Within the process industry, two basic types of measuring resistors are used for electrical temperature measurement: wire-wound and film measuring resistors. Their different behaviour is reflected in the provisions of the European IEC 60751 (DIN EN 60751) standard, while the American ASTM E1137/E1137M treats the two types of resistors equally. This leads to confusion among users.
IEC 60751 leaves no room for interpretation. It lists the tolerance classes with their temperature ranges separately according to the nature of the measuring resistor. The basic values listed in the standard, the formulae for the permissible tolerance values and the test requirements apply to both types.
The detailed information has been present in the standard since 2008. The original EN 43760 standard from 1954 and its successors, from IEC 751 up to DIN EN 60751 from 1996, were developed on the basis of experience with wire-wound measuring resistors. Up to the revision of the standard, temperature ranges and class accuracies depended exclusively on the behaviour of wound platinum wires, which – embedded in ceramic or glass – change their resistance value as a function of the temperature.
The most important information, laid down as formulae and tables, was very clear. This included the basic values of -200 to 850°C, achieved using polynomials, and also two tolerance classes (A and B) and the associated temperature ranges -200 to 650°C (class A) and -200 to 850°C (class B).
Over the course of time, knowledge about the physical effects that occur in the platinum of the sensor at higher temperatures over longer periods of time has expanded. This has led to the necessity to adapt the standard to account for the drift behaviour of the measuring resistors so that it corresponds to the reality. A further reason for the revision was the development of film measuring resistors (also known as thin-film and flat measuring resistors or even chips for short) and their rapid market penetration.
This sensor type was not explicitly mentioned in the previous editions of IEC 60751: 2008 (DIN EN 60751: 2009). Users were therefore unsure whether the standard also applied to these new, cost-effective and exceptionally vibration-resistant measuring resistors. In particular, the specification of the temperature ranges suggested that film measuring resistors could be used at the same temperature limits and with the same accuracies as wire-wound measuring resistors. In reality, however, film measuring resistors behave differently to wire-wound measuring resistors, due to stretching and shrinkage effects as well as due to the diffusion of foreign atoms into the thin platinum layer. The result is a characteristic curve that leaves the standard range of permissible measuring deviations at low and high temperatures earlier than is the case with wire-wound measuring resistors. This behaviour physically arises as a result of the design and the materials used and must not be understood as a quality deficiency.
Readers wanting more information about updates to IEC 60751 and how the effects translate to the corresponding ASTM guidelines can download the full paper at http://instrumentation.co.za/+J1889
Inductive IO-Link sensors Turck Banner Southern Africa
Sensors & Transducers
Turck Banner is expanding its sensor range, with inductive measuring sensors with IO-Link and an analogue output for flush and non-flush mounting.
Read more...Value of PDS grows with data and sensing technology
Sensors & Transducers
Rapidly developing technology is constantly being harnessed by proximity detection systems (PDS) to deliver steadily improved functionality to customers. Booyco Electronics sees improved PDS solutions being developed, such as the combination of multiple different sensing technologies into a single fully integrated solution.
Read more...Pulp fiction or pulp precision? VEGA Controls SA
Sensors & Transducers
The density of fruit concentrate has a direct impact on the flavour, texture and overall quality of the final product. The VEGA Minitrac 31, VEGASOURCE 31, and the KV 31 mounting bracket present a failproof solution that effectively addresses the technical complexities associated with high temperature, viscosity and fouling.
Read more...Telco sensors in the pulp and paper industry Gail Norton Instrumentation
Sensors & Transducers
The pulp and paper industry poses a major problem for most photoelectric sensors. The high level of contamination in these dusty, dirty and grimy environments makes it impossible for most competing sensors to operate and sense reliably and efficiently.
Read more...Vibration monitoring with IO-Link ifm - South Africa
Sensors & Transducers
Machine vibrations are important indicators when it comes to assessing the current condition of a machine. fm’s new and smart IO-Link vibration sensor helps to implement a simple and scalable condition monitoring approach using only a single device.
Read more...Duct and plant room air quality (PRAQ) sensors Schneider Electric South Africa
Sensors & Transducers
Schneider Electric South Africa offers a comprehensive range of SpaceLogic duct and plant room air quality sensors. These cutting-edge sensors are designed to enhance building air quality and energy efficiency by combining multiple sensing capabilities into a single unit.
Read more...The sensory reaction of the BMS Schneider Electric South Africa
Sensors & Transducers
Today’s building management systems cannot function properly without sensors. Like our senses, they are an integral part of operations that run silently in the background, almost taken for granted.
Read more...Leaders in sensor technology Gail Norton Instrumentation
Sensors & Transducers
Photoelectric eyes have always needed perfect working conditions, but in the workplace there is no such thing. Steam, water, light and dirt interfere with most photoelectric eyes, but never with a Telco sensor.
Read more...A new era in top-notch measurement technology Senseca
Sensors & Transducers
In the ever-evolving world of sensor technology, a new name has emerged that brings a legacy of excellence, innovation and reliability - Senseca. This newly unified brand represents the merger of five industry-leading companies. All have a reputation for delivering top-tier sensor solutions, and have made significant contributions and set high standards in their respective industries.
Read more...Playing autoclave roulette VEGA Controls SA
Sensors & Transducers
Autoclaves ensure the sterility of medical and pharmaceutical products before reaching healthcare providers and their patients. To effectively manage these demanding conditions, VEGA provides reliable solutions, specifically the VEGAFLEX 81 and VEGABAR 83 sensors, which are designed to meet the stringent requirements of autoclave operations.