Standardized sensor profiles improve safety-related process data

Controller Area Network (CAN) in Automation (CiA) recently released CAN device profiles that aim to standardize safety-related process data.

04/25/2014


Figure 1: A typical CANopen Safety rotational encoder is used in electrical drive applications and mobile machines where the rotation needs to be measured. Courtesy: TWKThe standardized sensor profiles include encoders and inclinometers, which have been updated and released as version 4.0 and 2.0 respectively. Both profiles specify safety-related sensor data and its mapping into safety-related data objects (SRDOs) as defined in CANopen-Safety (EN 50325-5). These specifications are the first ones standardizing functional safety on a device's profile level.

CANopen-Safety is supported by an increasing number of IEC 61131-3 programmable controllers. Up until now, they have mainly been applied to mobile machines. The released CANopen sensor profiles allow interoperability between encoders and inclinometers from different vendors. "The success story of the CANopen device profiles continues also for functional safety," said Holger Zeltwanger, CiA's managing director. "The standardized device profiles simplify system integration, and the machine builder can substitute a product more easily."

Encoders and inclinometers

Figure 2: Linear encoders are often implemented in conjunction with hydraulic actuators. Courtesy: TWKEncoders and inclinometers are used in many machines to measure the angle, the revolution, and the length. Encoders can also be used to measure the speed, which is length divided by time, the acceleration, and the deceleration-or the jerk. The related CANopen device profiles specify the process data to be mapped in normal PDOs.

The inclinometer profile also standardizes the safety-related configuration data. This includes the preset values for the lateral and the longitudinal direction as well as the safety application configuration valid parameter, which is set to valid after the configuration is completed and the configuration signature has been generated correctly. The safety application configuration signature contains standardized checks that protect the safety configuration against unintended changes. This function is double-checked periodically by the safety-related application program. In addition, the standardized safety profiles enable the system designer to exchange products without changing the safety-related application software.

Figure 3: Rotational encoder supporting CANopen Safety and CiA 406 version 4.0 feature interoperability and interchangeability, which is made for safety-related communication. Courtesy: TWKMost of the applications in mobile machines require a Safety Integrity Level (SIL) of two, according to the IEC 61508 standard. The CANopen Safety protocol is suitable for SIL-3, and can also be used for lower levels. CiA has implemented the CANopen Safety protocol in a single micro-controller with two CAN on-chip modules.

Edited by Jessica DuBois-Maahs, associate content manager, CFE Media, jdmaahs@cfemedia.com.



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