A.C. Voltmeters for track voltage monitoring

[lionelsoni]

Almost all AC meters rectify the waveform and measure the average (the DC component) of the result. This gives a value which is about 90 percent of the RMS voltage of a sine wave; but the meter face is marked to correct for this error.  The method suggested by Spike for making an AC ammeter is good, but will show that 10-percent error when used with a sineusoidal current waveform.  However, since you would be using an otherwise unmodified DC meter, you would have to make the 11 percent correction for yourself.

If your voltage is not a sine wave, an ordinary AC voltmeter can give you a very inaccurate reading.  For example, here is a table I have posted before for the CW80 transformer.  It shows the actual RMS voltage corresponding to what you would read with a voltmeter.  It applies only to a phase-control "transformer" with an 18-volt maximum output--like the CW80.  You can see that the error is nearly 4 volts in the middle of the range.

CW80       RMS

 0             0
 1             2.7
 2             4.4
 3             6
 4             7.3
 5             8.6
 6             9.7
 7             10.8
 8             11.8
 9             12.7
 10            13.6
 11            14.4
 12            15.1
 13            15.8
 14            16.4
 15            17
 16            17.4
 17            17.8
 18            18

[ChiefEagles]

Harbor Freight sells Digital Volt meters for under $5.00.

The A.C. range will give you a two digit measurement.

That is good information.

[spikejones52002]

Harbor Freight sells Digital Volt meters for under $5.00.

The A.C. range will give you a two digit measurement.

It also has a 10 amp range. Place a large bridge rectifier in series and the Amp meter across the D.C. terminals.

[trigtrax]

You can pick up cheap multimeters at Radio Shack that will give you fairly accurate readings of AC Track Voltage.. Using light bulbs or LED's won't work without comparator circuits. Not worth the bother to design or build.

[cruikshank]

Just wondering what you are using for monitoring of AC Track Voltage.  Also we have sections of track we need to setup to about 16 volts using a Cab-1.  Has anyone succesfully used a light bulb or series of LED's  to remotely monitor this voltage, if so what voltage lamp?  Thanks, Dave