final Flashcards
A to D for
analog input
D to A for
analog output
analog in
8 or 16
analog out
8
digital in
16
digital output
8
mixed module
4 analog in, 2 d in, 1 d out, 2 a out
AC to DC
bridge rectifier- 2 or 4 diodes
IED
intelligent electronic device
types of comm in scada
radio, ethernet, tcp/ip, cellular, serial
Dry Contact
power supplied from the terminal strip on the card.
Isolated
power supplied from an external power supply.
currently used power sources
dc battery, natural gas fuel cell, TEG: Thermoelectric Generator A device that converts heat into electricity, Solar Panels
UPS system
(Uninterruptible Power Supply) used in mission critical devices
surge protector
designed to protect electrical devices from voltage spikes
causes of leaks in a pipeline
Pipeline corrosion and wear,
Operation outside of design limits, Unintentional third party damage, Intentional damage
Failure to detect leaks can be broken into 4 loss categories
Loss of life and property
Loss of product and downtime to fix pipeline
Environmental impact
Fines and legal suits
methods used in detection of gas and/or oil leaks
Physical inspection of the area Add an odorant Line flow calculations Line pressure measurement Noise detection Pigging Computer based
PIG
Pipeline Inspection Gauge
pigging Purposes
Utility pigs – clean the pipeline of debris or seal the pipeline
Cleaning – remove solids or semi-solid deposits
Inspecting
Monitoring
Batch separation
Which pipelines cannot be pigged?
pipelines with butterfly valve because valve size is smaller than pipe size.
types of pigs
Steel Urethane Urethane and neoprene Spheres (foam, solid, inflatable) Gel
aga 7
Measurement of gas by axial-flow turbine meters
aga 3
measurement of gas by orifice metering
typical network configurations for wireless telemetry
Point-to-point
Point-to-multi-point
half-duplex
Advantages
Data gathering is simple
No collisions can occur on the network
Link failure is easily detected
Disadvantages
Interrupt type request from a slave requesting immediate action cannot be handled
Waiting time increases with the number of slaves
All communication between slaves have to pass through the master with added complexity
Interrupt system (Report by Exception)
Advantages
System reduces unnecessary transfer of data as in polled systems
Quick detection of urgent status information
Allows slave-to-slave communication
Disadvantages
Master may only detect a link failure after a period of time and only when system is polled
Operator action is needed to have the latest values
Collision of data may occur and may cause delay in the communication
Query and Response
The entity asking the questions (query) is the MTU and the entity providing the answers(response) is the RTU
Microwave
transmitting data over radio waves whose wavelengths are measured in small numbers of centimetre
UHF
Ultra high Frequency
VHF
Very High Frequency
scanning
process of sequentially reading the inputs, executing the program in memory, and updating the outputs
1 read
2 program execution
3 communication
4 output scan
SCAN TIME
time it takes to implement a scan cycle 1-200 ms
Selecting a PLC
Number of logical inputs and outputs. Memory Number of special I/O modules Scan Time Communications Software
Detailed Design Process
- Understand the process
- Hardware/software selection
- Develop ladder logic
- Determine scan times and memory requirements
Media Access Control
Generic term for a technique within a communication protocol that permits or denies access to the physical communication medium
HDLC
High-Level Data Link Control
SDLC
synchronous data link control
ADCCP
advanced data communication
control procedure
two most common modes of operation of HDLC
Unbalanced normal response mode (NRM)
Asynchronous balanced mode (ABM)
Causes of errors
- Attenuation
- Limited bandwidth
- Delay distortion
- Noise
Max Transfer Rate (bps)
2 B log M
where:
B is the bandwidth in hertz
M is the number of levels per signaling element.
Signal to Noise Ratio
10 log S/N dB
Distributed network protocol(DNP) layers
Datalink layer
Transport layer
Application layer
Internal noise
Thermal noise – due to electron movement through the circuit
• Imperfections in circuit design
• Stray signals from oscillators and amplifiers
• Intermodulation of stray low level RF produced by internal circuits
External noise
Natural origins – electrostatic interference, electrical storms
• Electromagnetic interference (EMI)
• Radio frequency interference (RFI)
• Crosstalk
Sources of interference and noise on cables
electrostatic (capacitive)
coupling, magnetic (inductive) coupling and resistive coupling.
Practical methods of reducing noise and interference on
cables
Shielding and twisting wires Cable spacing Tray spacing Earthing and grounding requirements Specific areas to focus on
Network topologies
Bus topology
Star topology
Ring topology
Media Access methods
Contention systems
Token passing
Ethernet
Contention systems
first-come-first-served
Network interconnection components
- Repeaters
- Bridges
- Routers
- Gateways
- Hubs
- Switches
Radio Modems
Work in 400-900 MHz band
modbus & profibus
analog
foundation field bus
discrete
hart
analog + discrete
