SIGNAL CONDITIONING FEATURE Keeping signals in tip top condition
Turck Banner explains why its expertise in the production of industrial sensors can help system designers when it comes to sensor choice and signal conditioning
I
n any data acquisition system, effective signal conditioning is vital to ensure the
optimisation of real-world signals, without which the accuracy of the measurement data is compromised. Depending on the type of input sensor, the signal conditioning needs vary extensively. Devices such as thermocouples produce very low-voltage signals, which require amplification and filtering, while strain gauges and accelerometers need excitation. Isolation of certain signals from high voltages is a common requirement, ensuring that the system not only delivers accurate data but is also safe. The key to a successful signal
conditioning system is to understand the circuitry required to ensure an accurate measurement whatever the channel mix. Selecting the correct hardware for signal conditioning is vital for an efficient, cost effective system. The choice of modular and integrated hardware options is vast and uses signal conditioning accessories in a variety of applications including amplification, attenuation and isolation. Where appropriate, system cost savings can be made via signal multiplexing. Turck Banner is able to offer appropriate
interface devices for separating, forming, processing, converting and conditioning analogue signals. Its product portfolio comprises analogue signal isolators, isolating transducers, temperature measuring amplifiers, potentiometer amplifiers, limit value and level monitors. Devices for Ex and non-Ex applications are available in IP20 housings for DIN rail as well as in compact IP67 housings for decentralised on-site remote control. In fact Turck Banner understands the
intricacies of signal conditioning and the required sensor inputs, ensuring complete system compatibility.
REQUIREMENTS A study of the development of interface technology reveals that customers increasingly have three key requirements: Safety, especially with regard to Ex separation and functional safety (SIL); the space requirement on the DIN rail; and performance, particularly in relation to speed and accuracy of the devices. Although existing interface devices can meet these requirements to a certain extent, the possibility of
The new IMX series has been comprehensively approved for Europe, North America, South America, China and Asia and is provided with UL, FM, ATEX, Nepsi, Kosha, Imetro and IEC-Ex certification
their further development is normally limited due to the original circuit design and construction. For many years, the company has offered a wide range of interface devices which have been continually adapted. However, it is only with a completely new electronic platform that a manufacturer can offer longevity in design, based on state-of- the-art technology, that can provide customers with investment security for the next decade. So, the company
has introduced a new generation of interface technology – the
compact IMX series. Development of this was carried out in complete compliance with the requirements of IEC 61508. Ex approvals can also present a
challenge, particularly when the same device is required for use in different countries. Unfortunately, Ex approval is not as uniformly harmonised worldwide as it is in Europe, where the ATEX directive is applicable in all countries. Different continents have different standards. The challenge for all device manufacturers is to cover the different requirements of all relevant Ex approvals combined, preferably in one device. To meet demands, the new devices have been comprehensively approved for Europe, North America, South America, China and Asia and are provided with UL, FM, ATEX, Nepsi, Kosha, Imetro and IEC-Ex certification. In the past, Turck’s MK series required
almost 3cm in width in order to process one temperature signal, while the current IM series requires 18mm for the same task. The new IMX series now only requires 6.25mm per temperature signal. Thanks to the narrow 12.5mm housing width, and up to four terminal banks per side, these devices achieve a channel density that is said to be unrivalled. Furthermore, the space requirement
on the DIN rail for the isolating switching amplifiers with a relay output (2-channel 4-wire resistance temperature sensors) has been reduced to half of that required by the IM series. Four separate removable terminal banks facilitate ease of connection as only actively used terminals need to be unplugged.
ACCURACY Turck has managed to increase both the accuracy and speed of the new series in spite of the narrow mounting width. This is highlighted particularly by the IMX12-AI EX analogue signal isolator. The new electronic design makes it considerably less sensitive to external factors such as temperature or voltage fluctuations. The effect of the interface device on the overall performance of a complete measuring circuit is thus reduced. In addition, ambient influences such as temperature, power supply fluctuations or changes in the connected load can have a considerable effect on the performance of devices. Turck recognises these errors and field conditions, and includes effects such as repeatability and hysteresis in the total error calculation. Thus the total performance is calculated from this together with the temperature coefficient. Quoted figures therefore reflect
performance in the field and not abstract laboratory conditions. It has been verified that the analogue signal isolators and temperature measuring amplifiers of the IMX series have the best overall performance in terms of accuracy of all 12.5 mm interface devices, Turck states. The IMX12-DI isolating switching
amplifier offers maximum processing speed. Input frequencies up to 15,000 Hz, can be processed, allowing precise measurement without the negative effect of signal conversion.
INDUSTRIES The process industry, particularly the chemical, pharmaceutical and oil and gas sectors, are traditionally the principal target markets for interface devices. The IMX12 series can be used in a 10 to 30 VDC range, opening up the possibility of use in new applications that are supplied from batteries, solar collectors or small wind turbines. Use in smaller mobile and autonomous installations makes the IMX devices of interest for manufacturers of small to medium-sized plants. Thanks to the international approvals available, manufacturers of centrifuges, decanters or biomass power stations can use the interface devices in plants for worldwide export.
Turck Banner T: 01268 578888
www.turckbanner.co.uk
INSTRUMENTATION | JULY/AUGUST 2016 27
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