By Brian Tinham
Temperature measurement and control hardly the fastest changing of technologies; well certainly not on measurement. Control is a little more lively, but it’s pretty standard stuff, isn’t it?
Well, as is so often the case, the answer is yes and no! In terms of the hardware itself there are incremental developments. Among the latest to be drawn to my attention include a 1/32 DIN temperature controller from West Instruments (the 2300 with universal inputs, multi-colour LEDs, comms and auto set-up) claimed to be smaller than a mouse and much easier to control!’
Then there’s an interesting new temperature transmitter from Rochester Instrument Systems. Its latest SC4400 two wire programmable head- and field-mounted device now includes diagnostic software, enabling fault analysis (sensor and transmitter) and calibration without invading the field wiring good for commissioning and maintenance.
And what about all the non-contact (infrared) two-wire, loop-powered transmitters, from the likes of Land Infrared, Ircon and Raytek? Land has just brought out a signal processor (Landmark Basic) for its System 4 range, said to ease the path of integration with your control system, whatever it is.
So much for the hardware; what about engineering practice? This has always been the bug bear with temperature installations. It’s true with all measurements get the details wrong and no matter how sophisticated your system, it will deliver rubbish! It seems extraordinary that with so few sensor types (primarily thermocouples, RTDs, thermistors, infrared units, integrated circuit (IC) sensors and fibre optic systems like York Sensors’ distributed time domain reflectometry system) there should be so much to deal with. Yet this remains the case.
So it’s excellent news that two new temperature measurement reference works are now available. Even better news they’re free! One is by TC and the other, Calex. TC’s replaces its earlier wall-hanging publication and is massively expanded with some 37,000 words and 73 A3 pages covering every aspect of thermocouple and resistance thermometry. Calex’s book is a conventional A4 publication, and the ninth edition of its work, with 150 pages primarily on infrared measurement.
TC says it intends its tome to be used as a day-to-day technical reference and guide as well as for training. It’s entirely independent and presented in four parts: concepts, theory and standards; sensors, equipment and practice; practical points; and future sensors.
Central to the compendium are sections on the advantages and disadvantages of the sensor types (sensitivity, accuracy, stability, response times, etc) and the suitability of the various application methods. Thermocouple styles, insulating materials, operating characteristics, designs of RTDs and assemblies and digital and smart transmitters are also explained.
You also get full details of thermocouple codes, conductor combinations, characteristics and national and international standards for outputs and extension and compensating cable colours. Reference tables cover all the types along with power series expansions, etc.
There’s also a glossary of thermometry terms and a further reading reference. All this, combined with explanatory diagrams, tables, schematics and product data, makes it probably the most useful offering to date. It certainly ought to be open on just about every practising engineer’s wall.
Calex’s work, on the other hand, majors on infra red thermometry, with nine pages of useful data on the theory, developments and practicalities of using IR devices. However, the bulk of its information is product- and industry application-orientated although there is a lot to learn from these, particularly the latter. Industries covered include food and drink, glass, metals converting, paper, petrochemicals, plastics, steel and textiles.
Subsequent sections on thermometry and associated instruments/accessories are relatively short on information and long on product data but it’s a useful publication for all that.