Data Acquisition and Interfacing (Section 4.5) Lecture 18

5-axis teaching robot – Chan Hian Full

System Set-up Interfacing card installed in CPU

PCL-812PG PCL-839

drivers Mechanical parts – transmission, stepper motors

PC-based Process Control Monitoring System - Chai Song Ling

System Set-up PC and Data Acquisition System

Data Acquisition system – sensor and signal conditioner

Introduction A data acquisition system consists of many components that are integrated to: Sense physical variables (use of transducers) Condition the electrical signal to make it readable by an A/D board Convert the signal into a digital format acceptable by a computer Process, analyze, store, and display the acquired data with the help of software

Data Acquisition System Block Diagram

Flow of information in DAQ 1.Input transducer – measure physical quantity 2.Output from transducer – conditioned i.e. amplify, filter, conversion 3.Conditioned analog signal – digitized using ADC 4.Digital information – acquired, process and record by computer 5.Modify physical signal, digital output converted to analog by DAC 6.Analog signals are conditioned 7.Output transducer interact with physical variables

Transducers Sense physical phenomena and translate it into electric signals. Examples: Temperature Pressure Light Force Displacement Level Electric signals ON/OFF switch

Signal Conditioning Electrical signals are conditioned so they can be used by an analog input board. Types of signal conditioner: –Amplification – Isolation –Filtering –Linearization

Analog to Digital (A/D) Converter Input signal Sampling rate Throughput Resolution Range Gain

Graph humidity inside rain shelter house versus time start from 12 am on March 22, 2009 until 12 am on March 23, 2009 Graph temperature inside rain shelter house versus time start from 12 am on March 22, 2009 until 12 am on March 23, 2009

A/D Converter: Input Signal Analog –Signal is continuous – Example: strain gage. Most transducers produce analog signals Digital –Signal is either ON or OFF – Example: light switch.

The data is acquired by an ADC using a process called sampling. Sampling a analog signal - taking a sample of the signal at discrete times. A/D Converter: Sampling

A/D Converter: Sampling Rate Determines how often conversions take place. The higher the sampling rate, the better. Analog Input 4 Samples/cycle 8 Samples/cycle 16 Samples/cycle

This rate at which the signal is sampled - sampling frequency. Sampling frequency - determines the quality of the analog signal that is converted. Higher sampling frequency achieves better conversion of the analog signals A signal of lower frequency is generated from such a process (this is called aliasing). Shannon theorem: Sampling rate is at least twice the highest frequency so that the sample gives the original form of the signal

A/D Converter: Sampling Rate Aliasing –Acquired signal gets distorted if sampling rate is too small.

Analog-to-Digital Conversion An ADC converts an analog voltage to a digital number. The digital number represents the input voltage in discrete steps with finite resolution. ADC resolution is determined by the number of bits that represent the digital number.

Analog to Digital Conversion for a 3-bit ADC

A/D Converter: Resolution

Resolution The resolution = is a function of number of bits ADC uses to represents digital data The higher the resolution, the higher voltage range is broken into, and therefore, the smaller the detectable voltage change. A 8 bit ADC gives 256 levels (2^8) compared to a 12 bit ADC that has 4096 levels (2^12). Hence, 12 bit ADC will be able to detect smaller increments of the input signals then a 8 bit ADC. LSB or least significant bit is defined as the minimum increment of the voltage that a ADC can convert E.g. - For full scale input signal of 10V, the LSB for a 3-bit ADC corresponds to 10/2^3=1.25V. However, for a 12 bit ADC, LSB = 10/2^12=10/4096=2.44mV.

Exercise 1 An ADC with word length of 10 bits. If the input analogue signal range is 10 V, what is the resolution of this ADC?

Answer The resolution:

LSB varies with the operating input voltage range of the ADC. If the full scale of the input signal is 10V than the LSB for a 3-bit ADC corresponds to 10/2^3=1.25V For a 12 bit ADC, LSB= 10/2^12 =10/4096 =2.44mV. Resolution of ADC, X axis is analog input

Bits The smallest unit in digital signal is the bit, a contraction of the more descriptive phase of binary digit. indicating 1 indicating 0 A bit is a single element in digital signal, having only two possible states: on (indicating 1) or off (indicating 0). Off0On1

Bytes Bits are organized into larger units called bytes, the basic unit of information in a computer system. 2 8 A basic byte contains 8 bits. The total amount of information it can convey is 2 8 (=256) possible combinations. Off0On1Off0Off0Off0Off0On1Off0 1 byte = 8 bit = 2 nibble 2-byte = 16 bit, 4-byte = 32bit 1 Kbyte = 1×2 10 byte = 1024 byte 1 Mbyte = 1×2 10 ×2 10 = 1,018,576byte 1GB = TB = 2 40

Analog-to-Digital Converter Theory N-bit ADC Analog Input N-bit Digital Output Analog Input Signal 0 Volt 1 Volt Digital Output Code. 5 V. 25 V. 75 Volt bit ADC Scale Step Size = = V

Example of Encoding (8-bit system)

Encoding (8-bit Bus, 0-5 V Input)

Exercise 2 Consider a thermocouple giving an output of 0.5 mV/ 0 C. What will be the word length required when its output passes through an ADC if temperatures from 0 0 to C are to be measured with resolution of C?

Answer The full scale output from sensor: 200  0.5= 100 mV With word length n, this voltage is divided into 100/2 n mV steps For a resolution of C, we must be able to detect a signal from sensor 0.5  0.5=0.25mV Thus, the word length: 0.25 = 100/2 n ;n = bit word length is required

Numbering system – binary, decimal, hexadecimal DecimalHexadecimalBinary A B C D E F1111

Numbering system – binary, decimal, hexadecimal = = Compare this to the conversion to hexadecimal, where each group of four digits can be considered independently, and converted directly: = 5 E B = 5EB52 16

Elementary Bus Structure Micro- processor Monitor ROM Optional User ROM System & User RAM User Input/Output Address Bus Data Bus Keyboard System Input/Output Display Addr bus – which addr to go Data bus – data from CPU to addr Control bus – command from CPU

plans.com/PDF/T4I_Reference_ Manual.pdf

A schematic diagram of Data Acquisition System

Example of Computer DAQ System Computer Timer Digital Control Circuit Trigger Interrupt Parallel/Series Input Port Parallel/Series Output Port A/D D/A Filter + - S/H Sensor Bridge Instrumentation Amplifier Input Strobe Display Control Output Strobe DAQ Board

Multiplexer Device where computer reads information from various channel one at a time Electronic switch Computer instruct MUX select particular channel and the data are read and processed E.G. electronic MUX – DG508ACJ – 8 i/p channel each ahs 3 bit address for selection

Sample and hold Take the snapshot of the sensor signal and hold the value Switch connect the capacitor and the capacitor hold the value until the new sample is acquired

Data Acquisition Software It can be the most critical factor in obtaining reliable, high performance operation. Transforms the PC and DAQ hardware into a complete DAQ, analysis, and display system. Different alternatives: –Programmable software. –Data acquisition software packages.

Programmable Software Involves the use of a programming language, such as: –C++, Visual C++ –BASIC, Visual Basic + Add-on tools (such as VisuaLab with VTX) –Fortran –C# Advantage: flexibility Disadvantages: complexity and steep learning curve

Data Acquisition Software Does not require programming. Enables developers to design the custom instrument best suited to their application. Examples: TestPoint, SnapMaster, LabView, DADISP, DASYLAB, etc.

48 Induction Motor Data Acquisition – Wong Kien Fatt To acquire input-output data for the model structure Figure 1: Actual photo of the whole experiment setup

LabVIEW 8.0 (Software) Analog input Block Diagram Figure 7: Analog input part of the block diagram

50 LabVIEW 8.0 (Software) Analog and Digital Output Block Diagram Figure 8: Analog and Digital output part of the block diagram

12/16/ LabVIEW 8.0 (Software) VI (Virtual Instrument) front panel

PREPARED BY: MOHD RAZIMAN BIN MUHAMMAD SUPERVISOR: DR. ROBIAH AHMAD

Figure 7: DIY anemometer Figure 8: Irradiance sensor Figure 6: Temperature and humidity sensor

PLACING SENSOR Figure 9: Sensor placing on rain shelter house

Figure 10: Block diagram for data collection Figure 11: Front panel for data collection COLLECTING DATA

Figure 33: Alarm on when humidity inside rain shelter exceed limit Figure 34: Alarm on when temperature inside rain shelter exceed limit Alarm on when humidity exceed 50% Alarm on when temperature exceed 31°C PROGRAM: ALARM ALARM

KPCI-3108

End of Lecture 18