By William Heath, Commercial Director, OMC
If your industrial fibre optic application is a new design, there are really three basic questions your procurement team must answer in order for us to supply the best fibre optic datalink. We need to know: 1. What the data rate is; 2. Over what physical distance you are sending the data; and 3. If there are any limitations on the drive current that you can supply to the emitter.
Given that information, as a fibre optic system manufacturer, we can then work out the optical budget, which will determine how powerful a transmitter you need, and how sensitive the receiver needs to be. Interestingly, one of the first questions that buyers expect to get asked is whether it is a polymer or glass fibre system. But for a new design, we prefer to specify the whole system link – transmitter, type of cable, and receiver – because then we can manufacture exactly what is required, also bearing in mind temperature and space constraints. It’s our job to deliver the lowest cost and most readily available means of achieving the system goals. The same goes for other parameters, such as fibre core size.
We also always look at system designlife requirements. If relatively short – say up to five years – we may be able to hit the LED with higher currents; but in general, high reliability applications in mass transit systems, power plants, or heavy industry will be specified for 30 or 40 years. If we’re producing a receiver, then whether the customer’s circuit requires an analogue or digital receiver output is also important information.
Where it gets interesting is when we receive purchasing requests for replacement components, be they for continued production of designs for which components have gone obsolete, or for legacy systems undergoing refurbishment.
There are many systems out there with fibre optic datalinks that were installed several decades ago. And it’s no surprise that the transmitters, receivers, and optical fibres that were used then are not available now. However, let’s say you’re having to renew one end of a datalink, and you’ve still got the original datasheet for the fibre and the transmitter/receiver. The temptation is to try to buy exactly the same part, or a part with identical specifications.
The problem with that approach is that often, older systems used universal components that were designed to be able to transmit over the longest feasible distance and down any type/
size of multimode fibre. However, if such universal parts have gone obsolete or can’t be found, the option is to make a custom part. In which case, let’s make a specific device that we can design to perform the exact task that is required. In that way, we can avoid the cost of special optics and semiconductors with an unnecessary performance range.
This was exactly the case we ran up against recently in a mass transit application for which a replacement transmitter device was needed, and the initial request was for a part with identical spec to the original datasheet. The old part was a universal device with a chip and micro-optic arrangement designed to focus the light into fibre cores from as small as 50 microns up to 1,000 microns. A like-for-like replacement transmitter was going to cost about £40 – and the semiconductor needed was on six months’ lead time! But when we were able to get answers to our basic questions, we found that the fibre being used had a 200-micron core; with that information in hand, we were able to produce a transmitter perfectly characterised for the task for around £10, using readily available components. If you consider that this application uses many tens of thousands of transmitters over many years, the long-term savings run into hundreds of thousands, if not millions of pounds.
However, it isn’t always straightforward to obtain this information. We find that there is often a reluctance to delve into the detailed technical specifics, particularly if this entails involving other departments beyond purchasing, such as engineering. But as the above example showed, the cost-savings that can be realised – or looked at another way, the wasted cost that can arise from not doing so – should essentially make this a vital part of the sourcing and procurement process.
Of course, new parts will demand re-qualification, but if the system has been installed for many years, the parts – if they are even still available – are likely to have changed anyway. It’s very rare for parts to exactly match an old datasheet, so re-qualification will almost always be necessary. And of course, another advantage of being able to specify readily available materials is that it’s then straightforward for us to produce a sample batch for evaluation in a relatively short timescale, which helps facilitate and speed-up the requalification process considerably.
This article originally appeared in the Jan/Feb issue of Procurement Pro.
