250BOB Posted January 26, 2014 Share Posted January 26, 2014 I have had a Multimeter for over 15years......and only ever used it to check the 12v Leisure battery on my caravan. After that......I havent got a clue how to use use it. What useful purposes can a multimeter be used for on a DCC layout.? And what settings are to be used on the Multimeter when using it for checking such things as track voltage etc., on a DCC layout. Thanks....................Bob Link to post Share on other sites More sharing options...
RMweb Gold RFS Posted January 26, 2014 RMweb Gold Share Posted January 26, 2014 The nature of the DCC signal means that it's not possible to accurately measure voltages with a simple multimeter. What you need is a specialist one like the RrampMmeter produced by DCC Specialities and available from DCC Supplies. Not cheap though ... http://www.tonystrains.com/technews/rrampmeter.htm http://www.dccsupplies.com/shop/product_info.php?products_id=316 Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 As above - a multimeter is useless for directly measuring DCC track voltage. However, if you measure the max DC voltage a decoder outputs when attached to the track, it will be about 10% under the DCC track voltage Link to post Share on other sites More sharing options...
Nigelcliffe Posted January 26, 2014 Share Posted January 26, 2014 What RFS says is true, but you can measure useful stuff with a normal cheap multimeter. Resistance scale, (or continuity tester if it has one). Check the resistance of wiring between two places; usually looking for almost zero (proper conductivity) or infinity (proper insulation). Something inbetween suggests a problem which needs investigating. Track voltage approximation. Method 1, measure the AC voltage; its not accurate as RFS says, but your meter may still gives a value which can be compared. Method 2, put a rectifier (one four-pin component, or four diodes to make one) on the DCC track signal, and measure the DC voltage. Make an allowance for the rectifier (about 1.2V) and the figure will be fairly accurate. Checking stuff; if a motor or a bulb/LED isn't working, then a DC voltage check across the two connections will show whether there is any power present. If power is present, motor/LED/bulb is faulty, if power not present, then investigate why... More generally with model railways, I use an analogue meter for current measurement when testing locos on DC, any flicker in the needle indicates a mechanical tight-spot. (Cheap) Digital meters don't respond fast enough for this purpose. Link to post Share on other sites More sharing options...
trisonic Posted January 26, 2014 Share Posted January 26, 2014 I think maybe he wants a glossary for the symbols on the multimeter to the jobs performed.... Best, Pete. Link to post Share on other sites More sharing options...
Phil S Posted January 26, 2014 Share Posted January 26, 2014 Actually, a 'high quality' digital meter such as from FLUKE® will give accurate readings of the dcc track voltage - matching those of an oscilloscope: But at a price of an expensive sound loco you may not be willing to pay just for this limited application: The RRampmeter, at 1/10th that price provides continuous display of dcc (or dc) track voltage and current - extremely useful. However, ANY digital multimeter COULD be used for dcc track measurement with the cheap additon of a 'diode bridge' to rectify the track signal as it passes through the meter (without affecting the actual on- track signal. Such a cheap multimeter could be reserved for dcc track voltage measurement..... An 'off-the-shelf' bridge rectifier (4- leg device intended normally for 'mains' rectification with 2 AC INPUT connections and +ve and -ve connections, could be connected to the Digital Meter, used in DC mode: The indications will be about 1.4V lower than track voltage, and therefore the same as the rectified voltage inside a decoder [matching the value obtained by measuring between the BLUE wire (common +ve) and a decoder ground.... and therefore, in turn, about 1.4V more than the MAXIMUM possible motor voltage after going through the driving power stage (and some people think dcc track voltage should be 12V !!!). Some others may point out that eg such a 50V rating bidge designed for mains rectification will not switch fast enough for the dcc signal ... but it will do no damage to anything, especially if nothing is happening on the layout other than testing voltages. A 'faster' bridge could be made by assembling 4 1N4148 signal rectifier diodes together, correctly, but with a low current limit - but no problem if only used for voltage measurement. Link to post Share on other sites More sharing options...
Crosland Posted January 26, 2014 Share Posted January 26, 2014 Another way to measure the track voltage is between the blue wire and a function output that is on, and add a couple of volts. Andrew Link to post Share on other sites More sharing options...
trisonic Posted January 26, 2014 Share Posted January 26, 2014 I'll put up a photo of the face of one of the cheaper Fluke's later if he doesn't. There's a couple of functions on it I'd never use - unless someone knows better......... i'm no electric's guy either, I'm afraid, but am willing to learn. Best, Pete. Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 Not all of the Fluke MMs can measure DCC directly, their sample rate and RMS converters just aren't up to measuring ~10KHz signals. Link to post Share on other sites More sharing options...
trisonic Posted January 26, 2014 Share Posted January 26, 2014 Not all of the Fluke MMs can measure DCC directly, their sample rate and RMS converters just aren't up to measuring ~10KHz signals. No point in writing that unless you know what models do and what ones don't...... Best, Pete. Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 The specs are all on their website Link to post Share on other sites More sharing options...
trisonic Posted January 26, 2014 Share Posted January 26, 2014 If you understand how to relate them to DCC - a lot of people do not......... Best, Pete. Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 Sure, I guess my point is that spending £500 on a MM to measure DCC track voltage directly to within a few % is unnecessary. If you need this kind of accuracy it will be for designing and testing DCC equipment and you will already have a bench scope to hand. As DCC users we can just measure the DC output from a decoder with a £50 MM and add 5-10% to get the track voltage. Link to post Share on other sites More sharing options...
trisonic Posted January 26, 2014 Share Posted January 26, 2014 Why don't you go back and read the OP? Maybe you can help him........................ OK back with better photo of symbols (how to use in relation to testing DCC) for those that can help the OP: By the way this Fluke is about $140.00 in the USA. Best, Pete. Link to post Share on other sites More sharing options...
Nigelcliffe Posted January 26, 2014 Share Posted January 26, 2014 Sure, I guess my point is that spending £500 on a MM to measure DCC track voltage directly to within a few % is unnecessary. If you need this kind of accuracy it will be for designing and testing DCC equipment and you will already have a bench scope to hand. As DCC users we can just measure the DC output from a decoder with a £50 MM and add 5-10% to get the track voltage. A £2.50 meter in my case (or £9 for my "expensive" analogue one). Yes, I have used "semi posh" £50 meters, and in my time had access to seriously accurate measuring kit, but for most model railway use, a cheap meter will do all you need. Who really cares if track voltage is 12.5v or 13.5v, so long as it is consistent over a layout ? Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 I said £50 because I'll only ever recommend CATIII 300V meters to people. Whatever it was originally bought for, it will inevitably be poked around in mains at some point, and if someone gets fried I don't want it to be my fault! Link to post Share on other sites More sharing options...
250BOB Posted January 26, 2014 Author Share Posted January 26, 2014 Hi Guys Here is the Multimeter I have, remember I did say its pretty old.......15 yrs or so. Link to post Share on other sites More sharing options...
ZiderHead Posted January 26, 2014 Share Posted January 26, 2014 Hi Guys Here is the Multimeter I have, remember I did say its pretty old.......15 yrs or so. 25 Jan 2014 002.jpg OK that looks fine for testing. Some uses: V⎓ (DC voltage) 20V range: Measure the voltage across a decoder function output. This is the voltage being supplied for lighting circuits, smoke generators and anything else connected to function outputs. Add 5-10% and this is your DCC track voltage. Measure the voltage across the decoder motor output at highest speed step. This is what the motor is getting. Some decoders allow you to set the motor voltage lower than the decoder voltage using a CV, so you can check this too. Ω (resistance) 200Ω range: Use this for continuity testing wiring, track joins etc. and for finding shorts where they shouldn't be. A good connection will be 0Ω to a few Ω at most, the lower the better. If it displays 0L it means there is no connection. If it flashes between the two when you wiggle the join around it means its intermittent (you don't want this) and you need to fix it. Diode (next to hFE): Use this to check which way round LEDs should be connected. It will show some voltage if the LED + and - are connected to the meter + and -. It will show 0L if the LED is connected the wrong way round. If it shows 0L connected both ways - your LED is blown! Link to post Share on other sites More sharing options...
Simon G Posted January 27, 2014 Share Posted January 27, 2014 I have an older digital mutimeter originally bought from Tandy, with similar ranges and facilities to 250BOB's. I wouldnt be without it. It has enabled me to solve problems on locos, track & controllers countless times. Once you start using yours, you will wonder how you ever managed without one. Link to post Share on other sites More sharing options...
250BOB Posted January 28, 2014 Author Share Posted January 28, 2014 Thanks for all your help as ever guys............. Much appreciated Bob. Link to post Share on other sites More sharing options...
Brian Posted January 29, 2014 Share Posted January 29, 2014 Hi You can also use the ac voltage range (200V ac on the meter shown) on DCC powered items. While the reading obtained wont be accurate it will be an indication of voltage arriving at the test place. Plus whatever is read at the input connection should be the same reading virtually all around the layout give or take a little bit of leeway! Reading a similar reading around the bus or rails proves all is good even if not 100% accurate. A noticeable swing in volts anywhere shows a problem occurring which needs to be resolved! Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted January 29, 2014 Share Posted January 29, 2014 That's how I use mine with respect to the DCC output, simply as a comparator. The absolute value isn't what matters for almost all on track DCC trouble shooting, just consistency. If I ever do find myself in the deep and sticky, I will have to run up to Yorkshire to get my Cossor storage scope (which is on permanent loan to my Dad, since he is the electronics hobbyist in the family). Link to post Share on other sites More sharing options...
ZiderHead Posted January 29, 2014 Share Posted January 29, 2014 MMs cant read DCC track voltage (see above) so dont bother to try and use that to check track/bus wiring. They can however measure DC voltage and resistance very accurately, so use this to test track/bus. Either: Disconnect all DCC from layout, connect a DC supply (controller, battery) and measure V at points around the track/bus. Or, simpler: Disconnect all DCC from layout, connect the layout + and - together and measure R at points around the track/bus. Link to post Share on other sites More sharing options...
Brian Posted January 30, 2014 Share Posted January 30, 2014 Sorry to disagree with you, but virtually any digital multimeter that's able to read ac volts can be used on DCC to read a voltage. The voltage read won't be the accurate voltage unless a true reading meter is used, but it will be a darn good indication of the supply volts being available and once read the same reading should be obtained around all the DCC powered rails. Its a good guide as confirmed by 34...... In post 24 after my original reply. Edit to add 'digital'. Link to post Share on other sites More sharing options...
250BOB Posted January 30, 2014 Author Share Posted January 30, 2014 Following your guidance guys.....I took my MM and measured the voltage everywhere around my layout after the addition of several extra droppers which have been fitted. The reading was a constant 16.2v Bob Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.