|
|
|
|
Operator Interfaces
Operator interfaces can be as simple as a stack light and panel lights to as complex as multi VGA displays on networked computers that send process data out around the world.
Understanding User RequirementsSystems & Business Analysts typically recognize at least three levels in systems: physical, logical, and conceptual. With respect to operator interfaces, let's discuss these three levels plus one more. Therefore our users, and interfaces, are: operator (physical), management (logical), process engineer (conceptual) and the fourth being maintenance. The operator is concerned with things they can touch. The manager is concerned with things they can measure, record, graph, and compare. The process engineer is responsible for making their process faster, better, and cheaper. The maintenance personnel are responsible for diagnosing foreign equipment like it was the only thing they ever worked on. We are offended at the term "operator interface". This is like saying that the other interfaces (i.e. other users) don't matter. We prefer the term "process interface" which includes an "operator interface", "manager interface", "process engineer interface", and "maintenance interface".
Operator InterfaceFor most operators the Operator Interface (OI) is a necessary evil and the operator wants a minimal amount of buttons and indicators to run the machine. Operators typically care about three things:
For operators with "incentive" contracts -- those operators will be interested in typical manager numbers that define how much their bonus is. Typically the minimum buttons you need for a process are: Start, Stop, E-Stop, and Reset. Start and Stop and E-stop are obvious. You might want to review our article "How do you stop?". We differentiate between Stop and E-Stop as stop means stop gracefully -- typically at the end of the next cycle. You want to be able to resume after a "stop" by simply pressing "start". E-stop is an emergency (hence the name E-stop) when you don't care about a restart, ruining parts, or anything but stopping as fast as possible. The Reset button is yet another safety feature that is often required for the operator to press the reset button before the start button. Pause means stop at any time and then recover -- which is different than stop and E-stop. This is usually not implemented with a button but with a light curtain or other "interrupt" that instantly pauses and then resumes. Not many customers request a "pause" option since the costs to design, implement, and test can easily double the amount of work to handle all the exceptions in a complex process. The minimum output for operators is typically a green light and a red light. The green light lets them know the machine is running correctly and they can go back to sleep. The red light lets them know the machine stopped because of some fault/error condition and they better start covering their butt. Neither light means that the machine stopped because an operator pressed the "stop" button and it is break time. We have been sarcastic about the operators :-))). Good operators have a lot more control over matters than most consultants and managers realize. Our experience has taught us that no matter how great of a job we do designing and implementing a system -- if the operators do not accept it -- the system will never work! We often like to use a yellow light to warn the operator about conditions that will soon lead to a fault/error stop. One example would be that a parts feeder is running low. This gives the operator enough time to get more raw parts into the system before the machine runs out of parts and has to stop. If the plant has an ERP / MRP system then the line supervisors will have additional operator interfaces to start and end lots, enter reject information, etc.
Manager InterfaceManagers love all kinds of numbers that can plugged into spreadsheets. The more numbers -- the happier they are! This includes:
There are fancy names for these numbers such as business / process ratios, Key Performance Indicators (KPI), or even "metrics". The bottom line is that they quantify, and measure, how well you are doing.
Maintenance InterfaceThe maintenance guys want to know what is wrong and how it happened. They want a lot of alarms, diagnostics, error trapping, and information about the alarms. They want to see detailed information on the I/O. Maintenance people are like detectives. Something bad happens and they have to look at the clues and figure out what went wrong. A great "process interface" will include for maintenance a running log file of exactly what happened and when (as specified in 21 CFR 11). This way the maintenance people can "reconstruct the bad scene" and review exactly what happened. Another concept is that cameras are so cheap now it is possible to set-up a camera and log the video to a computer hard drive. This way the maintenance people can go back and see exactly what happened.
Process Engineer InterfaceThe process engineer’s job is to make the process faster, better, and cheaper. The process engineer looks at both the operator interface, management interface, and maintenance interface but needs a lot more data that gives him an introspective look into the process. The process engineer needs to see mounds of data and analysis that you simply can not get by walking out and watching the process run. Some people refer to these as machine, or line, monitoring systems.
The process engineer will make the most progress by focusing on the slowest station, the station causing the most faults, etc. And the process engineer will have before and after data to compare after making changes. The process engineer needs to remember, IF you want the system to run faster, better, and cheaper THEN you need to display that those measurements to the operators and line supervisors. Let them see those performance indicators bright and clear all day long. If you show them those numbers then they will learn how to improve them a lot on their own.
Operator / Process Interface ImplementationTheory is great but sooner or later it has to become practical if it is going to be of any use. That is why we design (theorize) from the top-down and implement from the bottom-up. One last note on terminology before we continue. We differentiate operator interfaces from SCADA in that SCADA is doing much more than just an operator interface (for example collecting data from several sources, alarming, some control, etc.) SCADA will have an operator interface but an operator interface does not have all the features of SCADA. Depending on the application, what we are trying to accomplish and customer preferences we use a variety of techniques:
Our opinion is that every process should have some operator interface (or SCADA) on it. It is important to:
With everyone doing production reports -- why not let your production system automatically generate the reports for you?
We assume everyone understands regular mechanical buttons, switches, and indicator lights. Similar to what is found in your car to control the blinker, heating, cooling, turn signal, brake lights, warning lights, etc. Stack lights are like small traffic lights with green, yellow, and red lights. Options included horns, strobe lights, flashing lights, and other colored lights. Stack lights should be used on every application to quickly indicate to the operators the status of the machine. For example yellow lights indicate that one of the parts feeders is running low and will soon run out of parts. A red light means that the machine stopped for some reason. Which is why we suggest a more sophisticated operator interface in conjunction with the stack light. A more sophisticated operator interface, such as a text display or graphical display will tell the operator exactly why the machine stopped. Instead of the operator running around the process checking everything until they find the problem, the display will tell them the exact problem. Text displays typically work by someone storing text messages in the display. Each message has a number, for example 1 through 50. A message is then selected. The selection mechanism can be a simple register (or word) in a PLC. For example, suppose we store message 1 to be "Everything Great", message 2 to be "Parts Feeder Empty", message 3 to be "Motor Overload". So when the there are no problems you move a 1 into the register. When a motor overload occurs you move a three into the register. The corresponding message will be displayed. The next step up are devices such as Panelviews and Quick Panels that, on the high end, provide some graphics capabilities. These displays are usually very expensive (about $5,000 for a 9 or 10 inch color display) for their limited capabilities. For example they typically have a grid that you place controls on. To display a register or bit value you select the control and define what register or bit to read. It displays a value and allows you to type in some text for the name of the register you are reading. You can usually change the color of grids and backgrounds by associating a register number with a particular color. The next step up is the typical SCADA applications: Wonderware, Intellution, Factory Link, Think&Do. The hardware and software cost a lot more than the graphics displays but you can do a lot more with them. We have seen some applications where they have drawn beautiful three dimensional operator interfaces. They're stunning -- but rarely do customers want to pay for them. We typically use industrial graphics packages to minimize the cost. Another consideration is using Visual Basic or C#. You can get color, flat, panel mount, industrial computers starting at $2,000 that can run applications on the computer or load them off of a remote server (over Ethernet). So you can do a lot more for a lot less money. If you are afraid to use hard drives then load from the network server, use disk mirroring, or use solid state (memory based) disk drives. Recently we have seen a lot of interest in Personal Digital Assistants (PDAs) running CE.NET (or Pocket PC) operating system. We like the idea of sending status information to PDAs over wireless links. You can provide continuous updates of your manufacturing processes broadcast to the PDAs. However, please don't ever allow anyone to control the machine using a PDA or any other remote device! Sooner or later something very bad will happen. As far as programming with PDAs, we'll stick with the big screens on our laptops.
See Also
Operator Interface, HMI & MMI Links
We try to offer a fair and balanced opinion on every page of our website. We would appreciate more information from other operator interface users to express their opinions which we will then incorporate. If you have questions or comments please post them on our message board (see button in left hand column) so that others can read and benefit.
|
|
Click here to find out how High Tech Services can help you implement this technology. Copyright © 1984-2005 CompanyLongName HTS, Cary, Raleigh, RTP, North Carolina, NC. All Rights Reserved. All trademarks are the property of their owners. Prices and specifications subject to change without notice. |
