Tuesday, August 18, 2015

CANopen profile for weighing devices. @CANopen #PAuto

The device profile family for weighing devices specifies the CANopen interface including the PDO mapping and the necessary configuration parameter. Part 1 and part 2 have been released CiA internal as Draft Standard Proposal (DSP) in August 2015. Part 3 not yet developed will deal with scale devices, and part 4 is intended for special human machine (HMI) interface and indicator devices related to weighing applications.

• Part 1 of this series provides some general definitions including several legal for trade (LFT) modes. It describes also the data encryption and data exchange procedure. Additionally, the sealing and the password changing procedure are described briefly. Of course, this part specifies some common communication parameter of the CANopen interfaces for weighing devices. Legal for trade (LFT) weighing devices are intended for use in commercial applications, in which products are sold by weight. Often, LFT devices comply with Handbook 44 by NIST (National Institute of Standards and Technology). In the USA, they may be certified under the National Type Evaluation Program (NTEP). CiA 461-1 specifies several LFT modes with and without protection, for example, with CRC signature or Trivium encryption.

• Part 2 specifies the CANopen interface for load cells. Load cells are transducers that generate an electrical signal with a magnitude proportional to the measured force. There are described eight devices classes. The profile specifies several compensation techniques for gravity, inclination, temperature, and movement acceleration. In case of external compensation, the compensation values are mapped into the four default RPDOs. The two specified default TPDOs provide the load cell weight output value plus weight status and alarm information respectively the weight status and the process data random number as well as the process data signature. The configuration parameters include data sample rate and filter settings, for example, for Bessel, Butterworth, or Notch characteristics.

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