Data Acquisition (DAQ)1

Data Acquisition (DAQ)

Hardware and software

What is DAQ System?

• DAQ systems capture, measure, and analyze physical phenomena from the real world.

• Light, temperature and pressure are examples of the different types of signals that a DAQ system can measure.

• Data acquisition is the process of collecting and measuring electrical signals and sending them to a computer for processing.

• Electrical signals comes from Transducers.

What is DAQ System?The building blocks of a DAQ system includes:

1. Transducer: A device that converts a physical phenomenon such as light, temperature, pressure, or sound into a measurable electrical signal such as voltage or current.

2. Signal: The output of the transducer.

3. Signal conditioning: Hardware that you can connect to the DAQ device to make the signal suitable for measurement or to improve accuracy or reduce noise.

4. DAQ hardware: Hardware you use to acquire, measure, and analyze data.

5. Software: NI application software is designed to help you easily design and program your measurement and control application (LABVIEW).

What is DAQ System?There are two methods of communicating the measured signal to the computer

Sensors (Transducer)

Why Signal Conditioning• To measure signals from transducers, you must convert them into a form a

measurement device can accept.

• Common types of signal conditioning include amplification, linearization,

transducer excitation, and isolation.

What type of device to use?

The trade-off usually falls between

1- Resolution (bits) & Code Width

2- Sampling rate (samples/second)

3- Number of channels, and data transfer rate (usually limited by “bus” type: USB, PCI, PXI, etc.).

Resolution• Precision of the analog to digital conversion

process is dependent upon the number (n) of bits the ADC of the DAQ uses.

• The higher the resolution, the higher the number of divisions the voltage range is broken into (2^n), and therefore, the smaller the detectable voltage changes.

Resolution• An 8 bit ADC gives 256 levels (2^8) compared to a

12 bit ADC that has 4096 levels (2^12).

Time (ms)100 200150500

0

1.25

5.00

2.50

3.75

6.25

7.50

8.75

10.00

Amplitude(Volts)

16-Bit versus 3-Bit Resolution(5 kHz Sine Wave)

16-bit

3-bit

000

001

010

011

100

101

110

111

| ||||

Code Width• Code width is the smallest change in a signal that a

DAQ system can detect

• Calculated using the formula Code width

Where D is DAQ device input range and n is the resolution

• Larger resolution implies smaller code width and more accurate representation of the signal

Code Width

For example, a 12-bit DAQ device with a 0 to 10 V input range detects a 2.4 mV change, while the same device with a -10 to 10 V input range would detect a change of 4.8 mV.

Sampling Rate• The data is acquired by an ADC using a process

called sampling. • Sampling an analog signal occurs at discrete

time intervals. • The rate at which the signal is sampled is known

as the sampling frequency.

Sampling Rate• The sampling frequency determines the quality of the analog signal

conversion process.

• A Higher sampling frequency achieves better conversion of the analog signals.

• The minimum sampling frequency required to represent the signal should be at least twice the maximum frequency of the analog signal under test (this is called the Nyquist rate).

• If the sampling frequency is equal or less than twice the frequency of the input signal, a signal of lower frequency is generated from such a process (this is called aliasing).

Sampling Rate

• For accurate frequency representation:– Sample at least 2x the highest frequency

signal being measured.

• For accurate shape representation– Sample 5–10x the highest frequency signal

being measured.

Sampling Rate

What Type of Device to Use?

There are many types of data acquisition and control devices on the market. A few have been highlighted above.

DAQ Device Properties?

DAQ devices have four standard elements:

• Analog input (AI)• Analog output (AO)• Digital I/O (DIO)• Counter/Timers

DAQ Device Available in the Lab.

Low-Cost Multifunction DAQ for USB NI USB-6008

• Small and portable• 12-bit input resolution, at 10 kS/s• Built-in connectors for connectivity• 2 analog outputs (range 0 to 5 V)• 12 digital I/O lines• 8 single ended inputs (4 differential inputs)• Input range ±1 to ±20V• The NI USB-6008 and NI is ideal for students.• 32 bit counter• 5 mA Output current drive

Around KD. 50


• NI USB-6008 Pinout

Similar DAQ.

Low-Cost Multifunction DAQ for USBNI USB-6009

14-bit input resolution, at 48 kS/s


M Series Multifunction DAQ NI USB-6211• 16 analog inputs single ended inputs (8 differential

inputs);(16-bit, 250 kS/s); Input range ±10 V• 2 analog outputs (16-bit, 250 kS/s); Output range ±10 V • 4 digital inputs • 4 digital outputs• 32-bit counters • Output current drive ±2 mA

KD 210


NI USB-6211 Pinout


M Series Multifunction DAQ NI USB-6259• 32 analog inputs (16-bit); 1.25 MS/s single-

channel (1 MS/s aggregate) Input range ±10 V• 4 analog outputs (16-bit, 2.8 MS/s) output

range ±10 V• 48 digital I/O (32 clocked)• two 32-bit counters• OUTPUT Current Drive is (Channel/Total)5 mA/20 mA

KD 510


NI USB-6259 Pinout


NI USB-9215A• 4 analog input channels of (16-bit) • Sampling rates at 100 kS/s per channel

KD 200


NI USB-9211APortable USB-Based DAQ for Thermocouples

4 channels of 24-bit thermocouple input

Compatibility with J, K, R, S, T, N, E, and B thermocouple types

KD 160


E Series devices:6024E, and 6251Eboth DAQ:

16 channels (8 differential) of analog input ±10 V

Two channels of analog output ±10 V

For 6251E: 32 lines of digital I/O; (16-bit); 1.25 MS/s; 100-pin connector. Output current drive is 5 mA per channel; Two 32-bit counters

For 6024E: 8 lines of digital I/O; (12-bit); 200 KS/s; 68-pin connector Output current drive is 5 mA per channel; Two 24-bit counters

6024E

6251E

Analog Input

• Signal Sources: A transducer may either be a grounded signal source or a floating signal source. Knowing which type is critical for making your measurement correctly

Analog Input• Input Modes:The devices have three different input modesDifferential (DIFF) input.Referenced single-ended (RSE)Nonreferenced single-ended(NRSE)

• The single-ended input configurations provide up to 16 channels.

• The DIFF input configuration provides up to eight channels.

Differential (DIFF) Input• Neither of the inputs of a differential measurement system are

tied to a fixed reference.

Differential (DIFF) Input

• A channel configured in DIFF mode uses two analog input lines. One line connects to the (ACH#+) of the device, and the other connects to the (ACH#-)

• The ground of the input circuit is connected to AIGND (analog input ground) pin of the DAQ

Referenced single-ended (RSE) Input

• A referenced single-ended (RSE) measurement system measures voltage with respect to the ground, AIGND, which is directly connected to the measurement system ground.

Referenced single-ended (RSE) Input

Since the input signal and DAQ system has the same reference (AIGND), which is the earth (The reference of DAQ)

A channel configured in RSE mode uses one analog input line connected to the (ACH#+) of the device The negative input is internally tied to analog input ground (AIGND).

NonReferenced single-ended(NRSE)

• In a non-referenced single-ended (NRSE) measurement system, all measurements are made with respect to a single-node analog input sense (AISENSE on E Series devices), but the potential at this node can vary with respect to the measurement system ground (AIGND).

NonReferenced single-ended(NRSE)

• A channel configured in NRSE mode uses one analog input line, which connects to the (ACH#+) of the device. The negative input connects to analog input sense (AISENSE).

Analog Output

• Data written to the terminals DAC0OUTand DAC1OUT and the ground is AOGND

E Series 6024E device Accessories

1) CB-68LP I/O Connector BlockLow-cost termination accessories with 68 screw terminals for easy connection


2) BNC-2120 Connector• 8 BNC analog inputs.• 2 BNC analog outputs• 2 user configurable BNC inputs• 8 digital I/O lines with LED indicators• Function generator with sinusoidal, triangular and

TTL output.• Thermocouple jack and an IC sensor for

temperature measurement• Resistance measurement input

E Series 6024E device Accessories3) The SC-2075 is a desktop• Binding posts

– Three for ±15 V outputs– Two for 0 to 5 V outputs– Two for measuring analog signals or DC voltages

• BNC connectors– Two for analog inputs– Two for analog outputs– One for triggering

• Spring terminals– Eleven for analog inputs– Seven for analog controls– Seven for counter controls– Two for TTL-level power and ground signals– Eight for digital input/output (DIO) signal


4) NI ELVIS: NI Educational Laboratory Virtual Instrumentation Suite

• A custom-designed benchtop workstation and prototyping board to provide the functionality of a suite of common laboratory instruments

• provides the functionality of the following Arbitrary Waveform Generator (ARB) Bode AnalyzerDigital Bus Reader Digital Bus WriterDigital Multimeter (DMM)Function Generator (FGEN)Impedance AnalyzerOscilloscope (Scope)Two-Wire Current Voltage AnalyzerThree-Wire Current Voltag

AnalyzerVariable Power Supplies

How to Select DAQ Device & Accessories

1) Run the MAX program from the labviewsoftware by selecting Tools Measurement and Automation Explorer.

What is MAX?


2) Select “Devices and Interfaces” from the configuration column.


3) Choose the NI-DAQmx Devices and select the “PCI-6024E” or other if there.


4) Using right click on the PCI-6024E and select “property”. In the new window, where the RTSIcable tab select None while select CB-68LP or BNC-2120 in the Accessory tab then click OK


5) Open the Labview program, in the front panel select functions, input then select the DAQ Assistant icon.

How to Select DAQ Device(Input & Output Channels)

6) Select “Analog Input” so as to input your analog data to the computer and Labview.


7) We have 16 physical input channels from ai0 to ai15, select a channel like ai0.


8) Select your input voltage setup


9) Now make the connections and select test then Run to see the input voltage.


• Example

Verify your sound card and prepare it for use with a microphone

1. Prepare your microphone for use. Double-click the volume control icon on the task bar to open up the configuration window. The sound configuration window can also be found from the Windows Control Panel: Start Menu»Control Panel»Sounds and Audio Devices»Advanced.

2. If you do not see a microphone section, go to Options»Properties»Recording and place a checkmark in the box next to Microphone. This will display the Microphone volume control. Click “OK”.


3. Uncheck the Mute box if it is not already unchecked. Make sure that the volume isturned up.


4. Close the volume control configuration window.

5. Open the Sound Recorder by selecting Start»Programs»Accessories»Entertainment»Sound Recorder.

6. Click the record button and speak into your microphone. Notice how the sound signal is displayed in the Sound Recorder.


7. Click stop and close the Sound Recorder without saving changes when you are finished. Uncheck Mute


• Examples

Documents

Data Acquisition (DAQ)1