Data Acquisition

Computerized Data Acquisition (DAQ) System

DAQ is a process of sampling signals that measure real-world physical conditions and converting the resulting samples into digital numeric values that can be manipulated by a computer.
- the process of collecting information using sensors, measurement devices, and a computer.
- It has 8 channels for input signals

MUX

multiplexing, an electronic switch using which the computer reads information from various channels one at a time.

Signal types

Digital:
- on/off (TTL line)
- pulse train (Counter/timer)
Analog:
- DC (ADC/DAC - slow)
- Time Domain (ADC/DAC -fast)
- Frequency (ADC - fast Analysis)

Number Representation

Decimal (Base 10) and Binary (Base 2)
8 bits = 1 Byte
8bit number: 0 to 255

Negative decimal numbers in binary

represented by Two's Complement

Resolution

the number of pixels per square inch on a computer-generated display; the greater the resolution

Digitization

sampling + quantization

Aliasing

Occurs due to under-sampling.

Nyquist Theorem

No analog signal must have frequencies greater than half the sampling frequency.
Fmax <= 0.5 SF
- if the condition is not met, digital frequency is not a true copy of the analog frequency therefore aliasing occurs

range and resolution

the smaller the range the better the resolution

quantizing error

occurs when analog inputs converts to the digital value

Analog-to-Digital Converstion (ADC)

converts raw audio signal into digital signal for storage
- number of bits used to represent the signal
- input range - unipolar/bipolar

Unipolar/Bipolar Input range

For a unipolar ADC with differential inputs, the positive input swings from zero-scale (the negative input) to positive full-scale (with respect to the negative input). The term "bipolar" indicates that the signal swings above and below some reference point.

Digital-to-Analog Conversion (DAC)

converts digital signal to analog signal that travel to speaker/headphones as electrical current

Amplification

(range/resolution) action of taking out smaller signals as they exist in transducer and making them larger

Single-Ended Measurement

measuring one potential with respect to a fixed common reference
- create noise

Differential Measurement

transmits electrical signals using two complementary signals