For starters, I'm no whiz when it comes to electronics. I know just enough to get by. I have a DCC layout. I had a section of track that I suspected might not be getting enough juice so I got out my analog Multi-Meter and began testing the section I suspected had a problem as well as the sections on either side of the rail joiners for that section. I seemed to be getting a strong current everywhere, then suddenly there seemed to be a significant drop. I went back to check the sections I had just tested and they too showed a weak current. Then I discovered something curious. The strength of the signal changed significantly when I switched the red and black prongs on the Multi-Meter. When I touched the red prong to the inside rail and the black to the one closest to the aisle, I got a very strong signal. When I reversed them, the signal dropped to about a quarter of what it had been. I never knew that it mattered which prong touched which track but apparently it does. I had always touched red to the inside track and black to the outside track because those are the colors of my bus wires. I switched them inadvertently during testing and saw a sharp drop off in the signal. Can somebody explain why it would matter?
Meter bad or a loose probe connection?
Just checked my NCE system and read about the same voltage both ways.
And if you are touching the rails you are reading voltage, not current.
A mulitmeter has 3 or 4 ports where you can connect the probes.
Randy could give a better explanation, but if the probes are in the proper port, ppolarity should not create different readings.
Henry
COB Potomac & Northern
Shenandoah Valley
What did you have the meter selector set at? It might be possible to get different readings if you had it set to DC. AC Volts will give you some indication of available DCC voltage across the rails but it would be best if you could apply a bit of a load at the same time.
I use a RR Amp meter and clip an 1156 automotive lamp to the test leads which puts a load on the rails. Open circuit voltage may not pinpoint a weak connection feeding the rails.
Good Luck, Ed
BigDaddy....if the probes are in the proper port, ppolarity should not create different readings.
Yes, when reading resistances. When reading voltages, however, you can get the inverse voltage with the probes reversed but it's the same voltage only with a negative sign; not an entirely different reading.
[Edit: My comment above was made in regard to a digital meter. An analog meter does behave differently when the probes are reversed.]
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
John-NYBWI got out my analog Multi-Meter.
Nevermind.
-Kevin
Living the dream.
I agree, digital is the way to go. However, whatever the meter, set it to measure AC and in the 20 volt range. You want to see, with about 0.4 volt variance over passing seconds, about 13-14 volts showing.
If the rails are connected and being fed properly along their lengths, the voltage will be rather constant and robust, up near 13.5 - 14 volts. If you get drops, it could be a bad connection at a joiner. It could also be a damaged lead wire anywhere from the probe back to the connector.
make sure the probes have good contact. they can be affected by dirty rail
greg - Philadelphia & Reading / Reading
maxman Meter bad or a loose probe connection?
If either of those were the case, I would think it would show up no matter which way the probes were set.
Let me be clear. The change in reading occurred whenever I reversed the probes. It showed a strong reading every time I put the red probe on the inside rail and a weak reading every time I put the black probe on the inside rail. That's not the result of a loose probe or a defective meter. Tom's response seems to be the one that makes the most sense. I will also use settings selector has suggested and see what I get.
I am wondering if this is just an artifact of the anolog meter. I have little experience with the analog meters, but from what I remember you had to make sure you had the polarity correct. They can't just show negative voltage like the digital ones do. (This may have just been an issue with the one I used 20 years ago.) However, given Kevin's comment that the digital are easier to use, I think that was a common thing.
hgodling I have little experience with the analog meters, but from what I remember you had to make sure you had the polarity correct.
I deleted my previous, factual, and helpful replies.
As usual, Mike has pointed out that I was wrong about everything, sorry guys.
Happy Thanksgiving everyone. Enjoy you newly SPIKED thread.
I am out.
Change the battery.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
The lower end Analog meters can introduce meter loading just to make it interesting. The real low end ones can be 1k-Ohm/Volt, where a DMM will often be in the range of 1M-Ohm/volt. Your typical Fluke DMM is 1MOhm, a few are 10Mohm/V.
Even the pressure on the probes can make a difference between a good connection or not when taking reading. Especially important when measuring resistance. With analog meters a fresh battery can help, they usually don't have an indication for that on the meter face when measuring resistance.
John-NYBWIf either of those were the case, I would think it would show up no matter which way the probes were set.
what were the measurements? AC/DC?
Lastspikemike Is this a Digitrax DCC system?
Is this a Digitrax DCC system?
No, Lenz
I have 3 ways to check my DCC track voltage.
1. Analog Voltmeter: For this purpose, I use a Radio Shack multimeter dialed to AC voltage. My best guess from the position of the dial is approximately 12.5 volts. I get the same result with the same dial position no matter which way I place the two probes on the rails.
2. Digital Voltmeter: For this purpose, I use a Gardner-Bender multimeter dialed to AC voltage. The readout shows 12.4 volts with the probes placed on the rails one way and -12.4 volts with the probes placed on the rails the opposite way.
3. RRampMeter: The measurement shows 13.5 volts which I believe to be the most accurate measure of DCC voltage. If you operate in DCC, you should own a RRampMeter.
Rich
Alton Junction
gregc John-NYBW If either of those were the case, I would think it would show up no matter which way the probes were set. what were the measurements? AC/DC?
John-NYBW If either of those were the case, I would think it would show up no matter which way the probes were set.
i do mean the actual voltages being measured as well as whether AC or DC?
DC may be different. can't see how AC measurements can be?
Lastspikemike I just wondered if your analog multi meter is reading voltage delivered for address 0000 which would be a biased PWM simulated DC power. If these DCC systems with DC power available at address 0 then maybe a multi meter set to measure DC might pick up and display that voltage which would be much higher when measured one way than when measured the other.
I just wondered if your analog multi meter is reading voltage delivered for address 0000 which would be a biased PWM simulated DC power. If these DCC systems with DC power available at address 0 then maybe a multi meter set to measure DC might pick up and display that voltage which would be much higher when measured one way than when measured the other.
Nope .... not even close. Investigate zero-stretching ....
https://dccwiki.com/Zero_Stretching
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Lastspikemike John-NYBW Lastspikemike Is this a Digitrax DCC system? No, Lenz I just wondered if your analog multi meter is reading voltage delivered for address 0000 which would be a biased PWM simulated DC power. If these DCC systems with DC power available at address 0 then maybe a multi meter set to measure DC might pick up and display that voltage which would be much higher when measured one way than when measured the other.
John-NYBW Lastspikemike Is this a Digitrax DCC system? No, Lenz
Interesting. I was testing a second hand DC loco I picked up using address 0000. I wanted to see if it was working prior to installing a decoder. I can only do that with the main LH100 tethered throttle because my wireless throttles don't allow me to enter address 0000. I don't think I had left it on address 0000 when I was testing the track power but it's a possibility.
This morning I have been working out some wiring bugs for my Atlas switch control boxes and other accessories. I have the various panels daisy chained together using a Miniatronics 12V DC power supply. Some of the remote panels were not working. In testing the voltage at various points, I discovered that polarity mattered on those when I checked them with my Multi-Meter, so what you are saying makes sense.
Lastspikemike I read that some time ago. The net result is delivery of the mostly one way current the DC motor requires. That seems indistinguishable for practical purposes from a real DC current. After all that's how PWM delivers the correct power at a full twelve volts DC. I don't see the square wave DCC power delivery as different from the sine wave delivery of DC in this situation. After all the DCC square wave is actually a sum of a large number of different sine waves. DCC digital signal still has to be a wave, with a rise and fall. If you wish to explain where I'm mistaken that would be fine by me. Just referring me to the source you have doesn't do that, or at least I don't see where it does.
I read that some time ago. The net result is delivery of the mostly one way current the DC motor requires. That seems indistinguishable for practical purposes from a real DC current. After all that's how PWM delivers the correct power at a full twelve volts DC. I don't see the square wave DCC power delivery as different from the sine wave delivery of DC in this situation. After all the DCC square wave is actually a sum of a large number of different sine waves. DCC digital signal still has to be a wave, with a rise and fall.
If you wish to explain where I'm mistaken that would be fine by me. Just referring me to the source you have doesn't do that, or at least I don't see where it does.
Maybe check this out ? ....
https://dccwiki.com/Pulse_Width_Modulation
DC voltage is not used to control the motor. For that matter, there is no Straight DC voltage outputs on a decoder. Even the function outputs utilize PWM operation as well. Dimming a light on a decoder doesn't reduce the DC voltage (there isn't any) it reduces the pulse width, creating less on time so the light "appears" to be dimmer.
John-NYBWInteresting. I was testing a second hand DC loco I picked up using address 0000. I wanted to see if it was working prior to installing a decoder. I can only do that with the main LH100 tethered throttle because my wireless throttles don't allow me to enter address 0000. I don't think I had left it on address 0000 when I was testing the track power but it's a possibility.
Generally speaking, when using DCC and running a locomotive on a throttle, when you select another loco, if you don't stop the first one before releasing it it keeps going. In other words, if you did not make sure address 0 was set to stopped, even if it's no longer selected on the throttle the command station may be doing the 'zero stretching' to run a DC loco. That was probably the source of your different readings.
LastspikemikeIt seems to me that you measure voltage from each rail to a pseudo ground rather than across the rails as you would would DC power.
It's not a "pseudo ground", it's the system ground.
LastspikemikeYour analog multimeter really can't measure anything between the rails because the signal your multi meter is getting isn't a voltage signal per se.
I don't quite know what you mean by this but there certainly is a voltage between the rails that can be read by an analog multimeter. It won't likely be accurate because the meter is most likely measring the average votage and is calibrated for a sine wave but is trying to measure a square wave (RMS (root mean square) is what you really want and a RMS meter will be correct).
Measuring DC from each rail to ground and adding them together will give you an accurate voltage because the meter won't be callibrated for a sine wave, but that's not real easy to do around the layout unless you run a ground a round the layout. Measuring between the rails will give you a higher reading, but it's consistantly higher and can still be used to test for voltage drop.
LastspikemikeI read that some time ago. The net result is delivery of the mostly one way current the DC motor requires. That seems indistinguishable for practical purposes from a real DC current. After all that's how PWM delivers the correct power at a full twelve volts DC. I don't see the square wave DCC power delivery as different from the sine wave delivery of DC in this situation. After all the DCC square wave is actually a sum of a large number of different sine waves. DCC digital signal still has to be a wave, with a rise and fall. If you wish to explain where I'm mistaken that would be fine by me. Just referring me to the source you have doesn't do that, or at least I don't see where it does.
PWM motor control switches between 0 and +V, unless the motor is running in reverse where it switches from 0 to -V, but under normal circumstances it never constantly switches between +V and -V. DCC pulses constantly switch between +V and -V and are never at 0V, except for the moment it crosses from one to the other - definitely not the same as PWM.
With motors, it is all about the direction of current flow (Fleming's Law).
With PWM, it is the On/Off sequence that determines direction: In one direction the motor turns CW, reverse the sequence and the motor turns CCW.
The same thing works with Zero Stretching: Under normal circumstances the On/Off sequence on the rails won't develop much torque in a motor (or analog meter). By holding one rail On for a longer period, the current flows long enough to produce torque in the motor. The longer the period, the more torque and the motor spins faster. Direction is determined by which rail is held On for the longer period.
betamaxWith PWM, it is the On/Off sequence that determines direction: In one direction the motor turns CW, reverse the sequence and the motor turns CCW.
the period that it is on determines the effective average voltage
reversing the polarity affects the direction, not the sequence
As I said in the OP, I know just enough about electronics to get by (barely). You guys are up in the stratosphere now.
John-NYBW As I said in the OP, I know just enough about electronics to get by (barely). You guys are up in the stratosphere now.
LastspikemikeYou don't see the similarity. PWM sends a speed signal to the DC motor combined with the power to drive it. DCC does the same thing. The difference is only a power level signal is contained in the PWM "signal". I referred to the manner in which DCC current returns to the booster as a pseudo ground because that's what it is. That's why boosters that are connected together require a third wire. I may not understand the technical aspects of DCC but a I "know how it works".
I do see the similarities, but they also have major differences, the biggest being that the DCC voltage is constanly reversing and PWM is not.
Again, there is no "pseudo ground". The ground connected between boosters is just that, ground, the system ground, there is nothing "pseudo" about it.