATA AQUISITION
• What is a data acquisition (DAQ) system?
o Electronic hardware that ensures the communication
between various sensors and a recording computer
• Why do we need DAQs?
o Record measurements from various sensors
o Record measurements at a certain speed (data rate)
o Ability to control devices
• What do DAQs do?
o Analog inputs: DC volts of various ranges output by a
sensor is measured
o Analog outputs: DC volts output to a device for
control purposes
o Digital outputs: 0 or 1 (Boolean output) that act as a
switch.
DATA AQUISITION
Labjack U6
NI USB-6001
ICP-PET 7019Z
• DAQ systems are usually combined with a computer program
that will establish communication between computer and DAQ
• The software will record the data in an appropriate file format
• We will use WVU CAFEE software “Scimitar” to communicate
with our DAQ systems
DATA ACQUISITION RATE
• Data acquisition rate is the frequency at which each data point
is acquired and stored
• Different systems have different capabilities
o High speed DAQ can capture data at MHz
o Typical DAQs can capture data at 10 Hz
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“sec”
• A 10 Hz data rate means a data point is retrieved and stored
every 1/10th of a second.
• We choose our DAQ based on how fast we need to capture the
data
• Sometimes we need DAQs that can work at kHz or MHz for
capturing high speed operation
MEASUREMENT DEVICES
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Pressure Measurement
Piezo electric transducers
o highly sensitive measurement
such as combustion pressure
Diaphragm transducers
o Atmospheric pressure
o Fluid or gas pressure
o Differential transducers
Output
o Milli volt (mv) or volts (V)
Supply Voltage
o DC voltage supply
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In this lab
Omega PX-120 series diaphragm
o Milli volt response
o 10mV response per voltage
supplied
o We will power the transducer
using a 5V DC supply, hence
maximum response is 50 mV
Omega PX274-30DI Series differential
pressure transducer
o 12-35 VDC power supply
o 0-5 VDC output
o Used to measure pressure
across orifice or pitot tube
application
MEASUREMENT DEVICES
Temperature Measurement
Thermocouple
o Based on the principle of seebeck effect
o Junction of two different conductors at kept at two different temperatures will
produce a current that is proportional to the temperature difference.
o Depending on combination of conductors, different type of thermocouple are
available
K-type
Courtesy: https://www.blazeprobes.com/types-thermocouples-temperature-rangescolor-codes/
MEASUREMENT DEVICES
Temperature Measurement
RTD
o Change in resistance due to temperature
o Designed for temperatures below 400°C
o More accurate than a thermocouple (0.1°C vs 1°C)
o Cost more than thermocouple
o Better linearity and more stable readings than a thermocouple
Courtesy: https://www.blazeprobes.com/types-thermocouples-temperature-rangescolor-codes/
MEASUREMENT DEVICES
Flow Measurement
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Rotameter
o Variable area flow meter with a float to indicate flow rate
o Visually record flow meter
Positive Displacement Pump (PDP) flow meter
o Highly accurate
o Mechanical counter will register the speed of rotation to calculate flow
rate
Flow Obstruction Meter
o Orifice, Venturi
Pitot Tube Flow Meter
o Averaging Pitot Tube calculates flow velocity and converts to fluid flow
rate
Advance Flow Measurement
Ultrasonic measurement
Coriolis Flow meter
Mass flow meters
Courtesy: https://www.sierrainstruments.com/products/50series.html
CALIBRATION
What do we mean by Calibration of a sensor?
• Converting sensor output to engineering units
• Sensor output is mostly in the form of voltage or current, we have to
typically reference this output against a known value to derive an
equation
• Sensor response can be linear (straight line) or non-linear (curved)
Pressure
(psig)
0
200
Sensor
Output
(mV)
0
50
Where do we find the reference?
• NIST traceable standard
NIST Standards
NIST: National Institute of Standards and Technology
• There is a standard for all measurement
• Time is monitored by atomic clock in NIST lab in Boulder, CO
• Standard for length is kept in International Bureau of Weights and
Measures in Paris (A bar made of 90% Platinum and 10% Iridium)
In labs we use NIST calibrated reference equipment for calibrating sensors
• Heise for pressure
• Fluke Thermocouple calibrator
• Laminar Flow Element for flow
Heise
Meriam LFE