Position sensing: encoders, transducers, position controllers

Recent position sensing technologies include an integrated circuit for encoders, an incremental encoder, transfer transducers, dual-channel controllers for linear variable differential transformers (LVDTs), measuring device, wide-angle area sensors, and a cable-extension sensor.

By Control Engineering Staff May 26, 2005

Recent position sensing technologies include an integrated circuit for encoders, an incremental encoder, transfer transducers, dual-channel controllers for linear variable differential transformers (LVDTs), measuring device, wide-angle area sensors, and a cable-extension sensor. Manufacturers include austriamicrosystems, Baumer Electric, HBM, Macro Sensors, Mahr Federal, Sharp Microelectronics, and Space Age Control.

A low-cost 8-bit incremental magnetic rotary encoder integrated circuit (IC) from austriamicrosystems is designed for cost-sensitive industrial and automotive applications. AS5035 is particularly well suited for use in human-machine interface (HMI) applications, such as front panel switches, or as an alternative to optical encoder-based applications, where dust or other particles could severely diminish system reliability and accuracy. AS5035 provides incremental quadrature A/B output signals and an index output signal. The index signal represents a mechanical reference point, called the zero position, which can be programmed by the user at the system assembly stage. Operation safety is ensured by continuous monitoring of the magnet presence and the optimal magnet position in the system. The AS5035 provides 64 pulses per revolution on each of two quadrature output channels, which equals a resolution of 2.8 degrees per step over a full turn of 360 degrees. Failure detection feature ensures safety as it monitors the magnet’s placement during operation. In case of a missing or loose magnet, the device instantly provides a warning signal. The IC operates at rotational speeds up to 10,000 revolutions per minute, without missing any incremental pulses; user can program zero position. AS5035 operates at 3.3 V or 5 V. It oper-ates at -40 to 125 °C. Baumer Electric repackaged a magnetized rotor and sensor in a 58-mm hollow shaft encoder housing to make the EcoMag , an extremely rugged and economical incremental encoder based on a proven magnetic technology. By doing away with the impulse disc and associated optical transmitter and receiver, the encoder can withstand 30g vibration (6 ms) and 100g shock (10-2000 Hz). In comparison: optical encoders typically achieve 10g vibration and 50g shock. Impulse counts of 64 to 2,048 are standard, with higher resolutions possible on request. Maximum output frequency is above 400 kHz, allowing high speeds up to 8,000 rpm. Operating temperature range is -20 to 85 °C (also -40 °C as an option).

HBM Top-Z30 and Top-Z4A transducers cover nominal (rated) forces of 100-500 kN.

HBM ’s latest Top Transfer Transducers give improved accuracy for checking calibration equipment with a repeatability of up to ten times better than required by the ISO 376 force cali-bration standard. National metrology institutes use transfer transducers to compare the precision of different force calibration machines ensuring complete accuracy during routine checks. During tests at the German Metrology Institute, measurements of the transducers showed accuracy to within 0.002% over a year. Top-Z30 and Top-Z4A cover nominal (rated) forces of 100-500 kN. Both can be used for compressive and tensile loading, and force application parts are available. German Calibration Institute (DKD) certificate is included. During calibration tests, it is important that the transducer is connected to a high precision amplifier. HBM recommends its DMP40 precision amplifier for accuracy of 0.0005% and resolution of 2-million digits.

New controllers from MacroSensors can provide servo-position feedback or measure expansion of turbine cases.

Macro Sensors introduces two new six-digit, dual-channel controllers for applications involving LVDT-based displacement transducers or VR half-bridge gauging probes. Economically-priced, the DMC-A2 Dual Channel AC-LVDT Controller and DMC-D2 Dual Channel DC-LVDT Controllers perform arithmetic calculations between two channels for T.I.R. measurements or differential measurement for use in production lines to automatically gage products for quality control and product sorting. In the power generation and petrochemical industries, these controllers can be used to provide servo position feedback on actuated equipment, such as valves and dampers, or for measuring turbine case expansion. The NEMA-4 front panel allows units to be used in marine and offshore mining applications. The digital controllers incorporate a scrolling display that actively prompts users to input information into the unit during specific set-up stages. Users can also view and program data to the controller through a computer using a GUI interface via RS-232 or TCP/IP communications. Power is standard 120 V ac or optional 24 V dc. DMC-A2 Dual Channel AC-LVDT Controller is $925; DMC-D2 is $975.

MarVision MS 442 multisensor measuring machine from Mahr Federal serves applications that require multiple modes of inspection.

Mahr Federal MarVision MS 442 measuring machine incorporates a CCD camera, TTL laser, and mechanical touch probe sensor to provide precision measurement in a robust design for near-production line and work cell environments. Open-architecture style software in the MS 442 provides advanced measuring capability and supports the development of custom-tailored Graphical User Interfaces (GUI) to facilitate operator use. MarSoft Vision 3D software for Microsoft Windows 2000 provides: 2D and 3D geometric elements and functions, form and position tolerances, feature material conditioners, automatic teach mode, and optional CAD-interface for automatic program generation. For stability, MS 442 includes a measuring table and cross-axis of rigid granite. All axes have precise roller bearings and backlash-free dc servo drives. Stage positioning at 250 mm/sec and 0.1

Sharp’s Wide Angle Sensors are prices at $24 in 1,000 quantities.

Sharp Microelectronics says its 5-beam Wide Angle Sensors represent an industry first, combing wide-area sensing with triangulation capabilities to provide extreme reliability, little energy con-sumption, continuous distance reading, and low reflective interference. These RoHS-compliant sensors feature a 25-degree wide measuring angle and come in three detection ranges from 4 cm to 300 cm. RoHS stands for Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS) Directive (2002/95/EC), which is scheduled to take effect July 1, 2006. An improvement over current methods of using multiple sensors for distance detection and ranges, the sensors will reduce an overall bill of materials because one sensor can now take the place of 4 or 5 average sensors. This provides engineers with design flexibility and can save on-board space. Because these sensors contain wide area sensing and triangulation capabilities, they can track movement in the field of view. In addition to the unique ability to detect object movement in a radial matrix, future enhancements might include passive infrared capability to distinguish between animate and inanimate objects.

Space Age Control model 62-60 position transducer is a rugged means of measuring up to 85-in. (2,159 mm). These all-environment miniature displacement transducers are also referred to as draw wire transducers, string pots, string encoders, cable extension transducers, and yo-yo pots. Complementary to LVDTs, encoders, linear potentiometers, and related displacement sensors, these position transducers are noted for small size, rugged performance, accuracy, repeatability, flexible mounting, and easy installation.

—Mark T. Hoske, editor-in-chief, Control Engineering, MHoske@cfemedia.com