The majority of work performed by Chinook is on PLC based control systems and their integration with other processes. Programmable Logic Controllers are basically computers with built in wiring interfaces for the control of equipment and monitoring of sensors for system status. When required by the process or client Chinook provides PC based control systems. Mainly the only difference is that the processor is not integrated into the wiring hardware. The PC processor is used to perform all control algorithms. The following information applicable to both types of systems
PLC systems range from small machines with one function to large distributed systems that encompass an entire facility or multiple locations. The engineers at Chinook have experience with the entire spectrum. One PLC can have hundreds of I/O (inputs & outputs) points spread over a large area. In addition and any number of PLC systems can be linked to form one big coordinated process with self sustained nodes.
There have been many advancements in PLC in recent years. 15 years ago the minimum price for using the most basic PLC started around $2,500. Now micro PLCs allow small tasks with minimal I/O to be performed for $100 in hardware. On the other end, many types of PLCs now contain the ability for Motion Control - extremely precise control of multiple axis of motion.
There are many considerations that go into the design of a PLC system. Chinook prides itself in providing systems that are tailor made for each clients specific needs. We will rarely bid a job solely from a specification. An interview is required to determine the parameters required form each client.
Safety functions, fault monitoring, failure prevention, maintenance design and the
operator interface are examples of features that are glanced over or ignored
completely by clients. All affect the cost of ownership for the control system.
Future possibilities for expansion & integration are often difficult for clients to anticipate. Once a system is in place the owners gain a better understanding of the possibilities from automation and their needs evolve with that knowledge. This creates increased future requirements that the PLC system may or may not be able to accommodate. Many times the most expensive part of a control system is its lack of flexibility resulting in future replacement instead of upgrading.
While the advanced concepts above require a personal explanation from the Chinook staff to be determined, there are basic design considerations you may begin to review while developing the criteria for your system. An overview of these is shown later on this page.
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DESIGN CONSIDERATIONS
I/O Count
The major breakdown between categories of PLCs the amount of I/O. While an exact number is not required you should have a general idea of the amount, 5-15, 50-75, 300-500.
Of course this (and all following considerations) is not required
and can be completely determined by Chinook.
I/O Type
There are many types of I/O with even more configurations. The main consideration is the amount of discrete (on / off) and analog (variable) points. Discrete I/O is used for True/False status, for example a button, limit switch or run signal to a motor. Analog points provide a variable input or control. A temperature reading is an example of an analog input producing a value in a given range. If temperature is involved in a process but only a threshold is required, a temp switch can provide a discrete input to indicate above or below that point.
I/O Location
The relative location of all I/O points is another major factor in the type of PLC platform that is used. A basic system consists of points that can all be directly wired to one location or PLC rack. When devices are spread over a larger area a distributed I/O system is used. These platforms provide multiple wiring hubs that are connected by a communications highway. The prevalence of Ethernet I/O now allows points located anywhere on your LAN to act as if they are in the same place.
MMI Type and Location
The MMI (Man-Machine Interface) configuration used on a system impacts the ease of use, flexibility, serviceability, down time and information reporting of a system. We have found that for larger systems a distributed MMI configuration is the most efficient. The MMI ranges a simple ON light or control panel to advanced computer graphics with automated performance reporting, data logging and fault history.
PDAs, cell phones and pagers can be used as part of an integrated solution.
Chinook can make system Information and/or Control
available from any authorized PC on your LAN
Integration with other Systems
If the control system is required to transfer information to or from another machine or process, the method must be determined prior to design. If I/O signals are used the only thing required is to make sure enough are provided. If processor to processor communications is required the PLC system must have the required highway protocol.
Performance and Reliability
Determine how critical the machine or process is to your business. If the operational status has little impact on your company a basic control system is appropriate. If down time will stop production and send workers home, the cost alone justifies, if not demands, that the machine should have advanced features to greatly reduce failures and the down time resulting from them.
Environment
Physical environment can have a large influence on the design of a PLC system.
- Combustible Environments - Paint booth etc.: depending on the level the system must be wired intrinsically safe or explosion proof.
- High EM Interference: requires special precautions for wiring runs and protection of analog I/O.
- Air quality: The type of control panel cooling and secondary enclosures is affected.
- Corrosive Environments: Panels must be corrosion resistant along with all conduit and other wiring pathways.