Digital Multimerter, How good is yours?

[chemelec]

Have you ever tried to test a 9 Volt DC Battery on the AC Scale?
Many DMM's will read 18 Volts.
Some read ZERO, as it Should do.

So when trying to measure an AC Signal on a DC Line, It may be Useless.

Maybe its time to get a Better DMM.

Your Comments?

 

[FvM]

Have you ever tried to test a 9 Volt DC Battery on the AC Scale?
Many DMM's will read 18 Volts.

Not impossible but unusual. Surely not many. I never came across this case, can you name a brand and type?

 

[godfreyl]

So when trying to measure an AC Signal on a DC Line, It may be Useless.

You could use a capacitor to block the DC to the meter. It's cheaper than buying a new meter.

 

[Qaisar Azeemi]

for all DMMs; when you measure the DC on AC range you will certainly get 30% to 40% high readings.

REASON: AC meters always measure RMS values of the ac signal (not peak values) .. and RMS values are always DC equivalent or effective values.... so when you measure DC on AC scale the calibration of the meter will display its value 30% greater than the original value.

 

[FvM]

for all DMMs; when you measure the DC on AC range you will certainly get 30% to 40% high readings.

Most digital meters provide AC coupling in AC ranges as far as I'm aware of. If DC coupled, a true RMS meter would give correct reading for pure DC, a meter displaying full wave rectified value calibrated as RMS is high by 11 % respectively the factor pi/(2*√2). Classical analog meters mostly display rectified value.

 

[ALERTLINKS]

Once i studied my meter for same cause. It used half wave rectification for AC. Series resistor with diode were chosen to show calibrated reading. It was obvious why it displayed near double voltage when fed with DC.
Similar to 50% PWM.

 

[FvM]

Yes, I know there are some analog multimeters with half-wave rectifier. I had a Chinaglia Cortina which uses full-wave rectification and shows the said 11% deviation.

The original post was however about DMM. I wondered which DMM brand uses half-wave rectification and DC coupled AC range? Don't say it's impossible.