UNI-T UT81C Operating Manual page 36

Note
The requirement of Input amplitude "a" is as follows:
When 1MHz:
1MHz:
It is normal to have few seconds run time when
switch from other functions to these functions.
When Hz or duty cycle measurement has been
completed, disconnect the connection between the
testing leads and the circuit under test and remove
the test leads away from the input terminals.
34
300 mV a 30Vrms;
600 mV a 5Vrms
Model UT81C: OPERATING MANUAL