Overload capacity (measurement technology)

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Measuring devices that are approved for continuous operation must be able to be operated up to the upper measuring range end value without being damaged. If non-damaging operation is also possible, there is an overload capacity. For measuring devices with a scale display that have a class symbol, the limits of the load capacity are specified in DIN EN 60051 . Two types of permissible overloads are specified. The following details are limited to voltage and current measuring devices.

Permissible permanent overload

If the reference conditions are met, the input variable may exceed the end value of the measuring range by a factor of 1.2 (or 20% added together) for a period of 2 hours. After switching off, the zero point may not be shifted by more than 1% of the scale length. After cooling down to the reference temperature, the measuring device must meet its accuracy requirements.

Permissible short-term overload

With this type of overload, two requirements must be met. In this simplified representation, only the overload to which an attentive operator can often react will be dealt with: the one-time overload lasting 5 seconds . The information is only valid for

  • Class 1 or greater devices
  • Devices without rectifiers.

Then an overload is permissible

  • for voltage measuring devices: up to a factor of 2 on the measuring range end value,
  • For ammeters: up to a factor of 10 on the full scale value.

It is taken into account that the electrical energy sources usually supply a constant voltage and a variable current intensity that is dependent on the load, and that false expectations should not occur as easily with voltage as with current intensity.

The second short-term overload capacity is an overload of 0.5 s duration that can be repeated several times. The number, height and time interval are specified differently for different measuring devices.

Deviations from the specifications of the standard may be made if the deviation is specified in the instructions for use and the instructions for use are indicated by means of a scale lettering.