Metrology and EtherCAT terminals - basic concepts

You wish to use Beckhoff EtherCAT devices for metrological purposes. In that case you should take a little time to consider the following basic points before Design-In processing, and in particular when creating the software and commissioning:

  • Diagnostics
    In case of problems, that which is not directly relevant to the solution is frequently pushed aside on the road to the solution. Take the time to program the diagnostic options available in EtherCAT, TwinCAT and devices! Remember that software diagnostics is possible in each of the following levels:
    • Fieldbus/EtherCAT,
    • device (terminal, box) and
    • analog channel (several per device if applicable),

 

which means that at the end of each bus cycle you have the information regarding whether you can trust the measured value. You should not assume that the measured value means, that it is up to date and correct, just because it lies within a plausible range.
See also chapter "General commissioning instructions for the EtherCAT slave", among others.

  • False measurement - evaluation of the seriousness of the consequences
    You wish to carry out a measurement. With a certain (small) probability this can lead to an incorrect result; refer also to the section "Diagnostics". But also internal or external effects to the measurement equipment could lead to a false measurement e.g. as a type of an unexpected high measurement fault. For your application, consider whether you can react quickly enough in this situation, or if necessary repeat the measurement, or whether other actions are necessary. A plausibility check of the measurement value is usually meaningful. If there is a considerable damage potential, a redundant measurement with a second/ nth sensor and analog input could be useful and profitable.
  • Shielding and earth
    Consider environmentally dependent influences on the production plant/measurement environment, which can differ significantly from the laboratory and prototype conditions. This can lead to considerable measuring errors and significant operational disruptions.
    Refer to the chapter "Analog information - shield and earth"
  • Environmental conditions
    In particular, the environmental temperature at the place of installation of the device under discussion, in conjunction with air movements (forced ventilation, standing air, self-convection) and the installation position can influence the measurement operation.
    Consider the static and dynamic thermal processes that can take place at different times of the day, e.g. the failure of cooling units, the incidence of light or the handling of hot parts in the vicinity. If failure of the cooling is to be expected, an EtherCAT device must be shut down if necessary to protect it against irreparable damage due to overheating.
    Specific environmental effects (humidity, temperature, gases) could also lead to corrosion or modified transmissions properties of contacts or plug connectors (also inside the device). Appropriate protective equipment would be required then.
    Refer to the technical specifications and the chapter "General information on measuring errors/measurement uncertainty"