Sensors & Transducers e-Digest (S&TD)
No. 8, August 2001
Table of Contents
By Katsan I.I. and Lupina B.I.
NIUU, Kiev Polytechnical Institute, Electronics Dpt.,
Polytechnic str., 16, Lab. 07b
Kiev, 03056, UA
Tel./fax: + 380 44 241 87 26
New Multi-Element Capacitive Sensor & High Bandwidth Preamp Form Basis Of Data Fusion System For Real Time Measurement Of Individual Blade Tip Clearance, Blade Vibration, Crack Detection And System Vibration In Aircraft Engines And Industrial Machinery
Mike Drumm & Dr. Wayne C. Haase, ExSell Instruments, Acton, MA
This paper describes the development of a high bandwidth, capacitive sensing system to monitor blade tip clearance, system vibration, blade time-of-arrival, blade vibration and detection of low cycle fatigue cracking on aircraft engines and industrial machinery. All measurements are fused into a single sensor and single channel of electronics. The paper describes the development of the multi-element capacitive sensor and high bandwidth preamplifier, presents results from tests conducted in a spin pit, and compares their time-of-arrival performance to the current Non-Intrusive Strain Measurement System being developed by the Propulsion Instrumentation Working Group. The system measures the clearance between the tip of each blade on a rotating disk and a thin multi-element capacitive sensor mounted close to the rotating part. The sensor is coupled to a very high bandwidth and high signal-to-noise preamplifier that allows detection of individual blades in real-time and the use of narrow striped capacitive sensors for increased resolution. The device can be used as the heart of a rotor health monitoring system for detection of High Cycle Fatigue blade vibration, Low Cycle Fatigue disk cracking, active tip clearance control input, blade damage from foreign objects, and monitoring of system vibration and speed.
964 Autumn Oak Circle
Concord, CA 94521
Tin Technology Step Forward for Pressure Sensors
New Article from Engineeringtalk.com
Sensor-Technik UK is launching a new series of pressure sensors featuring what is claimed to be a breakthrough in technology. The company's TiN (titanium nitride) thin film coating sensors are particularly compact, and the precision and long-term stability specifications are similarly impressive. The patented design is the result of two years' development at German manufacturer KMW, following research by Prof. Mueller at Hamburg Technical University. The diaphragm, in the form of a capsule, is welded onto the mechanical port without the use of any sealing materials, giving a totally sealed (water/air-tight) connection. By including integrated temperature compensation on the diaphragm, the need for external electronics is brought to a minimum (simplified). This also allows the temperature compensation to take much faster effect as it is mounted with the strain gauges. The design offers advantages over piezoresistive sensors, where the capsule diameter is relatively bigger, and over ceramic diaphragms, which are slightly higher in cost and need other sealing materials, which can affect the stability significantly. There are other thin-film pressure capsules on the market, but with nickel-chrome, for example, if the pressure sensors are subjected to high temperatures, the nickel-chrome-film is relatively quickly pushed to its limits. Compensating for this brings problems, notably high cost and loss of long-term stability. TiN-thin-film can go direct onto the media, and the long-term stability is high as the film is manufactured directly on to the sensor material. TiN thin-film technology has already been tested for more than 1000million cycles on large diesel/gas engines. The gas temperature during startup is over 1000C. The temperature effect on the TiN-thin-film pressure capsule is under 1% per 100C; the resistance is controlled, so that the temperature influence is quickly compensated. Although earlier types of thin-film pressure measurement technology are now used widely, the foil strain gauge still dominates the market due to its low cost and availability. TiN-thin-film's initial cost is higher, so its advantages are greater at quantities. However, there are benefits even for the small user - and there are more to come. A foil sensor is being developed which can be welded directly on to the carrier. A conventional foil strain gauge is glued on, and has problems with the different ageing process in the different materials (the foil strain gauge has different ageing to the glue, which has different ageing to the sensor-material). After a time, the glue can dissolve: as the pressure is applied to the strain gauge, the glue lifts. TiN-thin-film technology does not have these problems. With the TiN-thin-film technique there is no glue used, and the film is bonded directly onto the sensor material, giving durability and safety. Protective layers may be selected depending on environmental conditions and customer specification; output signal is compensated internally.
Pavenham, Bedfordshire, UK
Telephone: +44 1234 823878
Fax: +44 1234 825331
Smart Pressure Transmitter for Abrasive Media
New Article from Engineeringtalk.com
The chemical, pharmaceutical and similar industries often find that the abrasive, aggressive or high viscosity media with which they work corrode the measurement and control instruments used in the industrial processes involved. Now Jumo Instruments is introducing the dTRANS p02 Ceramic, a smart pressure transmitter designed to overcome this problem. The dTRANS p02 Ceramic combines a corrosion-resistant ceramic diaphragm with a capacitive measurement system and, as an option, the ability to communicate with a central computer using HART communications. This means that it can be set up remotely and can transmit measured data to a central point for combining with other data, analysis and reporting. The dTRANS p02 Ceramic is protected to IP65 for dusty or damp environments, and approved to EN50 081, EN 50 082, EN 55 011 and EN 55 022 (CE mark) standards for use in industrial areas. Jumo's pressure transmitters, including the dTRANS p02 Ceramic, are exceptional in having built-in, microprocessor-controlled temperature compensation. This means that, as the temperature of the medium being monitored changes, the consistency and accuracy of the transmitter remains constant: it permits turn-downs greater than 10:1. The dTRANS p02 Ceramic operates with medium temperatures of between -40 C and +120 C. Values can be transmitted and displayed for input pressure (in 13 differential units or as a percentage), minimum and maximum pressure, sensor temperature, output current, out-of-range and error conditions. As a result of this rich functionality it can be used, not only as a transmitter, but also in place of an additional manometer, indicator or temperature measurement device. The pressure sensor is based on Jumo's well proven pressure sensor technology, which can measure pressures from -1 to +25 bar. Pressure connections are available in many variations to support, for example, clean in place (CIP) requirements. Full HART communications and Jumo's proprietary set-up software are available as options, allowing multiple units to be set up and monitored from a central personal computer. The dTRANS p02 Ceramic has been designed for ease of use and set up: all adjustments are done from the front LCD display and keypad, including range start, range end and zero point. This saves considerable time as instruments no longer need to be opened or removed. All errors resulting from mounting position and environmental influences are automatically included in the set-up, so high levels of accuracy are ensured. The same adjustments can also be made via the HART communications interface, a set-up cable and a set-up program using a PC, which is extremely easy to use. Other features include self-diagnosis of the electronics and sensor, error signalling on the LCD, and alarms by both analogue signal and HART.
Jumo Instrument Co
Harlow, Essex, UK
Telephone: +44 1279 635533
Fax: +44 1279 635262
A Junction Box is Only Useful When it Fits
TURCK's new compact multibox® picofast® 4- and 8- Port Junction Boxes will fit almost anywhere. Designed for space-limited OEM and MRO applications, they feature an exceptionally small footprint, and are available with many options. The new junctions are ideal for small machine and appliance builders, and robotic equipment applications. High-quality picofast 4- and 8- Port Junction Boxes consolidate wiring from multiple switches, solenoids, actuators and other devices, reducing wiring time during equipment installation, replacement, and relocation.
The new cordsets combine a G-style connector body with an extra-long and extra-heavy solid brass coupling nut and CPE rubber cabling, resulting in reliable performance that’s nearly indestructible. The rugged cordsets exceeded SAE requirements during extensive lab and field testing in harsh industrial conditions, and are resistant to wear and tear from weld slag, engine grease, lubricants and cutting fluids.
Designed to solve multi-conductor wiring applications in harsh environments, multifast cordsets and extensions are available in a variety of styles and configurations for use with junction boxes, or as multi-conductor cordsets and extension cords for light curtains, PLCs and other devices. Multifast components include high-flex, shielded cables for EMI/RFI protection, and solid metal connector shells with fully molded connectors for built-in strain relief. PLTC-rated NAMUR models feature blue PVC cable.
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