Schneider PLCs Micro and
Premium. Arduino.
MSc dissertation
proposal 2014/2015
Introduction:
Building real world reliable and robust systems
usually means using Programmable Logic Controllers (PLCs).
PLCs are modular digital computers that allow using a
large variety, and number, of electrical input and/or output interfaces. The
mechanical, hardware and software designs are made robust in order to handle
continuous operation in environments overwhelmed with electromagnetic and
mechanical (e.g. vibration) noise. Without noticing, PLCs
are almost everywhere, from the industrial assembly lines, to the elevators,
power grid control, etc (see [PLC_intro]).
Monitoring PLCs is usually
provided by proprietary (closed) software. The manufacturers of the PLCs generally provide the monitoring software but do not
open their interfaces. When one needs to develop hardware peripherals, or
hardware that interacts with PLCs, effective (fast)
monitoring is frequently hard to obtain with the provided software
monitoring tools.
Objectives:
The main objective of this work is the design of an Arduino based hardware
interface that allows fast monitoring of the physical interface of a PLC.
Detailed
description:
Major automation companies offer modular digital
computers that allow using a large variety, and number, of electrical input
and/or output interfaces, the so called Programmable Logic Controllers (PLC -
term invented by Allen Bradley [PLC_intro]). Together
with the hardware, the automation companies also offer, or sell, monitoring
software. The software interfaces are however usually closed. Developing fast
monitors of the physical inputs and outputs of a PLC is normally challenging or
even impossible with the tools provided by default by the automation companies.
In this work is proposed the construction of a
hardware "sniffer" for the digital (physical) interface of PLCs, namely the PLCs available
in the IST/MEEC graduation courses, i.e. the Schneider Premium TSX57 [Schneider_Premium]. The choice of constructing a hardware
interface brings the advantage that the operating frequency can be much higher
than the frequency that monitoring software can provide. In addition, being an
external hardware interface, one has the guarantee that monitoring does not increase
the memory/time complexity of the PLC software.
The proposed hardware to implement the
"sniffer" is the Arduino [Arduino-www] combined with a logging shield. In particular one
has to pay attention to the voltage levels, 5V in the Arduino
vs 24V in the PLC. While reducing can be done simply
by a voltage divider, augmenting from 5V to 24V implies using, for instance, a
comparator and a DC-DC converter for power supply.
Another aspect is the number of monitored binary
channels. The most common Arduino, the "Uno",
has just 14 digital inputs / outputs, which is much lesser than the common 16 inputs
+16 outputs found in the PLCs. Strategies for augmenting
the number of monitored channels are also supposed to be discussed.
The
work is therefore organized in the following main steps:
-
Developing one input and output, pass-through, bit hardware interface between
the Arduino and the PLC
-
Logging along time the binary signals passing through the bit interface
-
Replacing external power to the interface by the USB powering of the Arduino
-
Augmenting the number of IO bits handled by the interface
References:
[PLC_intro] "What is a
PLC?", in Machine Information Systems website, http://www.machine-information-systems.com/PLC.html
[Schneider_Premium]
"Schneider PAC, PLC & other
Controllers" http://www2.schneider-electric.com/corporate/en/products-services/products-services-intermediate.page?f=NNM1:PAC%2C+PLC+%26+other+Controllers&p_function_id=2
[Arduino-www] "Arduino open-source electronics prototyping platform",
http://www.arduino.cc/
Requirements
(grades, required courses, etc):
-
Expected
results:
At the end of the work, the students will have
enriched their experience in creating system based on a PLC using
off-the-shelve components. In particular are expected to develop and assess:
- The hardware integration of the various components
-
Software to interface and monitor the system
Place
for conducting the work-proposal:
ISR / IST
Quotation:
"In summary...you don't always get the luxury to
pick your term project, but if you can, find a problem you want to solve for
yourself in your own life. Design a novel solution for it with a PIC or other
microprocessor. Wire it up and program it. Understand the hardware and software
well so that you can present it well. Have a fun time doing it. If you find
that you lose track of time while you are working on the program and find it
hard to put it down even at midnight, you've got exactly the right idea! Best
wishes!"
More MSc
dissertation proposals on Computer and Robot Vision in:
http://omni.isr.ist.utl.pt/~jag