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Article | May 31, 1999
PC control grows up
Contract packager Beverage Capital becomes one of the first users of a 78-valve liquid filler controlled by a single PC. Benefits include ease of use, faster troubleshooting.
While PC-based controllers are no longer unusual on at least some types of packaging equipment they have yet to be adopted on a wide scale for many high-end packaging machines such as liquid fillers.One packager who recently made the leap to PC-based control on a 78-valve hot-fill liquid filler is Beverage Capital (Baltimore MD). In January the contract packager commissioned the filler from Fogg (Holland MI) to fill Snapple® ready-to-drink teas and juice drinks for Triarc Beverage Group White Plains NY. Beverage Capital also fills similar products for other customers on the Fogg machine as well as other fillers. The Fogg FPG filler which fills 16-oz glass bottles at about 725/min is run by a PowerStation(TM) PC control from CTC Parker Automation (Milford OH). That control runs CTC's MachineLogic(TM) control software and Interact human-machine interface (HMI) software.One reason many packagers have resisted PCs for control is the perception that troubleshooting such controls might be different compared to PLCs which are a known quantity when it comes to machine control. Beverage Capital was no exception. "We knew the filler was coming with a PC but we were a little anxious over the PC control" says Don Hamlett maintenance manager.However such anxiety soon proved unfounded according to Frank Hyatt maintenance supervisor. "What I found was that in a very short time I was able to learn enough about the PC to work with it" he says. Of course when most people think of PCs they think of the machine on their desk that crashes or locks up on occasion which is another reason most packagers resist PC control. After all it's virtually unheard of for a PLC to crash. However with nearly five months of operating experience under Beverage Capital's belt with the new filler Hyatt says the PC "has not crashed once" and has given no cause for worry over reliability issues. Part of the reliability is due to the fact that the PC-based control has no hard disk drive which can be prone to failure in tough industrial environments. Instead it stores all of its programming in a type of solid-state memory known as flash RAM that retains programs and data even after the power is turned off. Unlike a hard drive flash RAM contains no moving parts and hence isn't subject to mechanical failure.
The PC's reliability is also a function of the actual control software according to CTC. Called MachineLogic it does not run under Windows(TM) which was not designed for hard real-time machine control. Instead the PC control software runs under an operating system known as RTX DOS a version of which CTC says has been also used in many name-brand PLCs.
Hyatt says the PC control provides several benefits: It's quicker to troubleshoot a problem on the machine it's easier to modify the programming and it's easy to operate compared to the PLCs that Beverage Capital has used on its other packaging equipment.
"With only a little knowledge of the PC a person can track down any problem on the filler" says Hamlett. "So the benefit is ease of troubleshooting for routine problems without having to get in the program the drives or anything."
Beverage Capital had occasion to experience speedy troubleshooting when a sensor on the machine failed and had to be replaced. "Our mechanic was able to troubleshoot it within just a couple of minutes because the sensor indicator [on the touchscreen display] turned from green to red" says Hyatt. The entire process from troubleshooting to replacement took about five minutes. Also speeding replacement of sensors on this machine is the presence of a Profibus device-level network (see sidebar below).
Troubleshooting that same problem on a PLC-driven machine says Hyatt would be a bit more complicated. "We'd have to plug in a laptop computer and determine whether the sensor is bad by looking at the ladder logic" he says. That very act would rule out using a mechanic unskilled at reading ladder logic. "The last time I had to troubleshoot and replace a sensor on one of our other [PLC-controlled] fillers it took me and a helper probably two hours" says Hyatt.
Detailed list of faults
To further reduce troubleshooting time the HMI displays a detailed list of faults. "There's a readout for everything that goes wrong" says Hamlett. "All you have to do is read the description repair the problem reset and go." Troubleshooting times with the PC have typically been 20 minutes at most for some issues and as little as one minute for others says Hyatt.
Certainly such detailed troubleshooting reporting information could have been programmed into the PLCs that run Beverage Capital's other packaging equipment admits Hyatt. "But it would have been a real costly adventure" involving the purchase of color touchscreen displays and expensive software engineering time. The functionality that Beverage Capital has now came with the filler and PC control and didn't cost extra to engineer.
Nor is troubleshooting restricted to text messages at the bottom of the screen. A graphical representation of the filler shows for example when a specific safety door is ajar. "On our older machines you have to check all the safety doors [when the safety light is lit]" says Hyatt.
CTC says its PC control can be programmed with a mix of any of the five languages specified in the IEC-1131-3 standard a non-hardware-specific international standard for programming industrial controllers whether a PC or PLC. That standard more popular in Europe than in the U.S. is promulgated by an organization known as PLCopen (www.plcopen.org).
According to Dan Winebrenner the electrical engineer at Fogg that specified the PC most of the programming was done in an IEC-1131-3 version of ladder logic. Beverage Capital's Hyatt who is familiar with ladder logic programming on other PLCs says he was able to pick up enough of this version of the ladder logic programming in a couple of weeks to make modifications to the code. "I would think that most people who [have worked with PLCs] wouldn't have a hard time with it. The software has help menus so all you need to do is click help and it'll tell you what to do from there."
Like with a PLC programming changes can be made on a laptop computer which then plugs into the PC control to download the new program. Simple changes however can be done on the PC control itself simply by plugging in an external keyboard.
And because the same PC performs both the logic and the HMI functions it's faster and easier to add or modify the screens since only one control needs to be modified. By contrast making changes on an HMI linked to a PLC is a bit more involved since changes would need to be made to both the PLC programming and the HMI according to Hyatt.
Updates in the control programming of the PC can also be done remotely and installed by Beverage Capital without requiring an expensive service tech to come in and install the modified program. The contract packager tested this recently when it sought to add a bottle counter to the PC control. No new hardware was required. Instead the code was modified to read the output of an existing sensor as bottles passed by says Hyatt. Fogg's Winebrenner made the changes to the code sent the program to Beverage Capital via e-mail and Hyatt installed it and had it up and running within an hour he says.
The control is also very user-friendly for operators according to Hamlett. "Even if management walks by there's a couple of screens that are available for their use. If the regular operator is not there it's easy for someone" to use the control.
A final benefit of the control is that it has contributed to a smaller footprint for the machine while reducing the overall cost of the filler.
"Usually on most machines you pay an extra amount for electrics starters solenoids drives and Nema 4 electrical cabinets" says Hamlett. "You can pay big dollars for those big units that you attach to your wall." With the Fogg unit the main electrical panel which is also the operator panel measures 1.5'Dx1.5'Wx4'H. "I think we saved a huge amount of dollars as far as the building of the machine goes" says Hamlett.
The fact that control software doesn't run under a "standard" operating system like Windows doesn't bother Hyatt.
"All I know is my laptop [running Windows] crashed last week" says Hyatt. "This thing hasn't crashed once since we put it in. As far as the language or operating system goes whatever they're doing I think they're doing it right."
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