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Data Logging is collecting or gathering data over a period of time

How data can be collected:

Sensors are used to take readings or measurements at regular intervals of their environment.
The sensors could be collecting data on a wide range of things such as tempetarure, humidity, pressure, wind speed, water currents, electrical voltage, pH readings, etc.
The sensors may be either analog or digital. If they take analog readings, an Analog-to-Digital Converter (ADC) will be needed to convert the signal into digital data which computer can understand.
As the sensor takes a reading, the data is sent through a cable or wireless link to the data logger.
The data logger ususally stores the data for a period of time before sending it in a large batch to a computer which will process and analyze it.
A data logger is often a hand held battery operated device which has a large amount of memory.

Logging Interval:

Sound recording : Thousandth of a second
Heart beat: Tenth of a second
Oven temperature: Minutes
Outdoor temperature: Hours
Soil dampness: Days
Growth of plants: Weeks
Destruction of rain forest: Months
Movement of glaciers: Years
Melting of the ice cap: Decades

Advantages of Data logging:

Data logging can be used in remote and dangerous situations
Data logging can be carried out 24 hours a day, 365 days a year.
Data logging is often more accurate because there is no likelihood of human error.

Disadvantages of Data logging:

If data equipment breaks down or malfunctions, some data could be lost, corrupted or not recorded.
Equipment can be expensive even for a smaller task.
The equipment can take readings only at a logging interval which has been set up. If something expected but important happens within that duration, the data will not be collected.

Solved Example: 9946-01

The system widely used for data collection and acquisition is known as:

A. Scalable Control and Data Acquisition

B. Supervisory Control and Data Acquisition

C. Acquisition of Data and Analysis

D. Adaptive Data Acquisition

Correct Answer: B

Solved Example: 9946-02

PLC has become popular, because it performs _________ functions.

A. Data transfer

B. Timing and counting

C. Logical

D. Analog

Correct Answer: B

An Amplifier is an electronic device or circuit which is used to increase the magnitude of the signal applied to its input.

Gain of an Amplifier:

Voltage gain (A$_v$) = $\dfrac{\mathrm{Output\ voltage}}{\mathrm{Input\ voltage}}$
Current gain: (A$_i$) = $\dfrac{\mathrm{Output\ current}}{\mathrm{Input\ current}}$
Power gain = A$_v$ $\times$ A$_i$

An OPAMP (Operational Amplifier) is a low cost integrating circuit consisting of transistors, resistors and capacitors.

An OPAMP can be used as:

Simple Amplifiers
Summers: (Addition)
Comparators
Integrators
Differentiators
Analogue to Digital Converters

An OPAMP has two types:

Inverting (where the input signal is connected to the negative terminal of OPAMP)
Non-inverting (where the input signal is connected to the positive terminal of OPAMP).

Ong saluri, CC BY-SA 3.0, via Wikimedia Commons

Solved Example: 9939-01

In class B amplifier, the output current flows for:

A. Less than half input cycle

B. More than half input cycle

C. Half input cycle

D. Entire input cycle

Correct Answer: C

Solved Example: 9939-02

_______ is usually used in RF power amplifier and in amateur radio.

A. Primary amplifier

B. Secondary amplifier

C. Non-linear amplifier

D. Linear amplifier

Correct Answer: D

Solved Example: 9939-03

Push-Pull amplifier circuit is used as ______.

A. Power Amplifier

B. Audio Amplifier

C. RF Amplifier

D. Emitter follower

Correct Answer: A

Solved Example: 9939-04

The maximum theoretical efficiency of a Class A amplifier can be:

A. 50%

B. 75%

C. 25%

D. 100%

Correct Answer: A

Solved Example: 9938-01

The Communication between the components in a microcomputer takes place via the address and ____

A. I/O bus

B. Data bus

C. Address bus

D. Control lines

Correct Answer: B

ADC (Analog to Digital Converter) is an electronic device that converts a continuous analog input signal to discrete digital numbers. Importance:

All microcontrollers store information using digital logic.
Compress information to digital form for efficient storage.
Medium for storing digital data is more robust.
Digital data transfer is more efficient.
Digital data is easy to reproduce.
Provide a link between real-world signals and data storage.

Two stages of ADC:

Sampling

Reduction of a continuous signal to a discrete signal
Achieved through sampling and holding circuit
Must hold sampled value constant for digital conversion.

Quantizing and Encoding

Approximates a continuous range of values and replaces it with a binary number
Error is introduced between in put voltage and outpur binary representation.
Error depends upon the resolution of the ADC.

Types of ADC:

Flash ADC
Successive approximation ADC
Dual Slope ADC
Delta-Sigma ADC

Solved Example: 9945-01

A 10-bit ADC has a full-scale of 10.230 V, when the digital output is $(11 1111 1111)_2$ . The quantization error of the ADC in millivolt is _________.

A. 10 mV

B. 5 mV

C. 2.5 mV

D. 20 mV

Correct Answer: B

Solved Example: 9945-02

Find the resolution of a 10-bit AD converter for an input range of 10 V.

A. 97.7 mV

B. 9.77 mV

C. 0.977 mV

D. 977 mV

Correct Answer: B

Solved Example: 9945-03

A 6-bit ADC has a maximum precision supply voltage of 20 V. What are the voltage changes for each LSB present and voltage to be presented by (100110), respectively?

A. 0.317 V and 12.06 V

B. 3.17 V and 12.06 V

C. 0.317 V and 1.206 V

D. 3.17 V and 1.206 V

Correct Answer: A

A Digital to Analog Converter (DAC) takes a digital code as its input and produces an analog voltage or current as its output. The analog output is proportional to the digital input.

Digital to Analog conversion involves transforming a computer's binary output containing zero's and one's into an analog representation of the binary data.

Resolutionis the amount of variation in output voltage for every change of the Least Significant Bit (LSB) in the digital input. If the number of bits are 'n', then, number of output codes = 2$^n$, or number of steps in the output are = 2$^n$ - 1

Resolution = Step size = $\dfrac{V_{Ref}}{(2^n-1)}$

Most commonly used types of DAC:

Binary weighted resistor: Utilizes a summing OPAMP circuit, in which weighted resistors are used to distinguish each bit from the most significant to the least significant.
R-2R Ladder: Each bit corresponds to a switch, where if the bit is high, the switch is conntected to the inverting input of the OPAMP. If the bit is low, the corresponding switch is connected to the ground. it has the advantage of utilizing only two resistor values, but its conversion rate is slower.

Giacomo Alessandroni, CC BY-SA 4.0, via Wikimedia Commons

DAC Specifications:

Reference Voltage
Resolution
Speed
Settling time
Linearity

Solved Example: 9947-01

A 5 bit ladder has a digital input of 11010. Assuming that 0 corresponds to 0 V and 1 corresponds to +10 V, its output voltage will be:

A. + 6.5 V

B. - 6.5 V

C. - 8.125 V

D. + 8.125 V

Correct Answer: D

Solved Example: 9947-02

If the resolution of a digital-to-analog converter is approximately 0.4% of its full-scale range, then it is a/an _______. :

A. 16-bit converter

B. 10-bit converter

C. 8-bit converter

D. 12-bit converter

Correct Answer: C

Solved Example: 9947-03

A 6-bit ladder D/A converter has a maximum output of 10 V. The output for input 101001 is approximately:

A. 4.2

B. 6.5

C. 5.5

D. 9.2

Correct Answer: B