28 Electronic pressure gauges for areas subject to explosion hazards
(EX areas) Digital pressure gauges compliant with ATEX Keller AG für Druckmesstechnik has introduced no less than fi ve intrinsically safe electronic pressure gauges for use in areas subject to gas explosion risks. The type approvals are compliant with the ATEX Explosion Protection Directive regarding explosive gases. The electronic design of these devices is trimmed to minimise energy consumption, so it is also possible to replace the batteries inside areas with explosion risks.
The simplest version, model ECO 1 Ei, offers high resolution and reproducibility for both measuring ranges (-1…30 bar and 0…300 bar), together with accuracy (typical) of 0.5 %FS and an integrated min/max memory. The application range as per the ATEX directive is defi ned by identifi cation markings Ex ia IIC T5 or T6. Keller’s type LEO 1 Ei and LEO 2 Ei electronic pressure gauges feature microprocessor-assisted compensation to ensure an extremely narrow total error band (including temperature errors) of only <0.2 %FS over the entire range of operating temperatures from 0 ... 50 °C. The zero point can be selected freely within the four measuring ranges between -1…3 bar and 0…700 bar. An automatic switch-off function guarantees energy effi ciency. Both models feature sampling rates of 2 Hz and integrated min/ max memories. The special feature of the LEO 1 Ei is its additional memory for peak values. In peak mode (as it is known), even extremely short-lived peak values for system pressure are registered with a sampling rate of 5’000 Hz. These values are often critical for the lifetimes of hydraulic plants. For both these pressure gauges, the application range as per the ATEX directive is defi ned by identifi cation markings Ex ia IIC T5 or T6.
Another version of the ”Leo” type electronic pressure gauge, the LEO Record Ei, is equipped with an integrated data memory to record pressure and temperature progressions in the measuring medium. Outside of areas with explosion risks, the data can be transmitted via an RS485 interface to a PC, for evaluation with the Logger 4.X software (available free of charge). The LEO Record Ei can register pressures of up to 1’000 bar with a total error band of ±0.1 %FS. With a capacitive sensor, this type is also available for very low measuring ranges starting from 30 mbar (±0.2 %FS). The application range as per the ATEX directive is defi ned by identifi cation marking Ex ia IIC T4.
Featuring accuracy of up to 0.01% FS, the LEX 1 Ei electronic pressure gauge is a genuine reference and precision measuring instrument that has been specifi cally equipped with a 5-digit display for calibration and testing purposes. Pressure measurement ranges of between -1 bar and 1000 bar are available. The LEX 1 Ei also offers a min/max memory and a digital interface to generate PC protocols. The application range as per the ATEX directive is defi ned by identifi cation marking Ex ia IIC T6.
Features that are shared by all Keller digital pressure gauges include simple parameterisation and operation with only two buttons. The pressure display can be shown in various physical units that can be selected freely.
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I2C interface for areas at risk of explosion Intrinsically safe D Ei series
The KELLER D-line boasts a unique combination of highly robust industrial pressure transducers and the popular I2C interface. This successful series has undergone further development and an intrinsically safe version is now available too. The new D Ei series is approved for gas group II applications and can be used to measure absolute and relative pressures in zone 0.
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Various possible combinations for all manner of different applications
With its modular structure, the series permits numerous combinations, making it the ideal component for customisations using an I2C interface:
• OEM pressure transmitters for fi tting directly into a system’s existing drilled holes: 4 LD Ei...9 LD Ei
• OEM pressure transmitters with ultra-fl exible pressure connection for screwing into existing pressure systems: 20 D Ei • Pressure transmitters with a pressure connection and cable gland: 21 D Ei, 23 D Ei • Level sensor for measuring the contents of a tank up to a maximum fi ll level of 3 m: 26 D Ei
The OEM pressure transmitters are available in various sizes and form the basis for the other models with ultra-fl exible pressure connections or level sensors for measuring the contents of a tank up to 3 m.
The 21 D Ei and 23 D Ei models are pressure transmitters with metal casings and cable outlets. Each offers a different level of accuracy, dimensions, potential applications and numbers of variants. For example, the slightly cheaper 21 D Ei model has a simple cable gland to relieve strain and is suited to use in dry environments, while the 23 D Ei has a premium-quality cable gland boasting protection level IP 68, allowing it to be used underwater and making it ideally suited to use in fl ooded areas.
The I2C interface
Pressure transmitters with an I2C interface are normally only available in plastic or ceramic “consumer” housings, with only the compensatory parameters being stored in a memory. The intrinsically safe OEM transmitters from KELLER, however, have their own built-in DSP (digital signal processing) core, which balances and standardises the output values. The I2C (inter-integrated circuit) interface is designed to connect elements directly on a circuit board. The I2C is a bus system in that it connects multiple transmitters (slaves) to the same communication line. For instance, the intrinsically safe D-line combines a pressure interface for industrial use in tougher environments with an electrical interface for OEM applications.
Robust and fl exible in equal measure
The D Ei series consumes very little energy and is optimised for battery-powered applications. The total error band is just ± 0,7 %FS over a temperature range of 10…80 °C. The hermetically sealed sensor electronics and the compact stainless-steel housing (optional Hastelloy C-276) are extremely resistant to environmental factors.
With pressure ranges of 1 to 1000 bar and an internal two-chip solution that keeps the pressure sensor separate from the signal processing, the D Ei series is extremely fl exible.
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50337pr@reply-direct.com Piezoresistive OEM pressure transmitters with
Range of pressure transmitters for use in hazardous areas / Pressure transmitters for gas and dust atmospheres
Keller AG has now introduced a complete range of pressure transmitters for use in hazardous areas. These intrinsically safe transmitters offer measurement ranges of between 0,2 bar and 1000 bar, so they can be used for measurements of all types in areas subject to explosion hazards in Group II (Gas), and as per the relevant ATEX Directive. Individual types from the product range are also approved for Group I (Mining) respectively Group II (Dust).
Common features of all Y-line pressure transmitters include a very low temperature error, with correspondingly high measurement accuracy. Thanks to the integrated temperature sensor and an additional digital circuit, the range of envisaged operating temperatures can be divided into as many as 120 sections with a width of 1.5 Kelvin. During factory calibration, a mathematical model is used to calculate individual compensation values for TK zero point and TK amplifi cation for each of these sections; the values are then stored in the transmitter. During operation, these values are fed into the analog signal path according to the temperature, without reducing the 2 kHz signal processing dynamic. A relevant total error band for measurement purposes of ±0,8 %FS can therefore be attained over the typical temperature range of -10 °C to +80 °C. This includes all error sources, from linearity to range tolerance.
As an additional feature, Keller’s X-line pressure transmitters (Series 30) offer microcontroller- based electronic evaluation to ensure maximum accuracy. Each transmitter is gauged across the entire pressure and temperature range. This measurement data is used to calculate a mathematical model that enables correction of all reproducible errors. In this way, KELLER can guarantee high accuracy on the basis of an error bandwidth within the overall compensated pressure and temperature range. The user of industrial transmitters may specify a choice of compensated temperature range at time of purchase, depending upon the application; i.e., either -10…80 °C or 10…40 °C. Otherwise, level transmitters are provided with a compensated range of 0…50°C. The calculated pressure value can be read via the interface, and is simultaneously processed as an analog signal. At the digital output, the error band between 10...40 °C is a maximum of ±0,05% of the full range.
A varied selection of structural designs, electrical signals and mechanical connection formats guarantee that these intrinsically safe pressure transmitters can be used for an extensive range of applications.
The range includes models with internal seals as well as fully welded and fl ush front-sealed versions that measure pressure in absolute or barometric terms, or relative to ambient pressure. Various threads are available for the pressure connection, and different plugs and cables can be used for the electrical connection.
Users can also choose between typical industrial measurement signals with 3-wire technology (0…5V / 0 ... 10 V) or 2-wire technology (4…20 mA); on the high-precision pressure transmitters and submersible sensors in Series 30, an additional RS485 interface is available in addition to the analog output.
50338pr@reply-direct.com IET September / October 2019
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