Datasheet

MCP3901 Low-Cost Power Monitor Reference Design
DS51915A-page 14  2010 Microchip Technology Inc.
2.1.4 Line Frequency Compensation
A 50 Hz line frequency is used, which is the typical frequency most of the time. How-
ever, this is not a constant and can vary above or below this value by a few Hertz. This
line frequency shift can cause measurement errors because of the characteristics of
the Sinc filter at low sampling speeds. The Sinc filter transfer function is similar to a
low-pass filter. Depending on the sampling speed of the ADC, this low-pass filter can
be narrower or wider.
Figure 2-4 shows the following line frequency situations:
• 880 sps (as in this meter)
• 1200 sps
• 3200 sps
FIGURE 2-4: Sinc Filters Transfer Functions.