MEASUREMENT + INSTRUMENTATION
as a sensor. With Memosens technology, they can be connected to the new generation of the Liquiline CM44 transmitters via plug and play and combined with all other Memosens sensors. Summary Without process analytics, there can be no process optimisation. As the ground-breaking Process Sensors roadmap from NAMUR confirms, users have long sought wider deployment of process analytics. However, this assumes easy commissioning, simple operation and maintenance that requires little effort. Before process spectrometers can evolve to genuine field instruments, know-how from different areas is required, from laboratory, automation and process control technologies. The biggest challenge lies in combining expertise from all these disciplines. If this happens, then a spectrometer could be like any other field instrument. The first promising developments are already on the market. □
that enables simple connectivity to a process control or cloud system and conversely permits remote access to the sensors and service data. The process spectrometer is evolving into an IIoT field instrument. The Memosens Wave CAS80E UV-VIS-based spectrometer offers reliable real-time measurement of relevant analysis parameters such as chemical and biological oxygen demand (COD/BOD), turbidity, nitrate and spectral absorption coefficient (SAC) in a single instrument. The CAS80E is optimised for beverage and surface water, wastewater, industrial wastewater and utilities applications and can be quickly adapted to specific applications with pre-installed analysis models. The Memosens Wave CKI50 process spectrometer detects colours by using spectroscopy in the visible range of the electromagnetic spectrum. It outputs the colour in a three-dimensional colour space model in the form of CIE L*a*b* values. That means colours, colour variations or the accuracy of the expected colour can be determined. The mathematical analysis models required to analyse the spectroscopic results are stored in the instrument. Both spectrometers are as compact and easy to install
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MEASUREMENT + INSTRUMENTATION : PRODUCTS + SERVICES
Reed level sensor: a flexible measuring range
A float-based level sensor with a reed chain is a widely used and comparatively economical solution for contin- uous level measurement in vessels. Users can define its measuring range flexibly within a given scope. When considered for application, there are a number of factors to be taken into account. With a reed-chain level sensor, the guide tube con- tains a defined number of reed contacts, depending on the measuring range. These are combined to form a measuring chain. The contacts react to the magnetic field of the float, which moves within the guide tube in line with the liquid level. Accuracy depends on distance The accuracy of this energy-free level monitoring in- strument depends, in turn, on the distance between the individual contacts: the smaller it is, the more accurate the measurement. Each level sensor in WIKA’s RLT se- ries, for example, enables measuring ranges with con- tact distances between 3 and 24 mm. However, a reed chain cannot be stretched along the entire length of the guide tube. This is because there are ‘dead bands’ at both ends of the tube, that is, sections the float does not detect due to design constraints (as shown at right). Defining the measuring range The measuring range of a level sensor therefore lies be- tween the two dead bands specified in the data sheet. Within this range, it can be freely defined. However, it is not necessary to use the maximum possible measuring
range in all applications. The exact adaptation of the number of con- tacts to the measuring task also has an economic advantage – as the reed chain is one of the most expen- sive components in a level sensor.
Dry run monitoring For dry run monitoring in an oil tank of a compressor, for example, only the lower part of the guide tube is needed for the measurement. In this case, the upper measuring point of the application (100% mark) is set correspondingly low. It marks the distance to the sealing face of the process connection. The measuring range is thus defined by the follow- ing equation: Measuring range length M = guide tube length L – dead band T – 100% mark X Consequently, the measuring range for detecting a maximum level is determined starting from the sealing face. In this case, the guide tube can be adapted to the length of the measuring range. For more information contact WIKA Instruments. Tel: +27 (0)11 621 0000 Email: sales.za@wika.com, visit: www.wika.co.za
The graphic shows how the maximum possible measuring range (M) with an air-handling series level sensor is defined: Guide tube length (L) minus dead band (T) and 100% mark (X).
MARCH 2022 Electricity + Control
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