Safety Rotary Encoder RVK58S : SIL3/PLe
compliant drive solutions, including rotor position detection

Machine and plant engineering companies are increasingly relying on failsafe components to fulfil the safety requirements specified in the current version of the Machinery Directive 2006/42/EC. The safety sine/cosine rotary encoder RVK58S is an ideal choice as it also allows the position of the motor rotor to be detected with the highest accuracy levels.

Only rigorous end-to-end safety concepts are able to truly ensure the required safety level. This means that the capability of a safety solution is effectively only as good as the weakest link in the chain. It has long been common practice to configure important system components redundantly and detect potential malfunctions by comparing corresponding system parameters. Although this fulfils the purpose, it is undesirable in today´s view due to duplication of the costs of equipment and material as well as high installation and cabling efforts. Furthermore, increasing the number of components raises the probability of failure and makes certification of conformity more expensive.

Self-monitoring replaces redundancy
Intelligent self-monitoring is often used now in place of redundancy to ensure proper operation of the various functional units. The new RVK58S sine/cosine rotary encoder from Pepperl+Fuchs Drehgeber GmbH, plays a key role in the development of safe drive solutions. This high-resolution encoder, packaged in a 58-mm housing, has 1024 increments per revolution and boasts a functional safety concept, along with an absolute position track as an extra feature. Signal conditioning is handled by a special ASIC, which also looks after internal diagnostics.

Faults on the incremental encoder disc or errors in the signal path can be detected reliably by using the formula sin²(x) + cos²(x) = 1 to evaluate the incremental sine and cosine signals from the encoder, which are offset by 90 degrees. The supply voltage, temperature, LED drive and calibration data checksum are also monitored. If a violation occurs, the encoder electronics put the outputs in a high-impedance state so that the controller can detect the malfunction immediately by means of its open-circuit detection function. With this feature, the new rotary encoder considerably simplifies the development of safe machines and at the same time eliminates the need for the redundant sensor component approach used in conventional concepts. The sine/cosine rotary encoder is already certified, and certification of the additional absolute position track is currently underway at TÜV. After this certification is issued, the device will be approved for use in drive products that fulfil safety requirements up to SIL3/PLe using only one encoder.

Rotor position detection using a single-cycle absolute position track In addition to the high-resolution incremental tracks, the rotary encoder has a sine/cosine absolute position track with exactly one cycle per revolution. It provides information on the actual position of the rotor in the motor. This information is needed for purposes such as start-up commutation of synchronous motors. The absolute position is output as a digitized signal with 13-bit resolution using either the Synchronous Serial Interface (SSI) or Bidirectional Synchronous Serial (BiSS) interface protocol. With the combination of the sine/cosine interface, SSI and BiSS, the encoder utilizes existing communication paths and eliminates the need for proprietary safety protocols.

In combination with a suitably certified controller, the safety rotary encoder from Pepperl+Fuchs enables single-encoder solutions, eliminating the need to integrate a second encoder to fulfil more stringent safety requirements. However, a prerequisite for this is that both sensor channels are always connected to the controller. With this system configuration, classification at a higher ISO 13849 performance level (PL e) or IEC 62061 safety integrity level (SIL 3) is straightforward. All motor activities are carried out and monitored reliably, enabling the implementation of typical speed-based safety functions such as safe limited speed, safe speed monitoring, safe standstill monitoring, safe rotation direction, safe acceleration/deceleration, and so on.

Safety rotary encoder replaces mechanical safety solutions The innovative safety functions allow conventional mechanical safety devices, which are subject to wear, to be replaced by software functions in many applications. For example, in high-bay warehouses the expensive hydraulic end-stop buffers at the ends of the storage and retrieval machine guideways can be eliminated entirely. In addition, less empty space is needed and the vehicles can be made lighter thanks to lower braking deceleration. In combination with a suitable safety control unit installed either locally or in the drive controller, the RVK58S monitors compliance with the specified braking ramp (safety limited deceleration) as well as the speed of travel (safe limited speed) of the storage and retrieval machine. If any of the configured limits is exceeded, the system is either braked with the aid of the drive or (in case of total drive failure) a mechanical brake in the vehicle is applied.

Safety functions simplify start-up and servicing Machine operators are most likely to be injured during start-up, set-up and servicing, since these activities are usually performed directly in the hazard area. The safety rotary encoder enables the implementation of many extended safety functions that allow these activities to be managed safely with minimal effort.

Summary
Machine manufacturers and operators are obliged to fulfil the safety requirements specified in EN ISO 13849, and the world´s first functionally safe rotary encoder with a supplementary absolute position track makes a valuable contribution to the efficient implementation of safe drive solutions. The RVK58S merges seamlessly with modern safety concepts and makes it easier for machine and plant engineering companies to demonstrate that their products conform to the required performance level (PL) or safety integrity level (SIL). Thanks to the integrated absolute position track, the encoder is suitable for general-purpose use in a wide variety of drive solutions, regardless of whether they are based on synchronous or asynchronous motors.

Pepperl+Fuchs in profile
Pepperl+Fuchs is a leading developer and manufacturer of electronic sensors and components for the global automation market. For more than 60 years, our continuous innovation, high quality products, and steady growth have guaranteed us continued success.

Pepperl+Fuchs - protecting your process
The Process Automation Division is a market leader in intrinsically safe explosion protection. We offer comprehensive, application-oriented system solutions, including customer-specific control cabinet solutions for the process industry. A large portfolio of components is available from our various product lines: isolated barriers, fieldbus infrastructure solutions, remote I/O systems, HART interface solutions, level measurement devices, purge and pressurization systems, industrial monitors and HMI solutions, power supplies, separator alarm systems for oil and petrol separators, signaling equipment, lighting as well as emergency shutdown equipment and accessories.

Pepperl+Fuchs - sensing your needs
With the invention of the inductive proximity sensor in 1958, the company set an important milestone in the development of automation technology Under the motto »Sensing your needs», customers benefit from tailor-made sensor solutions for factory automation. The main target markets of the factory automation are machine and plant construction, the automotive industry, storage and material handling, printing and paper industry, packaging technology, process equipment, door, gate and elevator construction, mobile equipment, renewable energies. The division offers a wide product range of industrial sensors whether it´s inductive, photoelectric or ultrasonic sensors, rotary encoders, identification systems, barcodes, code readers for data-matrix-codes and vision sensors.

For further information, view website: www.pepperl-fuchs.com or e-mail: sales@gb.pepperl-fuchs.com 

Balluff power supply for wind energy equipment

Just in time for the Hanover Exhibition Balluff introduces a new, intelligent, energy-saving power supply especially for use in wind energy equipment. The semi-potted device with an efficiency rating of 93% is designed for high shock and vibration loads and an extremely long service life of nearly 20 years with a MTBF of 800,000 hours. A key feature: this is the first power supply which can be connected directly to the generator voltage without need for an intermediate transformer. Also completely unique are the optical indicators which display the status and condition of the unit. Since it tracks dynamic loads, it can be operated continuously even under high load conditions. This makes reserves of from 30 to 50% no longer needed.

Special sensors in combination with a microcontroller continuously monitor wear factors in the power supply such as temperature, overload, faults and other conditions. Intelligent evaluation of these parameters then gives the user an overview of the status of the unit for implementing maintenance measures, thereby drastically reducing the probability of failure of the overall system. Colored LEDs in traffic light colors provide the user with continuous information about the current load level, the »stress level» as well as the life time, a forecast of remaining life expectancy. The indicators are bright enough to be reliably seen and interpreted from several meters away.

For the first time ever the usual 3-phase transformer used in wind power equipment can be dispensed with, thereby saving money. Thanks to its broad input range of 380 - 690 V the switched-mode power supply can be connected directly to the generator voltage of the wind turbine. The positive effects: installation effort, and reduced number of failure-prone parts along with increased efficiency of the system due to less heat loss.

For further information, view website: http://www.balluff.co.uk or e-mail: sales@balluff.co.uk