First i want to be clear that i do not have a problem with my layout and my question is just to satisfy my curiosity. I wonder if someone can explain to me why when i read the voltage on my DCC layout with a Fluke 115 , a true RMS voltmeter, it indicates about 10 volts and when I use the RRampmeter or any standard voltmeter i get about 14 volts.
Moe Bursztein
I have four, two dollar, Harbor Freight multimeters that measure about 13.6 vac. on my home layout using the NCE Power Cab. The DC for the unit is 13.9 vdc. This tells me the system is on.
At the club using the five amp Power Pro. About the same. My digital Oscope agrees.
I have a forty dollar multimeter and it agrees. Maybe 0.1 or 0.2 vac difference.
Measure the DC voltage to your DCC system and try to make a comparison.
No idea about the Fluke though they are great meters. The past few years we have been told by a few to use a Fluke though no one has ever reported a Fluke reading that I know of.
In a few other forums I have seen about 14 volts with a RRampmeter.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Sounds like mebbe N scale? You don't indicate which scale it is, but that sounds low for HO. My CDN$25 twelve year old unit, digital from ABC Electronics (or whatever it really is) routinely bounces between 13.2-14.7 volts, but that's with a DB150 from Digitrax set on HO.
The Fluke 115 is only good to 1KHz frequency on the TrueRMS reading. (per spec on Fluke's page) ANd even then, 500Hz to 1KHz, it's only 2% + 3 counts. The 115 is more of an electrician's meter, typically no more than 60Hz.
I've been meaning to try my old 8060A - it's good to 25KHz or something. Old though it is, it does work and it checks out on AC and DC volts and resistence against my calibrated standard.
I mentioned in a different thread why, for DCC, which is square wave, a cheap meter that DOESN'T do RMS is probably more accurate, as ones that say just RMS are calibrated for sine waves, which is completely wrong for square wave DCC, and not many True RMS meters go up to DCC frequencies. A sine wave calibrated average reading meter will read high on a square wave.
For Digitrax (not applicable to all others, but may work for some), the recommended way to measure the voltage is to firs make sure address 00 is set to speed 0, or analog disabled, and then measure DC volts from rail A to ground, and rail B to ground (they should be the same or very close) and add them together. This works because of the way Digitrax designed the output stage of their boosters with reference to the circuit common (which they label ground on the front).
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I like to thank you all for taking the time to reply. I consider that my question was answered and save me the trouble in expending $$ for a sofistacated voltmeter.
Moe
rrinker The Fluke 115 is only good to 1KHz frequency on the TrueRMS reading. (per spec on Fluke's page) ANd even then, 500Hz to 1KHz, it's only 2% + 3 counts. The 115 is more of an electrician's meter, typically no more than 60Hz. I've been meaning to try my old 8060A - it's good to 25KHz or something. Old though it is, it does work and it checks out on AC and DC volts and resistence against my calibrated standard. I mentioned in a different thread why, for DCC, which is square wave, a cheap meter that DOESN'T do RMS is probably more accurate, as ones that say just RMS are calibrated for sine waves, which is completely wrong for square wave DCC, and not many True RMS meters go up to DCC frequencies. A sine wave calibrated average reading meter will read high on a square wave. For Digitrax (not applicable to all others, but may work for some), the recommended way to measure the voltage is to firs make sure address 00 is set to speed 0, or analog disabled, and then measure DC volts from rail A to ground, and rail B to ground (they should be the same or very close) and add them together. This works because of the way Digitrax designed the output stage of their boosters with reference to the circuit common (which they label ground on the front). --Randy
Very nice Randy.
Over the past eight years or so in a number of foums I have seen suggestions for using a Fluke for DCC voltage measurements but no results. I have bookmarked this discussion.
I used a Fluke years ago but mostly for DC measurements and maybe 60 or 120 Hz measurements.
Some would say cheap digital multimeters are not accurate.
The real question is - what level of accuracy do you need?
I have about 6 of the HF meters scattered about. i did try one against my reference standard, it's pretty close, granted the reference is at a single AC or DC voltage and a single current level, but it does have 4 precision calibrated resistors in series so you can measure across any 1 or combination of them to check the ohms ranges. The milliamps range (and I would also then say the amps range) of the cheapy is the worst of the lot, AC volts isn't super precise either, but it isn;t even on many expensive meters, DC volts matches the standard - but then it only displays 2 places after the decimal.
But really, what accuracy is needed here? We aren't doing quantum physics, it's a model railroad. Now, you don;t want the meter showing 12 volts when the actual measurement is 18 volts, or vice-versa. But if a cheap meter, a high end meter, and a specialty meter are all within a volt or less of one another - for me I can't justify the specialty meter. The key for most model railroad measurements is that the reading is consistent around the layout. If the meter shows 14.5 volts when it's really 15 - it doesn't make THAT much of a difference as long as you get 14.5 volts everywhere - a drop is a drop, if you have a super accurate device that reads the exact 15 volts and at some distance location you get 14 volts, you have a 1 volt drop. If you have a meter that gives 14.5 volts where it really is 15, and at the far point you get 13.5 - it's still a 1V dropand you know yoou need to work your way back through the wiring to find the cause.
Plus I have the ultimate in measuring DCC signals - a oscilloscope. Being a modern LCD type, it's easily portable (but not battery powered, plus it will show me things no meter will - like the actual shape of the waveform and if I am getting any excessive noise or spikes in the signal. No, I am not recommended everyone using DCC go buy an oscilloscope, it's overkill, but I use it for other things.
rrinker The real question is - what level of accuracy do you need? I have the ultimate in measuring DCC signals - a oscilloscope. Being a modern LCD type, it's easily portable (but not battery powered, plus it will show me things no meter will - like the actual shape of the waveform and if I am getting any excessive noise or spikes in the signal. No, I am not recommended everyone using DCC go buy an oscilloscope, it's overkill, but I use it for other things. --Randy
I have the ultimate in measuring DCC signals - a oscilloscope. Being a modern LCD type, it's easily portable (but not battery powered, plus it will show me things no meter will - like the actual shape of the waveform and if I am getting any excessive noise or spikes in the signal. No, I am not recommended everyone using DCC go buy an oscilloscope, it's overkill, but I use it for other things.