wjs
New Member
Don’t let your fancy Digital voltmeter confuse you.
Analog voltmeters have an advantage when working with “power circuits”, as they aren’t so sensitive that they measure induced voltages such as those caused by broadcast radio or TV signals etc., etc. These voltages can be seen with an oscilloscope, and they can be quite large, but they are incapable of supplying much if anything in the way of current. Drain away a few milliamps, and this noise disappears.
Digital voltmeters are high impedance, meaning that they don’t place any load to speak of on the circuit being measured. Place such a meter on the end of an extension cord, along with an oscilloscope, and you will actually see that the meter is measuring the peak voltage on the cord, and some of that voltage is electrical noise. Place a 10,000 ohm resistor from the cord to ground, and the noise will disappear from the oscilloscope screen, and your voltmeter will now give you a more accurate reading of the true available voltage.
Analog voltmeters have an advantage when working with “power circuits”, as they aren’t so sensitive that they measure induced voltages such as those caused by broadcast radio or TV signals etc., etc. These voltages can be seen with an oscilloscope, and they can be quite large, but they are incapable of supplying much if anything in the way of current. Drain away a few milliamps, and this noise disappears.
Digital voltmeters are high impedance, meaning that they don’t place any load to speak of on the circuit being measured. Place such a meter on the end of an extension cord, along with an oscilloscope, and you will actually see that the meter is measuring the peak voltage on the cord, and some of that voltage is electrical noise. Place a 10,000 ohm resistor from the cord to ground, and the noise will disappear from the oscilloscope screen, and your voltmeter will now give you a more accurate reading of the true available voltage.