Test meters

[Boonter]

Thanks, one and all !  My question has been fully answered and I find ALL of the input useful, from the simplest method to the more complex.  What a great tool this forum is !!!

[webenda]

The question was for John but I can't help giving my take on this meter. (Apologies for going first John.) The 6 Function Mini Digital Clamp Meter has a 3 1/2 digit display. The half digit is a "1". So max reading on 20 amp range would be 19.99 Amps. If your train were drawing 2.5 amps the reading would be 2.50. The instruction manual does not state any accuracy for amps ranges. AC Voltage specification is ±1.5% in 5 digits. Whoever wrote that was having a bad time translating between Chinese and English. Correct specification is ±(1.5% of reading + 5 digits) or ±1.5% rdg, ±5 cnt. I suspect the AC Current specification is something like ±(3% of reading + 5 digits). In the case of our imaginary answer of 2.50 amps, 3% of 2.5 is 0.075 and 5 counts is 0.05 so uncertainty of reading is ±(0.075 + 0.05) = ±0.12 amps (using conventional rounding rules.) I have never calibrated this Harbor Freight meter, but the few really cheap H.F. meters I have calibrated met their published specifications.

[marxalot]

John,

I see on the specs for the 6 Function Digital Clamp- On unit the AC amp range is 20-400. Are you measuring amps that high or is the unit's results good for less that 20 amps... maybe sacrificing some accuracy then? Thanks.

[webenda]

lionelsoni

Note that neither of the Radio Shack meters mentioned actually measures RMS voltage.  They take some measure of the AC waveform (probably the average of the absolute value) and then indicate the RMS value assuming that the waveform is sinusoidal.

It might be useful for those looking for a meter to know that most of us get along with inexpensive average responding, rms reading meters. It is sometimes necessary to know the voltage or current we read from a source, such as the CW-80, using these meters may not be equivalent to a DC voltage of the same value, but generally not, for as Gary points out, we usually just need to know if the circuit is broken or if some voltage is there or not.

The key to recognizing a true rms meter (measures dc heating power of the waveform) from an average responding meter is the term "True RMS" in the description of the meter.

These references might be too much information for this thread about selecting a meter, but for those who want to know more about this true rms stuff...

Reference:

http://www.calright.com/products/prod_id/267/agilent_hp_3400a_true_rms_voltmeter_10_hz_to_10_mhz

http://en.wikipedia.org/wiki/Crest_factor

[gunrunnerjohn]

Another very useful item is a clamp-on ammeter, I have one of these.

6 Function Mini Digital Clamp Meter

It will also do the other measurements, but it's claim to fame is being able to measure AC current without breaking the wire, a very handy feature for O-gauge train layouts.

[lionelsoni]

Note that neither of the Radio Shack meters mentioned actually measures RMS voltage.  They take some measure of the AC waveform (probably the average of the absolute value) and then indicate the RMS value assuming that the waveform is sinusoidal.

[overlandflyer]

a VOM is a great piece of equipment, but i've got to admit that 99% of the time i only need to test continuity or a straight on/off indication of voltage.

put a buzzer, a battery and a pair of wires in series and you have your continuity tester (is point A attached to point B?) and an 18V bulb in a socket with an attached pair of wires (or small clips) and you have your voltage sensor (is this track getting power?  when i throw a switch is the siding turning on/off?).

inexpensive & simple to make.

cheers...gary

[webenda]

Boonter,

This is what I use, but do not recommend: http://www.triplett.com/products/analog-testers/detail/6-analog-testers/flypage/25-model-310-c?sef=hcfp

Reasons for not recommending:

o The Triplett 310-C has an RSP of $159.00 and is no better than the RadioShack® 19-Range Analog Multimeter Lionelsoni uses.

o It is easy to read the wrong scale on an analog VOM.

o Current is limited to 0.6 amp DC.

I recommend something more like this: http://www.radioshack.com/product/index.jsp?productId=2103175

Reasons for recommending:

o Auto ranging, no confusion from multiple scales.

o Current to 10 Amps DC and AC rms.

[lionelsoni]

This is what I use and recommend:  http://www.radioshack.com/product/index.jsp?productId=12073432&znt_campaign=Category_CMS&znt_source=CAT&znt_medium=RSCOM&znt_content=CT2032235

[TRAINCAT]

A good digital meter is best. You can get them from 25.00 to 100.00 or more. If money is not an issue, I would buy a Fluke meter. But Home depot has some cheaper models that work just fine.

Roger

[Boonter]

What kind of test meter is best to check electrical problems and such on an  O gage layout>  I am not an electrical engineer by any means so somethiong simple and sirect is needed.  Any brand or model number will be appreciated.