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Using a Multi-meter

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Using a Multi-meter
Posted by SpaceMouse on Thursday, October 15, 2020 5:38 PM

I have two multi-meters. One I can do simple things like check continuity, test battery viability, and check track voltage. The other is just a bunch of 20s.

 Of the settings on the left multi-meter, which are useful for model railroading and what can I test with them.

AND someone suggested I could use an Ohm meter to determine which wire is which on a DCC decoder harness that had all black wires. How do I do that?

 Thanks in advance.

Chip

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Posted by rrinker on Thursday, October 15, 2020 6:26 PM

 The one on the left, DC 20V and AC 200V are the most useful, AC for track voltage, or DC if you use the Digitrax method of measuring between Rail A and GND, and Rail B and GND and adding them together.

 The diode symbol range MIGHT test LEDs (most cheap meters won't light them up though - better ones will light the LED when you have the polarity correct).

 You can use the 200 ohms range for continuity tests, doesn't look like that one has a bepper or anything though so you have to hold the wires on the probes AND look at the display. The meter on the right has a continuity mode which will beep and/or flash the light when there is continuity, so you can focus on touching the probes to the wires.

 The 10 amp range can be used on DC with a DC powe rpack to test the current draw of a loco before putting in a decoder.

 The one on the right, you can just select DC volts or AC volts and it automatically adjust the range.

                                     --Randy


Modeling the Reading Railroad in the 1950's

 

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Posted by ATLANTIC CENTRAL on Thursday, October 15, 2020 6:31 PM

SpaceMouse

I have two multi-meters. One I can do simple things like check continuity, test battery viability, and check track voltage. The other is just a bunch of 20s.

 Of the settings on the left multi-meter, which are useful for model railroading and what can I test with them.

AND someone suggested I could use an Ohm meter to determine which wire is which on a DCC decoder harness that had all black wires. How do I do that?

 Thanks in advance.

 

I would have to teach this course in person. It would be helpful to know how much you know about electronics and basic electrical systems to know were to start.

We could start with the light bulb, switch and battery on a board, but it might take a while to get to tracing out locomotive wiring.

An ohm meter function is generally just going to be used as a conitinuity tester to trace out locomotive wiring.

Sheldon

    

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Posted by SpaceMouse on Thursday, October 15, 2020 6:52 PM

Sheldon
I would have to teach this course in person. It would be helpful to know how much you know about electronics and basic electrical systems to know were to start.

I had a high school electronics class in high school and was fairly proficient in TV repair--e.g. cleaning the contacts on the tuner. In my physics class, I got my homework done while the teacher was expalining to the class how to do the assignment. She let me do electronic "projects" in the back of the class while the rest of the class did the school work. 

Sheldon
We could start with the light bulb, switch and battery on a board, but it might take a while to get to tracing out locomotive wiring.

Let's assume that I can already hard-wire a decoder and isolate the motor--that includes the resistors for the LEDs. But even though Ohm's law is a simple linear equation, for some reason I can't seem to find the size resistor I need. But I have a zillion 3v LEDs and as many 1K resistors, so I'm set.

Sheldon
An ohm meter function is generally just going to be used as a conitinuity tester to trace out locomotive wiring.

 

I was afraid you say that.

So if I touch a lead to the right side track, I just poke around at black wires on the harness until one beeps. This I will call red and and I will even paint the end red.  

 

 

Chip

Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.

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Posted by ATLANTIC CENTRAL on Thursday, October 15, 2020 7:02 PM

SpaceMouse

 

 
Sheldon
I would have to teach this course in person. It would be helpful to know how much you know about electronics and basic electrical systems to know were to start.

 

I had a high school electronics class in high school and was fairly proficient in TV repair--e.g. cleaning the contacts on the tuner. In my physics class, I got my homework done while the teacher was expalining to the class how to do the assignment. She let me do electronic "projects" in the back of the class while the rest of the class did the school work. 

 

 
Sheldon
We could start with the light bulb, switch and battery on a board, but it might take a while to get to tracing out locomotive wiring.

 

Let's assume that I can already hard-wire a decoder and isolate the motor--that includes the resistors for the LEDs. But even though Ohm's law is a simple linear equation, for some reason I can't seem to find the size resistor I need. But I have a zillion 3v LEDs and as many 1K resistors, so I'm set.

 

 
Sheldon
An ohm meter function is generally just going to be used as a conitinuity tester to trace out locomotive wiring.

 

 

 

I was afraid you say that.

So if I touch a lead to the right side track, I just poke around at black wires on the harness until one beeps. This I will call red and and I will even paint the end red.  

 

 

 

Sounds like you are much smarter than you think.

Sheldon

    

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Posted by rrinker on Thursday, October 15, 2020 7:12 PM

 There's one piece of the LED equation that is just experience. That is - picking the current. There is a specification for the LED, but that is a maximum. You want something less. How much? Really it's experience that leads to a good value. Or you just keep solving the Ohm's Law equation for current using different resistor values until you see an amp value that looks good. Experience is what makes me say 9 to 10 milliamps is a good value. So if you know any 2 of the 3 values, you can figure out the missing one using Ohm's Law. There's nothing else to it, no 'tricks' to read into it, it's just the math. 

                             --Randy

 


Modeling the Reading Railroad in the 1950's

 

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Posted by gregc on Thursday, October 15, 2020 7:15 PM

SpaceMouse
 Of the settings on the left multi-meter, which are useful for model railroading and what can I test with them

with the one on the left, you generally select the range that gives you a value within that range and isn't too small.   you might start at the highest range until you reach the range your value is in.

the one on the right auto-ranges and will be easier to use.    the diode setting vs continuity, is suppose to test with a voltage that exceeds a diode drop (~0.7V) for checking transistors or diodes.   but many LEDs require > 3V

greg - Philadelphia & Reading / Reading

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Posted by RR_Mel on Thursday, October 15, 2020 7:28 PM
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Posted by SpaceMouse on Thursday, October 15, 2020 10:34 PM

Thanks everyone. Mel--those probes look interesting.

Let me rephrase the question. Under what circumstances would using the full-featured meter be an advantage?

 

Chip

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Posted by Overmod on Thursday, October 15, 2020 11:10 PM

SpaceMouse
Let me rephrase the question. Under what circumstances would using the full-featured meter be an advantage?

Cutting to the chase, many of the settings on a full-featured multimeter are out of the range of voltage or current to be expected in model railroading.  It is unlikely that you will need the special 10A terminal, for example, or that most of the 750V range would be useful; personally, I don't often need the ranging precision in multiple decades of DC voltage spec (they are on that dial, in part, to reduce the number of expensive digits in the numerical display).

It is interesting to speculate what a purpose-built multimeter for DCC model railroading would include -- much more auto ranging for DC and AC, but also some features of both logic probes and oscilloscopes...

One thing I should note that is a kind of 'pet peeve': the diode test feature is almost dangerous without specifiable voltage and perhaps current limiting.  This applies in spades to LED testing where (as noted repeatedly in these forums) the reverse tolerance for many diode devices is not great.

I read an amusing story many years ago about some poor sap who had a defective lot of fast-blow fuses -- every one he tested for continuity with his meter was bad!LaughLaughLaugh Dunce 

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Posted by trainnut1250 on Thursday, October 15, 2020 11:58 PM

Chip,

I have the meter on the right. You are Mr. Frugal. LOL!! It was the least expensive meter I could find many years ago.

Used it for nearly 30 years before buying a better one. It works great for voltage and continuity but it eats expensive little batteries if you forget to turn it off. 

 

Guy

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Posted by rrinker on Friday, October 16, 2020 8:02 AM

 Well, they are both full featured meters. One just has some more capbilities in one area, while the other has more capabilities in a different area. The one on the right has auto ranging, which is a feature, not a limitation of less options on the knob. The one on the left has a 10 amp range for higher currents that the one ont he right does not have.

 A 'fully featured' handheld meter would be more like my Brymen BM235 which has a full array of ranges, plus peak hold, relative mode (I can set a base voltage or current and then see what the reading is realtive to that level, instead of relative to 0), dual display (can display both the AC and DC volts at the same time), it blinks the back light as well as beeps for continuity, has a diode test that can light LEDs, has a capacitance range to test the value of capacitors, data recording (it can take multiple measurements over time automatically), and true RMS that cna handle a variety of waveforms for AC, not just simple sine waves. That last actually makes it LESS accurate on DCC track than say the cheaper Harbor Freight meter. 

 By that standard, both those meters are basic ones. And that's all you need for model trains. You don't need a fancy meter like mine (and by electronic standards, mine is more of a mid-range model, not a top end one by any means) for use on a model railroad layout. That's why I usually recommend those cheap Harbor Freight ones for someone who wants a meter to use with trains. They work, they are fine at train layout voltages, and are simple and cheap. Just don;t try to measure house voltages with one. And I've seen hobby shops and train specialist places selling the very same meter that HF sells for $5 or less for as much as $15-$20 - more of that model train markup, like DCC power supplies - the newest ones are nothing more then generic laptop power supplies, yet they cost $60+ and you can find the same thing on Amazon for < $25. 

                                     --Randy

                                                


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Posted by RR_Mel on Friday, October 16, 2020 9:39 AM

The cheapo meters off eBay have served me well.  The A830L (I have two) has been extremely accurate, so accurate that I rarely get out my Fluke 179 anymore.  The A830L has hold also with an illuminated screen

I think I gave about $6 for my A830L meters.  Actually the HFT cheapos are pretty darn accurate too.


Mel



 
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Posted by rrebell on Friday, October 16, 2020 9:48 AM

Still have my meter that I got in the 70's, very expencive back then. Never learned to do much on it though, always used my separate continuity tester for that aspect.

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Posted by richg1998 on Friday, October 16, 2020 10:19 AM

What I have used for some years. Compares well to expensive meter and Scope.

I have four. One in car. One for DCC amp meter.

http://www.trainelectronics.com/Meter_Workshop/index.htm

Measuring motor current for unknon motors

http://www.trainelectronics.com/Meter_HF/index.htm

You have everything already explained to you. A Scope would be nice, maybe.

Good luck. I had a Velleman digital Scope and a TEK 385 dual trace. Finally sold both. Amazon sells the Velleman.

Rich

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Posted by rrinker on Friday, October 16, 2020 11:15 AM

 A scope is probably far beyond anything Chip would need. My least used item on my bench - but every electroncis bench needs a scope, right? I've hardly used it, even doing my circuit designs, let alone for train things. Totally pointless for basic track troubleshooting and decoder installs.

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

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Posted by SpaceMouse on Friday, October 16, 2020 11:38 AM

Thanks everyone. 

I remember using a scope in high school. Can't remember what for. Maybe a TV picture tube and adjustiung the coil or something. 

My only complaint with the small multi-meter on the right is that if I've been doing neggly stuff all day, it's sometimes hard to turn the knob to turn it off and on. 

Chip

Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.

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Posted by richg1998 on Friday, October 16, 2020 11:42 AM

I used it at the club layout looking for spikes, Saw none.

I did a lot of projects at home. Carry over from NASA job where I got the TEK by bidding on used equipment.

The Velleman was portable and more usefull. Digital untill I stopped modeling trains.

Rich

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Posted by RR_Mel on Friday, October 16, 2020 12:00 PM

I sold my Tektronix 456 & 545 scopes two years ago (bought train stuff) but for some reason kept the 321 ??? smaller and easier to store.

I bought one of those tiny scope kits (DSO138) and it works pretty darn good, I’ve used it several times working on Arduino stuff.  It’s so small it gets lost on my workbench.




Mel



 
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Posted by rrinker on Friday, October 16, 2020 1:07 PM

 What I find to be more useful in my Arduino projects is one of those inexpensive USB logic analyzers - I cna monitor 8 pins at a time and watch the states change, or with my IO extenders, watch and decoder the SPI data. This thing was insanely cheap - the only extra I bought was a set of the small clip leads to make it easy to clip on to the pins to be monitored.

 This is actually one of the more expensive ones - there are plenty under $10:

https://www.amazon.com/HiLetgo-Analyzer-Ferrite-Channel-Arduino/dp/B077LSG5P2/ref=sr_1_7_sspa?dchild=1&keywords=usb+logic+analyzer&qid=1602871502&sr=8-7-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUFGTEdMNkk2NkRNOE0mZW5jcnlwdGVkSWQ9QTA4NzM0NzUyNzZTWkkwSkJaWjE0JmVuY3J5cHRlZEFkSWQ9QTA5NzQwODczUTlXOUpVSThGUFlOJndpZGdldE5hbWU9c3BfbXRmJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

No, Chip, you don't need one of these. 

My biggest problem is USB ports - Despite 6 on the case of the computer/motherboard, I have already added a 4 port USB card - my scope has USB, one of my bench multimeters also connects via USB, I have 2 different connections for Arduinos (most Unos use a type A, the Nanos have a mini C or whatever), the logic analyzer, USB microscope camera, keyboard, mouse, and when I get my model bench portion up and running, there will be at a minimum one needed for my PR3 and one for the Lokprogrammer. Some things will work through a hub, plus there is another card slot so I could put another card like the 4 port ones I have (which uses a molex connector to the power supply so it can provide 2A charging, not that I need that). 

                               --Randy

 


Modeling the Reading Railroad in the 1950's

 

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Posted by richg1998 on Friday, October 16, 2020 1:18 PM

If you ever think you want a DCC amp meter, I made two some years ago. They tripped at 4.97 amps on the NCE Five amp booster at the club. I had a heavy duty Rheostat as a load for a few seconds. Two three terminals devices do the conversion.

http://www.circuitous.ca/DCCammeter10.html

Rich

 

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Posted by rrinker on Friday, October 16, 2020 1:42 PM

 That is a lot cheaper than the specialty product (there are now two, the RRAmpmeter isn't the only one now). I'd like to see inside a RRAmpmeter - bet it uses the same IC!

 ANother cheapy way, especially if you want readouts for a larger setup with multiple boosters, is to either use HF meters, or those cheap digital volt and ammeters you can get on eBay, and use one of these circuits as the standard to calibrate against. 

 I'm still thinking how I want to do this. I'm not sure I want the displays on the fascia, I'd rather keep that clean with just a track diagram and locla turnout controls. But a set of meters on every booster - or even better, on every power district after the breakers, would be neat. Maybe I'll go next level - build the circuit into an Arduino thing where they all report back to a master so I can have a sensor for each booster plus each power district, and be able to monitor whichever one I want, without stacks of displays all over the place. I kind of want to do manual resets for the breakers, and remote indicators as well, maybe I could turn this into a centralized power monitor panel.

                                       --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by SpaceMouse on Friday, October 16, 2020 3:18 PM

rrinker
 I'm still thinking how I want to do this. I'm not sure I want the displays on the fascia, I'd rather keep that clean with just a track diagram and locla turnout controls. But a set of meters on every booster - or even better, on every power district after the breakers, would be neat.

You could have your display set back a little under the benchwork and have it roll out on a drawer when you need it. 

Chip

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Posted by rrinker on Friday, October 16, 2020 7:49 PM

 Yes, the simple way would be to just put them on the shelves holding the booster under the layout. But then I'd have to go looking.

                                            --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

  • Member since
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Posted by SpaceMouse on Saturday, October 17, 2020 6:32 AM

rrinker

 Yes, the simple way would be to just put them on the shelves holding the booster under the layout. But then I'd have to go looking.

                                            --Randy

Then mount them above you. You can pretend you're in a geek version of a sports bar. 

Chip

Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.

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Posted by rrinker on Saturday, October 17, 2020 11:42 AM

Double deck layout - the valance for the lower deck is the fascia for the upper deck. 

In reality, I'll probably just not meter all those connections anyway - I have yet to really need that.

I once saw an article where the layout owner made a nice cabinet, held the command station and two boosters, plus had volt and amp readouts for all three outputs. But that defeats one of the reasons for adding boosters - distributing the power to keep the bus lines shorter. 

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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