Seeing clearly

There have, in the past, been serious accidents where it has been difficult or impossible to clearly read what it said on the display of a sensor or instrument. It is sensible to mount a sensor in the place where it will produce meaningful information. Telemetry can usually be relied on deliver that information to the control system or instrument panel where it has to be made use of. There are, of course, limitations to this. The first is that the telemetry may not always be working. The second is that the instrument display may be a long way from the sensor and what it is monitoring. If a technician is doing maintenance, or investigating a fault, it may be essential that he or she can at once see what the sensor is indicating, especially if the measurand is pressure, and that pressure is either so low or so high that something undesirable is liable to happen quickly. There then comes the problem of reading the display in what may be quite an inaccessible place. It may be facing the wrong way, or is perhaps upside down, which, while still legible, is liable to lead to a misreading and any number of highly undesirable consequences. The Challenge Our challenge this month is to come up with a way of ensuring that a display on a pressure gauge can always be easily read. The solution could be optical, some kind of light pipe, or involve trained snakes that could go in and curl round and read it – if they could be relied on to deliver an accurate account of what they saw. On the other hand, the solution could be electronic, with the sensor delivering a message to the technician's PDA. All of these, however, involve some kind of added expense or complexity, when what is best, as always, is something simple, reliable and cheap. The solution is based on not one, but three pieces of lateral thinking. Once you see them, you may consider them to be obvious, but to our knowledge, most pieces of sensing equipment do not have these features, although we are sure that they will quickly become commonplace. An improvement has already been suggested, so we invite you to see if you can come up with something better. Solution The solution to our last month's challenge to find a way of preventing wires inside electrical and electronic modules from becoming trapped between enclosures and lids is to be found inside the Allen Bradley 800FC Pendant Station. These can have 3, 5, 7 or 9 holes in their enclosures, providing customers with up to 18 functions in a single pendant. Additionally there are mechanical interlock latches and an electrical interlock capability for one and two speed operators, which is achieved by wiring a normally closed contact block in line with each operator/function. This means that there can be quite a lot of power cables running up and down the pendant between the switch modules and the side walls. To prevent them overflowing the enclosure and getting trapped when the lid is put on, there are nylon fingers just inside the enclosure walls that bend inwards at their upper extremities. Threading the wires inside the fingers ensures that there is no way they can become trapped.