ELM3xxx Notes on operation

EMC immunity according to EN 61000-6-2

In order to achieve immunity to electromagnetic interference in accordance with EN 61000-6-2, a digital low-pass filter must be used with which the peak-to-peak (PtP) noise is suppressed to maximally 1/3 of the specified basic accuracy. Such filtering is also useful from the point of view of measurement technology, as the basic accuracy given for the respective terminal is specified "with averaging", i.e. without the influence of white noise. Filtering is not necessary if the unfiltered PtP noise already lies below the 1/3 limit. It may also be useful to do without filtering when fast response times are required. However, it is then possible that the full specified basic accuracy is not achievable in all cases.

Here are two examples of this with fictitious numbers:

• Example 1:
  ELM3004-0000, ±10 V measuring range:
• Noise without filtering E_Noise,PtP < 60 ppm_FSV, basic accuracy ±100 ppm_FSV.
• Because 60 < (1/3 ⋅ 200), no filtering is required.
• Example 2:
  ELM3004-0000, ±20 V measuring range:
• Noise without filtering E_Noise,PtP < 560 ppm_FSV, basic accuracy ±300 ppm_FSV.
• Now 560 > (1/3 ⋅ 600), and a low-pass filter is required if the full basic accuracy is to be achieved.