That's what Positek Ltd. has done with its series of long- and
short-stroke linear induction position sensors (LIPS). Mounted in the sensor
itself, the electronic interface allows oscillation frequencies of up to 2 Mhz.
Traditionally, high-performance inductive position sensors call for coils with many turns of fine copper wire, leading to relatively bulky designs. Such low-frequency designs also require highly-permeable, high-cost target materials, such as nickel- and silicon-iron. Conversely, less bulky coils with lower turn count resonate at high frequency and can use thicker wire. The reduced time period between oscillations, however, makes synchronous demodulation difficult to achieve.
LIPS locks synchronous demodulation to the signal via custom IC, eliminating the potential for measurement errors. This, in turn, allows high-frequency oscillation. Benefits not only include smaller coils and printed circuit techniques, but low-cost target materials like aluminum and stainless steel. "Performance is midway between an encoder and a potentiometer," says John Francis, Positek director. "LIPS durability puts it miles ahead of the pot in life cost, despite being a bit more expensive to start with," he adds.
While encoders offer high accuracy, Francis says LIPS has the advantage of being an absolute device: "Unlike an incremental encoder, a reading is available at switch-on with virtually infinite resolution," he says.
The new design also makes the sensor particularly suitable for use in areas with high magnetic fields. Rotary versions have been developed using similar principles.
John Francis, Positek Ltd., Queen St., Chedworth, Gloucester UK, GL54 4AG, Tel/Fax: +44 1285 720489.
Replicate the sense of smell
Unlike light or sound, the sense of smell is a chemical process with no scale against which the intensity of an odor can be measured. Established methods of measuring smell involve human inspectors or gas chromatography/mass spectrometry. The latter is slow and complex-more suited for a laboratory test than production process-while the former is inconsistent.
Now, researchers at the University of Manchester Institute of Science and Technology (UMIST) have identified a number of conducting polymers that can be used as transducers for selected individual or mixed chemicals. This development work has led to a commercial system made by AromaScan.
"When interacting with volatile chemicals at room temperature, polymers require only microwatts of power, and can be correlated to specific compounds," says K.C. Persaud, who heads the development team at UMIST. He describes the new product's operation as follows:
The instrument draws chemical volatiles from a sample over an array of 32 polymer sensors, each synthesized to be specific to particular classes of compounds. In the process of absorbing the volatiles, the surface of the sensor undergoes a change in electrical resistance.
Signals from all the transducers generate instantaneous data sets, visualized as bar charts. Processing through a neural network permits recognizing aroma patterns and labeling them against standard patterns.
Chris Tullett, AromaScan plc, Electra House, Electra Way, Crewe, Staffs, UK, CW1 1WZ, Tel: +44 1270 216444, Fax: +44 1270 216030.
Interconnect smart sensors
Smart sensors send packets of information rather than mere data. A web of smart sensors, connected to a PC or PLC through a single bus line, lets sensors communicate not only with the PC/PLC, but with each other. Developed by Honeywell's Micro Switch Div., the Smart Distributed System (SDS) concept offers three advantages to machine control:
Increased reliability. The sensor's ability to identify itself and offer information regarding its working status can save thousands of dollars of downtime. Limit switches, for example, can watch for passing parts on a transfer line, and signal the PLC to stop the line when necessary. If the switch malfunctions, the SDS self-monitoring capability enables it to recognize the malfunction and stop the line before a jam occurs.
Low-cost installation. Instead of routing miles of wiring between a raft of sensors and a PLC, SDS employs a wiring scheme in which each sensor connects to a bus line of four cabled wires. The well-established Controller Area Network (CAN) communications architecture, developed by Robert Bosch GmbH in Germany, gives the high speed and small size needed for SDS.
Less complexity. Unlike conventional sensors which send a stream of digital signals back to the PLC, SDS sensors monitor a process. As a result, "the controller doesn't have a flood of data coming into it," says Ronald E. Sieck, vice president of marketing, Micro Switch. Honeywell engineers, therefore, predict that PLC manufacturers will soon simplify their designs, possibly condensing four printed-circuit boards into a single board in some cases.
Marilyn Smit, Honeywell Micro Switch Div., 11 W. Spring St., Freeport, IL 61032, Tel: (815) 235-5731, Fax: (815) 235-5574.
Convert color to analog signals
Color is the reflection of light at specific frequencies. The two most widely-used techniques to measure color involve passing the ambient reflection through colored filters, or generating a light beam and measuring the different quantities reflected.
Sensortek Ltd. employs a different approach. Its color sensor passes the ambient reflection through a diffraction grating, which acts like a prism. The light, split into its component wavelengths, strikes an array of three photo-diodes tuned to red, green, and blue. The diodes, in turn, produce three analog signals proportional to the color level on the blue-green, green-red, and grey scales. The signals are transmitted to a PLC or other control equipment for analysis, processing, and output.
Wade Olsen, technical support manager at Sensortek, explains that the sensor can be tuned to memorize a specific color shade. "The control unit," he says, "provides a digital output each time the sensor sees that particular color."
Additionally, an operator can specify the level of matching from fine tuning to broad banding. By cascading the signal to other controllers, as many as 20 different colors can be measured from each original set of signals. "Manufacturers are already using the sensor in monitoring bread as it bakes, paint as it dries, and for the detection of adhesives, electronic components, and colored textiles," Olsen says.
Wade Olsen, Sensortek Ltd., PO Box 222, Bury St. Edmunds, Sufolk, UK, IP28 6EE, Tel: +44 1284 728150, Fax: +44 1284 728155.
Employ some fuzzy logic
For Omron Corp., sensor development targets smaller size, combined functions, and the addition of self-diagnosing/self-adjusting capabilities. The general direction is what the Osaka-based company calls "microsmart" components. Yoshiaki Niimura, a supervisor in sales development, envisions sensors combined with fuzzy processors, data transmitters, and power controls.
This concept takes form in Omron's new four-channel optical fiber photoelectric switch. The company says the E3X-NM incorporates two industry firsts: connection of four optical fiber sensors in parallel; and, at the push of a button, it determines for itself whether to operate in a through-beam or reflective mode.
A fuzzy logic interface supports the product's mutual non-interference technology. Fuzzy logic inference distinguishes each sensor's own light from the light of adjacent sensors, based on the light waveform. If one sensor detects light from the other sensors, it will slightly vary the timing of its own signal to avoid interference. This feature, says Niimura, allows close bundling of the four sensors.
Omron Corp., 3-4-10, Toranomon, Minato-Ku, Tokyo, Tel: +81 3 3436 7139, Fax: +81 3 3436 7029.
Introduction of the XUB-J and H photoelectric sensors from Telemecanique makes this mature technology available for highly-transparent materials. The new products are sensitive not only to objects in glass or PVC, but also to those manufactured in polyethylene terephthalate (PET), a resin increasingly used for packaging food products.
Claimed as the smallest cylindrical sensors on the market, the XUB-J and H measure just 18 mm x 55 mm (0.7 inch x 2 inch). Maximum sensing distance is 80 cm (31 inch).
Michel Rochon, Telemecanique, Schneider Electric SA, 5, rue Nadar, 92566 Rueil-Malmaison Cedex France, Tel: +33 1 41 29 84 16, Fax: +33 1 47 51 96 71.
Control temperature influences
Dewit Industrial Sensors adapts its technology to industry with its magneto-resistive Quadro-flux® sensor. Built from four permalloy strips connected in a wheatstone bridge configuration, the new sensor reduces unwanted temperature influences (max 120°C). Here's how it works:
An external magnetic field twists the internal field made by the permalloy strip to produce the magneto-resistive effect. The change in resistance affects the balance in the wheatstone bridge. Consequently, a voltage at Vin induces a voltage across Vout in relation to resistor size. Vout changes in relation to the change of the internal resistance.
Because the magneto-resistive effect is fast, the sensor works with frequencies up to 25 khz at 1.5 mm (0.06 in) range. Industrial applications, besides revolution counting, include: recognizing direction using a phase difference between output signals, or by using a high/low signal; and non-contact angle sensing, such as controlling valve position.
Pim Wieske, Dewit Industrial Sensors bv, Beaufortlaan 24, 3768 MJ Soestduinen, The Netherlands, Tel: +31 2155 27568, Fax: +31 2155 27547.
Simplify sensor configuration
Sensor-transmitters that have a small display and keypad can prove difficult to configure. The restricted number of keys on the housing requires a complicated menu structure and multiple key operations. With its Smart Series of sensors, Honsberg solves this problem by including an infra-red transmitter/receiver in the sensor electronics.
There are flow, level, pressure, and temperature sensors in the Smart Series, but, in principle, the electronics section can be matched to any front-end sensor. Honsberg supplies the sensors in a plastic housing, complete with an LCD, four arrow keys, an indicator LED, and an IR transmitter/receiver. Device configuration includes such parameters as limit switch settings, sensitivity, displayed units, zero setting, and linearization.
Either Honsberg or the user can configure the device. However, with only a four-key keypad, this would be tedious. The easier way is to download the complete configuration into the unit's EEPROM, using a hand-held IR transmitter/receiver. A minimum amount of permanently resident boot software handles the IR communication. Additionally, the hand-held unit can interrogate the sensor to change settings, or act as a data logger.
R. Bisek, Honsberg & Co. KG, Postfach 110369, D-42863 Remscheid, Germany, Tel. +49-2191-9672-34, Fax. +49-2191-9672-40.
Integrate linear stroke transducer, electronics
For recording linear distances up to ±8 mm (0.3 inch), Magnet-Schultz builds a carrier-frequency oscillator and output amplifier into its type A WE F 008 line of linear stroke tranducers. Designed like a differential transformer, the inductive tranducers house one primary coil and two secondary coils.
Position of the soft-magnetic core within the coil combination determines the magnetic flux between the primary and secondary coils. The working principle is straight-forward: Placing an excitation voltage across the primary coil induces different voltages in the secondary coils, depending on core position. Because the secondary coils are series-connected in opposing directions, the output signal is linearly proportional to the voltage differential between the two secondary coils.
If the core is halfway between the primary coil and the two secondary coils, the induced voltage is the same in each secondary coil. Phase shifting by 180 degrees produces an output signal of zero. A protective housing allows wet/dry applications.
Magnet-Schultz GmbH & Co., Postfach 1665, D-8040 Memmingen, Germany, Tel: +49 8331 104-0, Fax: +49 8331 104 333.