VUTRAX Application: Instrument

VUTRAX proves a safe bet for hazardous interface maker

It is a sobering thought that the safety of an entire oil rig or petrochemical plant could rely on the placement and tracking within a printed circuit board ...a reality faced every day by the designers at Measurement Technology Limited. The company makes process instrumentation modules, which limit the voltage and current entering hazardous areas. For its PCB design, it uses VUTRAX.

The instrumentation modules provide an electronic interface between safe and dangerous work areas, by limiting the power transmitted to a process area to a level which cannot cause an explosion in flammable atmospheres, a technology known as Intrinsic Safety. At the core of the module is its PCB, which is divided between 'safe' and 'hazardous' circuitry. The two must be totally isolated, with specific clearances between all components and tracking.

All component placement and tracking is performed manually and it requires an ECAD system that is both powerful and flexible. As James Cooke, Senior Mechanical Design Engineer, explains: "Three-quarters of the difficulty is getting the placement right. After that, the tracking soon follows. No other ECAD package I have seen has been capable of placing components as we require".

"The power of VUTRAX is that it allows designers to place and track as they want to. It does not force you along certain avenues. Clearly you have to understand the ramifications of what you are doing, but that freedom is essential at Measurement Technology. Other systems we've looked at are far more constrained; but with VUTRAX, if you keep your files legal and obey the design rules, you remain firmly in control."

Making intrinsically safe process instrumentation modules is a highly specialised business, with only a few UK manufacturers. Of these, Measurement Technology is the market leader worldwide. The company designs and manufactures in-house, exporting 75% of all production.

This Bedfordshire firm runs VUTRAX on 26 seats, all on networked personal computers. The fact that the system runs on PCs was an important consideration when Measurement Technology first introduced ECAD, back in 1988. The company was also impressed that you could buy only those modules that were needed; of the 26 seats only six are running the entire VUTRAX package and the configuration is very cost-effective.

Measurement Technology makes a number of smaller volume products, including multiplexers and displays, which incorporate digital work. In total though, the company works with analogue circuits 80% of the time. James Cooke feels that VUTRAX is particularly suited to this type of work.

"The circuit board layouts on our main product ranges tend to be 3 to 4 inches square. The analogue circuitry is physically small and very often highly accurate. It is complex, detailed work and VUTRAX is very good at it."

A 3 to 4 inch square board contains around 150 components usually, with an average of four pins. One thousandth of an inch here or there makes all the difference and for the products in question, cutting corners is unthinkable. Measurement Technology submits its boards to regulatory bodies in many countries to which it exports, so it always designs to the tightest of the different specifications.

Any modifications are entered into the schematic and worked into the circuit using the 'top-down modify' feature. Once a board design is complete and approved, the placement and tracking data is exported to the manufacturing facility. Work is occasionally sub-contracted out, but generally all boards are assembled on-site.

Routing is another function performed manually, except on limited digital work. Once again, the boards are too dense and complicated for any autorouting software. What Measurement Technology needs is raw power and while their VUTRAX system provides all the refinement needed for other functions, it is this power which determines the company's design success. The company's system works for designers, not the other way around.