Basic considerations on analog technology
You want to use Beckhoff devices (terminals, boxes, modules) with analog input or output function. This also includes metrological applications, i.e. applications with the goal of the lowest possible measurement uncertainty, or colloquially, high measuring accuracy.
Then, before the design-in process, but especially at the point of software creation and commissioning, you should take a moment for the following basic considerations:
- Diagnostics
In the event of problems, elements that are not directly relevant to the solution are frequently pushed aside on the path to the solution. However, take your time and program the diagnostic options available in EtherCAT (or other fieldbus used), TwinCAT (or other control software) and devices! Remember that software diagnostics is possible in each of the following levels: - fieldbus/EtherCAT,
- device (terminal, box module, module) and
- analog channel (several per device if applicable)
| which means that at the end of each bus cycle, you have information on whether you can trust the measured value. You should not assume that the measured value is up to date and correct, just because it lies within a plausible range. |
- False measurement – assessing the severity of the consequences
You wish to carry out a measurement. There is a certain (small) probability that this can lead to an incorrect result; refer to the "Diagnostics" section. However, internal or external influences on the measuring device can also lead to an incorrect measurement, e.g. in the form of an unexpectedly high measuring error. For your application, consider whether you can respond quickly enough in this situation, repeat the measurement if necessary, or whether other actions are necessary. A plausibility check of the measured value is usually useful. If there is a considerable potential for damage, a redundant measurement with a second/nth sensor and analog input could be useful and cost-effective. - 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 operational disruptions.
Refer to the chapter "Analog information - shield and earth" - Environmental conditions
In particular, the ambient temperature at the place of installation of the device, in conjunction with air movements (forced ventilation, still 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, such as the failure of cooling units, the incidence of light, or handling of hot parts in the vicinity. If the cooling is expected to fail, for example, a device should be switched off (de-energized) to protect it from damage due to overheating.
Special environmental influences (humidity, temperature, gases) can also lead to corrosion or, more generally, to altered transmission properties of contacts or connectors (including inside the device). Appropriate protective measures may then be required.