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Jonas Neubert
WHAT IS A PLC?
AND HOW DO I TALK PYTHON TO IT ?
PYCON US 2019
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PROGRAMMABLE
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PROGRAMMABLE
LOGIC
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PROGRAMMABLE
LOGIC
CONTROLLER
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LC Inside
PLC Inside
PLC Inside
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PLC Inside
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PLC Inside
Photo by Annie Spratt on Unsplash
https://unsplash.com/photos/Iqwnr00mfQM
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Photo by Gonz DDL on Unsplash
https://unsplash.com/photos/a1Lm99Kkqtg
PLC Inside
PLC Inside
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Photo by Tyler Casey on Unsplash
https://unsplash.com/photos/ficbiwfOPSo
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Photo by Zhang JR on Unsplash
https://unsplash.com/photos/sCkqeWNGqMw
PLC Inside
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By Dusso Janladde at at Wikimedia Commons (CC-BY-SA 3.0)
https://commons.wikimedia.org/wiki/File:Nitro_coaster.jpg
PLC Inside
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PLC Inside
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Photo by Liesel at Wikimedia Commons (CC-BY-SA 3.0 Unported)
https://commons.wikimedia.org/wiki/File:Liesel_28-11-10_642_055-8_im_Bahnhof_Scharfenstein.JPG
PLC Inside
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Photo by Sebastian Terfloth at at Wikimedia Commons (CC-BY-SA 3.0 Unported)
https://commons.wikimedia.org/wiki/File:ICE_3_Oberhaider-Wald-Tunnel.jpg
PLC
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Official White House Photo by David Lienemann (public domain)
https://obamawhitehouse.archives.gov/sites/default/files/image/image_file/V020811DL-0076edit.jpg
PLC Inside
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Official White House Photo by David Lienemann (public domain)
https://commons.wikimedia.org/wiki/File:Cities_Sprinter_cab.jpg
PLC Inside
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Photo by Vladimir Kudinov on Unsplash
https://unsplash.com/photos/OwWIfjoVkbI
PLC Inside
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Photo by Daniel Åhs Karlsson at at Wikimedia Commons (CC-BY-SA 3.0)
https://commons.wikimedia.org/wiki/File:OTIS_GEN_2_Comfort_Roof_Taket_(Daniel_Åhs).jpg
PLC Inside
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PLC Inside
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Usually not a
PLC Inside
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Photo by Alex D’Alessio on Unsplash
https://unsplash.com/photos/sCkqeWNGqMw
PLC Inside
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PLC Inside
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Table of Contents
What is a PLC?
(and how does one program a PLC?)
How do I talk Python to it?
But what about RaspberryPi?
https: // jonasneubert.com / pycon2019
@jonemo
Q: What was THE acronym “PLC” for again?
A: Programmable Logic Controller
slides:
twitter:
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“Compact”
Fixed form factor
Photo of Siemens Logo by Stehfun at Wikimedia Commons (CC-BY-SA 3.0 Unported) https://commons.wikimedia.org/wiki/File:Siemens_Logo.jpg
Photo of Beckhoff CX by Beckhoff Automation GmbH at Wikimedia Commons (CC-BY-SA-3.0-DE) https://commons.wikimedia.org/wiki/File:Embedded-PC_Beckhoff_CX1020.jpg
This is what a PLC looks like*
“Modular”
Backplane with fixed
number of slots
“Expansible”
Infinitely*
stackable modules
* when it’s new
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This is what a PLC looks like*
* once it’s installed
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“CPU”
DI 4-20mA
DI 24V
AI 5V
DQ 24V
Motion Control
Serial Port
Power
Supply
PLC with 6 modules
Quick Intro to “Field Devices” Sensors Actuators
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The Input-Process-Output Cycle
Step 1:
Input Scan
Step 2:
Program Scan
Step 3:
Output Scan
Read process variables from Field
Instruments into PLC memory
Create “Process Image In” (PII)
Execute application program
(this is the Programmable Logic!)
Creates “Process Image Out (PIQ)”
STEP 2 is the
one we have
control over!
Read “Process Image Out” (PIQ)
Set output signals
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PLC Programming Demo
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Ladder Logic
| |
| DI1 Timer2Done DQ1 Red Light |
|------[ ]------|------[ ]----------------------(OUT)---------|
| | |
| DI2 | |
|------[ ]------| |
| | |
| Timer1Done | |
|------[/]------| |
| |
| OtherBoolVar Timer1 |
|------[ ]--------------------------------------(TMR)---------|
| |
| Timer1Done Timer2 |
|------[/]--------------------------------------(TMR)---------|
| |
Contacts
RUNGs
HOT
rail
Neutral
rail
COILS
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Ladder Logic
Photo of elevator logic by Tom Magliery on Flickr (CC-BY-NC-SA-2.0)
https://www.flickr.com/photos/mag3737/306386128
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Source: https://news.ycombinator.com/item?id=275587 (content edited for length)
Ladder Logic — Why?
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Ladder Logic
Still the most popular language for programming PLCs.
Common denominator across all PLC brands.
Part of curriculum for most Automation Engineering degrees.
A language optimized for debugging, not writing.
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Alternative Languages
- LD: Ladder diagram
- FBD: Function block diagram, graphical
- ST: Structured text, textual
- IL (deprecated):Instruction list, textual
- SFC: Sequential function chart , has elements to
organize programs for sequential and parallel control
processing, graphical.
- C/C++
- Matlab/Simulink
- Custom graphical wiring diagram tools
IEC-61131-3
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Demo 2
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Process Data
Process Parameters
Sensor Signals
Actuator Signals
The Two Control Loops of “IIoT”
Field Devices PLC Logic Python Code
“Inner Loop” “Outer Loop”
milliseconds per iteration
interfaces to the physical world
timing critical & safety critical logic
release process might be regulated
minutes to months per iteration
interfaces to databases and APIs
optimization & customization
regular software release cycle
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Vendor/Brand Specific Protocols
Protocol
Ethernet/IP
S7
ADS
DirectNet
DF1
PCOM
[unnamed?]
Vendor/Brand
Allen Bradley
Siemens S7 Series
Beckhoff
Koyo (Autom. Direct)
Allen Bradley
Unitronics
Fatek
Python libraries
pycomm
python-snap7
chwiede.pyads bfabio.pyads, adshli, pyads
clickplc
df1
pcom
fatek-fbs-lib
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
✓
RS-232/485
Ethernet
TCP/IP
CAN bus
see also: my spreadsheet of PLC brands and products and “List of PLC Manufacturers“ on Wikipedia
Best Case Scenario: You’re using one of these PLC BrAnds
Otherwise: go to next slide
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No Python support: CC-Link IE, Ethernet Powerlink, PROFINET, Ethernet/IP SERCOS III.
Utility libraries like rawsocketpy and dnet are handy for non-TCP/IP level networking.
“Open Standard” Protocols
Modbus TCP
Modbus ASCII/RTU
pymodbus, pyModbusTCP, cpppo
pymodbus, MinimalModbus
✓
✓ ✓
RS-232/485
Ethernet
TCP/IP
CAN bus
Protocol Python Packages
Ethernet/IP (TCP)
Profinet (TCP)
OPC-UA
pycomm, cpppo
GH: devkid/profinet
opcua, asyncua, opcua-client (GUI), opcua-webclient
✓
✓
✓
✓
✓
✓
EtherCAT pysoem
✓
✓
Profibus-DP
CANopen
SAE J1939
OPC Windows OLE
✓
✓
pyprofibus
canopen
j1939
OpenOPC
Many more with no Python support. Standard library sockets and ctypes are your friends!
Modbus is universal
40 years old this year!
see also: “List of Automation Protocols“ on Wikipedia
Ethernet based
“Fieldbus” standards
Many more with no Python support. Many require custom hardware or cables.
Other
TCP/IP based standards
“Office-to-Machine
networking”
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Example: pyads
import pyads
plc = pyads.Connection('10.23.19.3.1.1', pyads.PORT_SPS1)
plc.open()
plc.read_by_name('GLOBAL.RED_ON', pyads.PLCTYPE_BOOL) # → False
plc.write_by_name('GLOBAL.YELLOW_DURATION', 300, pyads.PLCTYPE_INT)
@plc.notification(pyads.PLCTYPE_BOOL)
def callback(handle, name, timestamp, value):
print(f"Notification: {name} has new value {value}")
plc.add_device_notification('GLOBAL.PEDESTRIAN_WAITING', callback)
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Example: pyads
import pyads
plc = pyads.Connection('10.23.19.3.1.1', pyads.PORT_SPS1)
plc.open()
plc.read_by_name('GLOBAL.RED_ON', pyads.PLCTYPE_BOOL) # → False
plc.write_by_name('GLOBAL.YELLOW_DURATION', 300, pyads.PLCTYPE_INT)
@plc.notification(pyads.PLCTYPE_BOOL)
def callback(handle, name, timestamp, value):
print(f"Notification: {name} has new value {value}")
plc.add_device_notification('GLOBAL.PEDESTRIAN_WAITING', callback)
Reference Variables by Name
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Example: pyads
import pyads
plc = pyads.Connection('10.23.19.3.1.1', pyads.PORT_SPS1)
plc.open()
plc.read_by_name('GLOBAL.RED_ON', pyads.PLCTYPE_BOOL) # → False
plc.write_by_name('GLOBAL.YELLOW_DURATION', 300, pyads.PLCTYPE_INT)
@plc.notification(pyads.PLCTYPE_BOOL)
def callback(handle, name, timestamp, value):
print(f"Notification: {name} has new value {value}")
plc.add_device_notification('GLOBAL.PEDESTRIAN_WAITING', callback)
Subscription to value
changes
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Example: opcua-client
Screenshot from project Readme: https://github.com/FreeOpcUa/opcua-client-gui/blob/c103b3f/README.md
the “UA” is important! Previous versions of
OPC are Microsoft-only legacy technology
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Example: opcua-client
Screenshot from project Readme: https://github.com/FreeOpcUa/opcua-client-gui/blob/c103b3f/README.md
Data and Methods are
discoverable in a tree of
nested objects
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Observations from reviewing 40ish Python packages
Lots of recent activity:
- 11 packages first published within the last 12 months
- 24 packages with new releases within the past 12 months
Many Python 3-only packages, few Python 2-only packages
Most activity in Europe*
* based on supported brands and package maintainer website information
Overlap with the much more active home automation community
e.g. homeassistant has support for two PLC brands built-in
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?
Raspberry Pi is a trademark of the Raspberry Pi Foundation
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Things you get from a PLC that you don’t get from a .
Hardware
Works in crazy environments
EM interference protection
ESD protected, isolated I/O
24VDC power, DIN rail mount
Expected life measured in decades
Supply chain guarantees
Safety certifications
Software (c.f. IEC-61131-3)
Realtime guarantees
PID control and Motion Control
Zero-downtime code changes
Industry-standard programming
languages
Support for common fieldbus
protocols
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But maybe the RaspberryPi is a PLC?
- CODESYS for RaspberryPi (codesys.com, €50)
Cross-platform IEC 61131-3 editor and runtime. The editor is
free, the RaspberryPi runtime is €50.
- OpenPLC (openplcproject.com, free)
A IEC-61131-3 editor (written in Python) and runtime for
various targets, including RaspberryPi
- PiLC (bues.ch/cms/automation/pilc.html)
Runs the awlsim PLC simulation software (an open source
Python package!) on RaspberryPi. awlsim implements a subset
of the languages and features of Siemens’ STEP 7.
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But maybe the RaspberryPi is a PLC?
Several products add a protected power supply, realtime clock,
isolated I/O pins, fieldbus protocol adapters, enclosures, etc.
- PiXtend (www.pixtend.de, €165+)
Extension board for RaspberryPi, communicates via SPI
Adds one or two Atmel controllers to manage I/O pins
Fixed set of digital and analog I/O, relays, CAN bus, RS-485
Programmable with CODESYS
- Andino (andino.systems, €135+)
- RevolutionPi (revolution.kunbus.com, €212+)
Custom PCB with RaspberryPi Compute Module
Raspbian OS with realtime patch
Expansion modules for I/O, many fieldbus protocols
Programmable with logi.CAD3
Revolution Pi product photo © Kunbus GmbH
PiXtend product photo © Qube GmbH, source: https://www.pixtend.de
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?
Arduino Community Logo, CC-SA-BY-NC 3.0, available at www.arduino.cc
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But maybe the Arduino is a PLC too?
- Controllino (www.controllino.biz, €135+)
Arduino-compatible custom board
Fixed set of digital and analog I/O, relays, RS-485
Modbus server for communications
Programmable with logi.CAD3 or Arduino IDE
- SoapBox Snap for Arduino (soapboxautomation.com, free)
A free ladder logic editor for Windows, and a corresponding
runtime for Arduino. Open source project, but sadly appears
to be unmaintained since 2016.
Controllino product photo © CONELCOM GmbH
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Hey Jonas, time is up and we all want to get
lunch.
What should I do next if I want to learn more
about this PLC stuff?
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Jonas’ PLC Shopping Guide
How much it’s going
to cost, approximately
If you want to do this:
Try out ladder logic
Try software the pros use
Program your like a PLC
Buy a cheap “real” PLC
Hack some real gear
Learn about the market leaders
Contribute to a Python project
Own a traffic signal
Then take a look at that:
OpenPLC, plcfiddle.com
List of free software in appendix
Codesys for , OpenPLC
Automation Direct, Siemens Logo!
Ebay1, industrial surplus sales
Allen Bradley (US), Siemens (Europe)
FreeOpcIUa, package list in appendix
County/state surplus auctions, Ebay
1 On Ebay, this is where you want to look: Business & Industrial → Automation, Motors & Drives → Control Systems & PLCs → PLC Processors
free
free
$70
$200
$500
—
—
$250
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What’s the URL for these slides again?
https://jonasneubert.com/pycon2019
Want to work with me?
https://www.zymergen.com/careers/
Watching this on Youtube?
The best ways to contact me are
Twitter (@jonemo) and email ([email protected])
Open Space
for questions, errata, and playing
with PLCs and traffic signals
Friday (today!) 3pm,
Room 21
#PyConOpenSpace
http://pycon.us/os
My last slide
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Free PLC programming software
Software packages that support multiple brands/platforms
Codesys — editor is free download, addons and device-specific runtimes are not free
Inforteam OpenPCS — same concept and pricing model as Codesys, but smaller market share
logi.CAD3 — base edition is free download
OpenPLC — open source
Vendor/brand specific software platforms
Beckhoff Twincat — trial license may be renewed indefinitely for personal use
ABB — free basic version
Vendors whose programming software is generally free: Automation Direct, Bedrock Automation, Phoenix
Contact, Unistream. Generally, smaller brands offer cheap or free software while market leaders use
software as a revenue stream. Avoid over-simplified “basic editions” that don’t resemble the full version or
don’t use IEC-61131-3 languages, for example Allen Bradley’s “Connected Components Workbench”.
Software with free trial versions that have reasonable limitations
Siemens TIA Portal — 21 day free trial, requires registration
Schneider Electric EcoStruxure Machine Expert — 42 day free trial
Panasonic — limits program complexity, no time limit
Keyence — only opens 50 times
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List of Python packages mentioned in this presentation
● pycomm
● python-snap7
● chwiede.pyads
● bfabio.pyads
● adshli
● pyads
● clickplc
● df1
● pcom
● fatek-fbs-lib
● pymodbus
● pyModbusTCP
● cpppo
● pymodbus
● MinimalModbus
● devkid/profinet (Github link, no PyPI project)
● opcua (part of the FreeOpcUa project)
● asyncua (part of the FreeOpcUa project)
● opcua-client (part of the FreeOpcUa project)
● opcua-webclient
● pysoem
● pyprofibus
● canopen
● j1939
● OpenOPC
● rawsocketpy
● Dnet
From the standard library:
● socket
● ctypes
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Forums and Online Communities
https://reddit.com/r/PLC/ — surprisingly friendly community, by Reddit standards
https://control.com
https://www.mrplc.com
Books
Sorry, I couldn’t find any books on the topic that seemed worth their price tag.
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Backup slides for Demo 1
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Backup slides for Demo 2
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Addon slides for (optional) Demo 2c
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from pymodbus.datastore import ModbusServerContext, ModbusSlaveContext, ModbusSparseDataBlock
from pymodbus.server.asynchronous import StartTcpServer
from datetime import datetime
def boolfmt(label: str, boolvar: bool):
return f"[ {label} ]" if boolvar else "[ ]"
class MyDataBlock(ModbusSparseDataBlock):
"""A custom data "storage" class that logs all incoming requests"""
def setValues(self, address, values):
super().setValues(address, values)
now = datetime.now().strftime("%H:%M:%S.%f")
g, y, r, h, f, w = [boolfmt(k, v) for k, v in zip("GYRHFW", values)]
print(f"{now} {g} {y} {r} {w} {f} {h}")
def main():
block = MyDataBlock([0]*100) # storing 100 words
store = ModbusSlaveContext(di=block, co=block, hr=block, ir=block)
context = ModbusServerContext(slaves=store)
StartTcpServer(context, address=('0.0.0.0', 502))
if __name__ == "__main__":
main()
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import socket
HOST = "192.168.1.9" # IP address of the PLC
PORT = 50505 # Arbitrary port I used in Ladder Logic
with socket.socket() as s:
s.connect((HOST, PORT))
s.sendall(b'REQ')
print(s.recv(1024)) # → ACK
s.sendall(b'DISCO')
print(s.recv(1024)) # → ACK
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back to slides