digital voltmeter conection for power supply

[little_carlos]

Hi, im trying to use a digital multmeter as a voltmeter for my powersupply
im using a 8v voltage regulator for supply the multimeter, when i measure something, like a 9v battery, it does fine, but when i try to measure voltage from the powe supply, just dont show anything, what im i doing wrong?

[Richard Crowley]

Typically, DMMs require ISOLATED power. If you try to power them from what you are measuring, it may distort the measurement, or, even worse, it may damage the internal circuit of the DMM.  NOT RECOMMENDED!

Note that there some newer-generation digital panel meter modules which advertise that they CAN measure voltages in common with their power source. But they are specially designed to be able to do that.  Absent any clue of which DMM you are asking about, it seems quite likely that your unit requires ISOLATED power.

Those common-connection tollerant digital panel meters are so dirt-cheap that you could probably get a dedicated meter for your PS for less than it would cost to provide an isolated power supply to your DMM.

[little_carlos]

well, now i undertand why, thanks man