Measuring apparatus for measuring a voltage over an isolation barrier and household appliance having the meauring apparatus

A household appliance, comprising:

• a grid connection for connecting the household appliance to an AC supply voltage;
• a measuring apparatus for ascertaining measurement information relating to an input voltage, said measuring apparatus including:
• an operational amplifier having a first input, a second input, and an output for providing the measurement information;
• a first input node for coupling to a first pole of the input voltage;
• a first isolation resistor connecting said first input node to said first input of said operational amplifier;
• a second input node for coupling to a second pole of the input voltage;
• a second isolation resistor connecting said second input node to said second input of said operational amplifier;
• a feedback resistor connecting said output of said operational amplifier to said first input of said operational amplifier:
• a reference resistor connecting said second input of said operational amplifier to a reference potential;
• an analog-to-digital converter configured to convert an output voltage at said output of said operational amplifier or a voltage derived therefrom into a digital measurement voltage;
• and
• a processor configured to use the digital measurement voltage as a basis for:
• ascertaining, as the measurement information, a measurement value for the input voltage;
• detecting a change in polarity and/or a zero crossing of the input voltage;
• and/or
• ascertaining a frequency of the input voltage;
• said measuring apparatus configured to use the AC supply voltage as a basis for ascertaining the measurement information relating to the AC supply voltage;
• and
• a controller configured to operate a function of the household appliance depending on the measurement information.