How to Measure Voltage with Multimeter


D

dlobmwm3

Member
Can anyone assist me in measuring voltage on my track? I am not sure what the heck I am doing and didn't want to blow the new multimeter. I have the following meter.

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The V section in black is to measue low voltage current. Set the dial to 20. Stick the probe plugs into the COM and V holes. Use the metal ends of the probes with one on each rail. You should get a positive voltage reading of around 12-16 volts if the track has power.
 
Like Jim said you'll get a + or - reading for DC, depending on the direction switch. For DCC you'll need the meter set on the red side. Nice little meter by the way!
 
Did this instrument come with instructions, or are they downloadable online?

You must set the correct scale, and have the probes in the correct orifices, as the previous posters have alluded. You don't want the instrument measuring voltage above the sensitivity range you select on the rotary dial because you will get the highest reading, and no discrete resolution. So, if you want to measure 12 volts, you would set the arrow in the correct third of the reading dial, and set it at the next discrete indicated top voltage...in this case, 20. If you are in HO, you should not exceed 19-20 volts.

Note that if you are measuring DCC voltage (AC square waveform), you will get a false voltage reading because your instrument can't deal with that current properly. You need a RAMP meter from Tony's Train Exchange or something equivalent.
 
One additional point. The caveat about not getting an accurate measurement for the square form AC current used for DCC is correct but the meter will still show a voltage reading if the track has power. If the scale reads 0.00, you know the track is dead.
 
True, it all depends on the meter. Digital signals are simply a pulsating DC voltage which most meters will see in the DC mode. The only true reading is with an O scope, but that isn't necessary for what we're doing.
 
hamltnblue said:
True, it all depends on the meter. Digital signals are simply a pulsating DC voltage which most meters will see in the DC mode. The only true reading is with an O scope, but that isn't necessary for what we're doing.
Click to expand...
A DCC signal is not just a pulsating DC voltage but an alternating current. If you try to read the voltage of a DCC signal with a meter set to DC you should get 0 volts(unless you are running a DC locomotive using "zero bit stretching.") You will, however, get a reading with the meter set to AC, although it will not be accurate with most meters.
 
CSX Robert said:
A DCC signal is not just a pulsating DC voltage but an alternating current. If you try to read the voltage of a DCC signal with a meter set to DC you should get 0 volts(unless you are running a DC locomotive using "zero bit stretching.") You will, however, get a reading with the meter set to AC, although it will not be accurate with most meters.
Click to expand...

A DCC signal is not technically an Alternating current, but a bi-polar DC squarewave. The difference being an AC signal has a varying amplitude in time where a bipolar squarewave has a (desired) instantaneous change in amplitude above an below zero reference, from negative to positive. The peak of the squarewave is equivalent to the RMS value ("root mean square" or working voltage) of an AC signal. So, if you have a digital meter that reads AC RMS values, it will give an accurate reading with an AC setting. This is also the theory used in Tony's panel meter.
 
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