If you want to check the peak voltage of the signal to change at any time. Measuring with a multimeter will not do it. We recommend this circuit. It may help you.
We use this circuit The op-amp IC number CA3140 is the main equipment, acts as a voltage sensor that is accurate.
So It is precision peak voltage detector circuit, and it remembers voltage value in a long memory time.
In this circuit is used with a positive signal input, when has negative feedback only. And the inverting input can only get some feedback, when diode D1-1N4148 is forward biased. When we put the input signal is positive, the output voltage of op-amp increases equal to the inverting input signal.
In working, the capacitor C1 is charged to maximum voltage.
When the input is negative, the diode D1 will be reverse bias, the still voltage on the capacitor C1 but it is discharged slowly with an input current of the op-amp IC1 about 10pA.
Thus, this circuit can monitor a maximum (peak) voltage of more voltage signal and to remember them. For the following it with a multimeter.