How does a multimeter measure low frequency AC voltage?
A multimeter measures AC signals by selecting an appropriate AC filter. The lowest frequency that the multimeter can measure is 3 Hz. To make accurate measurements, note the following.
Take care to select the correct AC filter setting. The AC filter smoothes the output of the rms converter, and for signals less than 20Hz, the correct setting should be LOW. With the LOW filter setting, the multimeter automatically inserts a 7 second delay to ensure the multimeter is ready for testing.
If the range of the signal being measured is known, manually setting a range will speed up the measurement time.
The multimeter uses AC coupling to remove DC signals when measuring AC signals. For a signal with high output characteristic impedance, sufficient time is needed to prepare the AC-coupled DC blocking capacitors. The length of this time will not be affected. The frequency of the AC signal affects it, but any change in the DC signal will affect it. This is why a 7 second delay needs to be inserted.
