From the production of crisps to automotive assembly, the pressures on plant control are the same. If you focus on the pneumatics aspect, assuring optimal control comes down to ensuring that the sequence of operations function in exactly the order they should, and that if changes need to be made, you can make them as fast as possible with minimum disruption.
Chances are that in implementing a pneumatics solution, you’ve built it around PLC control, the mainstay in sequencing applications. But did you – or would you if you were solving a pneumatics application now – take the next logical step and implement fieldbus connectivity via your PLC master?
PLCs are often regarded as user-unfriendly when it comes to pneumatic system implementation. And there is worse news: a recent survey examining the market perception of fieldbus systems indicated that a lack of understanding was the reason that around 60% of the respondents were not currently using the technology. They were simply uncertain how to use it.
This dislike of PLC programming and confusion over fieldbus protocols – and fear of choosing the wrong protocol – has led Norgren to look at the problem and provide an answer it believes will increase the use of fieldbus linked, PLC controlled systems. Its solution is called Integrated PLC .
The traditional method of making a pneumatic system `intelligent` is, as far as possible, to group all the valves together and electronically control them by hard-wiring them under the control of a PLC, operating under ladder-logic software. If the system needs to be IP65 rated then the valves and the PLC are housed in a cabinet or enclosure so there are no exposed wires.
The Integrated PLC system was developed in response to requests from small machine builders and OEMs who wanted a simple mechanism to control pneumatics on their machines. By meeting IP65 the module is ideal for stand-alone machine applications.
The concept starts with the grouping of all the valves together on a manifold, or valve island. By themselves, valve islands are little more than dummies: the solenoids need energising to switch them on and off at a given time on the instruction of an electrical input, which takes them from being purely pneumatic to electro-pneumatic. This is where the PLC comes in.
Norgren claims to have taken a great step forward by integrating valve islands and PLCs together. At either end of the valve island an end plate is located housing the necessary wiring. The PLC is connected to the left hand side of the manifold via a `D’ plug making an integral unit. The PLC specified for the application is the Jetter Mikro, capable of driving up to 16 valves on the adjacent valve island and of receiving up to 16 inputs. It will also drive up to 62 additional valve islands. Paul Normyle, Norgren’s UK marketing manager comments: `We factored in the Jetter PLC because we found it to be the easiest on the market to use.
`Fundamentally, we wanted to ensure that the language was basic and simple to understand’.
The PC based software is bundled free with the unit and can be programmed with simple instructions on a PC or laptop. It is then taken to the unit and downloaded via lap-link. The software is intelligent enough to recognise straight forward commands such as `turn valve 1 on’, and `turn valve 2 off’. Additionally in the event of a failure there is no need for a specialist to come out and cure a software problem.
Flexibility is built into the system as it was felt that users would not commit to this system if future expansion was restricted. A key benefit of this system is that it can be used to control fieldbus.
As Normyle explains, ‘Our hardware is on Nugget valve islands. We can supply all the software you like. If your factory’s on Profibus-DP and you want Windows 95, we can supply it. Integrated PLC is the first step into systems control for machines.
`Our survey told us that 60% of our customers did not use fieldbus because they were uncertain how to use it. With Integrated PLC, we believe we’re taking away that uncertainty. Once you’ve become familiar with the technology then you can take the next step forward.’
The survey also highlighted the fact that users didn’t want to be tied to any one particular fieldbus protocol.
ALL OF THE OPTIONS
`All our valves talk to all protocols,’ says Normyle. `We particularly specify AS-Interface as it talks to all other fieldbus protocols via a gateway. You have the benefits of two wire systems without restrictions in any shape or form.’
The integrated system provides a low cost alternative to the traditional system of PLC and valve island in an enclosure with associated wiring. For IP65 rating, no cabinet is required for the integrated system as there is no external wiring. Installation time on the customer’s machine is cut by half as no hard-wiring is necessary between the solenoid valves and the PLC. When the unit leaves Norgren’s factory, it is fully assembled, tested and certified. On arrival at its destination the unit is unpacked from its box and bolted into position, and it’s ready to go.
The valve island pressure range is from zero to 10bar, and it is possible to regulate pressure and flow between valves. This, says Norgren makes it possible, for example, working on a 10bar pressure, for valve 1 to be operating off 4bar and valve 2 on 3bar.
Diagnostics are also built-in. By calling up a screen shot of the program, the software indicates the function being carried out when a fault occurred. Situated on top of the valve island are indicators which glow to indicate the faulty valve. There are also power saving coils fitted which extend the life of the coil and reduce consumption by half when they are operated.
Valve islands alone may not be new, but by integrating a PLC which is simple to program Norgren feels it has broken down the preconceived ideas about how difficult PLC controlled systems are to operate. In particular, Norgren reckons Integrated PLC will drive a more ready acceptance and use of fieldbus technology with pneumatic systems.