1. SCADA Communication and Architecture Principles
Mark Scantlebury, P. Eng., BASc.
President and CEO
11/21/2018

2. Overview SCADA System Basics Field Communications Modbus Protocol
Hazardous Locations
Field Architectures
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11/21/2018

3. SCADA Supervisory Control And Data Acquisition
General term for a system used to control and collect data from a set of remote devices.
Many choices for system architecture, types of devices, and communication protocols.
Concepts are simple, but systems can get complex.
Will discuss most popular systems used for oil and gas.
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11/21/2018

4. System Overview
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11/21/2018

5. Field Devices Many Different Types of Devices
RTU – Remote Terminal Unit
PLC – Programmable Logic Controller
Application Specific – i.e. Flow Computer
Responsible for Monitoring Local Sensors and Providing Control
Current Values Made Available
Some History Stored
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11/21/2018

6. Servers Communication Driver Retrieves Data From Remote Devices
Historian is a database that stores multiple historical values for a specific tag (value from a device).
HMI – Human Machine Interface is the set of screens made available to client devices.
Multiple items may be combined
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11/21/2018

7. Clients Many different types of client devices
Thick (installed) or thin (web) client interfaces
Can be connected to the network locally or remotely
Access always goes through the server
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11/21/2018

8. Field Communications
Many choices for communicating with RTUs/PLCs in the field
Allows the server to get information from each device
Most likely a polled architecture
Data can be sent from end devices
Modbus is still the most common
Typically cannot mix protocols unless over Ethernet
© Extreme Telematics Corp. 2013
11/21/2018

9. Understanding Communications
Protocol, Parity, Stop Bits, and Start Bits are all just definitions of what language is being spoken
Baud Rate is the speed of the message
Both the sender and receiver have to speak the same language at the same speed
Many physical ways to get the message there. Wire, Fiber, Radio, Satellite are some examples
The message is the same
© Extreme Telematics Corp. 2013
11/21/2018

10. Communication Layers Several interchangeable pieces.
All work together to communicate across devices
Application
Flow Calculator
Plunger Lift
Protocol
DNP3
Modbus
Physical
Radio Frequency
RS-485
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11. Modbus Protocol Master/Slave Polled Architecture
Broadcast (Everyone Hears Master)
Limited by time to complete polling cycle
Very easy to understand
Supported by large number of devices
Not the most efficient, but too much legacy to change overnight
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12. Postal System Same Layout Same Type of Device Sorting Center Mailbox
Local Post Office
Letters
Data
Register
Local Slave Device
Modbus Master
Different Layout
Different Type of Device
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13. Modbus Data Four Main types of Data
Coils – True or False. Can be read or written and usually executes some action. i.e. Open or Close Valve
Input Discretes – True or False. Read only. i.e. Battery Good
Input Registers – 16 bit number. Read only. i.e. Battery voltage
Holding Registers – 16 bit number. Read or write. i.e. Current Time
Combine multiple 16 bit registers to create a 32 bit number.
© Extreme Telematics Corp. 2013
11/21/2018

14. Modbus Format
Station Address – The address that this command is destined for
Command – Different codes to read or write different register types. Some codes indicate bulk data.
Register – The starting register to read/write.
Data – One to many bytes of data
Checksum – Ensures the data integrity.
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11/21/2018

15. Hazardous Locations Class I Div 1, Class 1 Div 2 Typical
Different Gas Groups
Different Temperature Codes
IEC is the more up to date, international standard
Referenced by latest CSA and UL standards
Uses Zones instead of Divisions
Div 1
Div 2
Previous
Zone 0
Zone 1
Zone 2
IEC
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11/21/2018

16. Hazardous Locations Zones Type of Rating Zone 0 – Gas is present
Zone 1 – Gas sometimes present normally
Zone 2 – Gas present under failure
Type of Rating
Explosion Proof – Explosion Contained
Intrinsically Safe – Will not cause gas to be ignited. Lower component temperatures and low capacitance.
Div 1
Div 2
Previous
Zone 0
Zone 1
Zone 2
IEC
© Extreme Telematics Corp. 2013
11/21/2018

17. Field Architectures
There are a number of different ways to connect devices in the field.
Typical Flow Monitor
Independent Plunger Control
Daisy Chain
Shared Communication
There is no right or wrong architecture.
Each has its advantages and disadvantages
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11/21/2018

18. Typical Flow Monitor Likely configuration of any existing network
Other Logic implemented in flow computer
Advantages
Less Hardware Costs
Simpler Hardware Configuration
Disadvantages
Limited space for programming
Programming may be basic or non-existent
Basic on site display if any
Access needs to be given to service companies
Costs to maintain software
Expensive Sensors/Interfaces
Solar
Radio
PLC/
RTU
Battery
Charger
Zone 2
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11/21/2018

19. Independent Plunger Control
Can Run standalone
Add Radio Panel to connect to SCADA
Advantages
Local Interface
Advanced Algorithms
No Development Costs
Service Companies Don’t Have Access to Flow Computer
Cost Effective Sensors
Disadvantages
Additional Hardware Costs
Solar
Solar
Plunger Controller
Radio
Barrier
Battery
Charger
Zone 2
Zone 0/1
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11/21/2018

20. Daisy Chain Combine Independent Plunger Control with existing SCADA
More Hardware Costs, but a lot of development and maintenance costs are offset
Some Programming of PLC/RTU Required
Solar
Solar
Plunger Controller
Radio
PLC/
RTU
Barrier
Battery
Charger
Zone 2
Zone 0/1
© Extreme Telematics Corp. 2013
11/21/2018

21. Shared Communication Shares radio instead of going through PLC/RTU
Simpler Implementation, but uses extra Modbus address.
Solar
Solar
Plunger Controller
Radio
PLC/
RTU
Barrier
Battery
Charger
Zone 2
Zone 0/1
© Extreme Telematics Corp. 2013
11/21/2018

22. Plunger SCADA Module Most Cost Effective and Flexible
Eliminates the need for a barrier
Uses Single Modbus Address
Uses Cost Effective Sensors
Eliminates battery, solar panel, and enclosure from plunger system
Radio
Battery
Plunger Control
Charger
Solar
Zone 2
PLC/
RTU
Zone 0/1
Radio
Battery
Charger
Solar
Zone 2
PLC/
RTU
Zone 0/1
© Extreme Telematics Corp. 2013
11/21/2018

23. Questions?
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11/21/2018 23