Mismatched parts

Thomas

You will need four of those Amp meters to measure four zones.  An Amp meter must be wired in series with the circuit it is measuring.  aka power source (DCC booster) -> amp meter -> one zone of the PSX4 -> layout.  Maybe it could be done with four  current sensors, like a NCE BD20, and a microprocessor.

Doug W

Measure one at a time

Sloppy, but you could set it up with 4 relays driven by a 4 step counter that sequentially cycles through each zone. Display zone 1 for 10 seconds, zone 2 for 10 seconds, etc. A LED for each zone would indicate which zone is currently being displayed.

This is a decade counter for a traffic light but is essentially the circuit you would need for the relay cycling.

[EDIT] Use MBB type relays to avoid power cycling the decoders, a valid problem mentioned in later comments. 

Will Not Work

  There are a number of issues with your plan:

• Rotary Switch - The contacts have to be able to handle the full power of the Power District Load, and the switch will break between contacts - Your trains will stop for that instant.  Cutting off power and switching it back on under load is not a good thing.
• RRampMeter - This must be cut into the power district circuit in 'series'.
• Power Flow - This is relative, the DCC signal is a square wave AC signal.

  The 'Real' Solution is to have 4 RRampMeter's(one for each power district.  Why do you feel you need this level of control?  Also, the diodes are not needed as this is not a DC output.

  Here is how the RRampMeter should be cut into the circuit:

  My understanding is that you want ot cut this rotary switch in between the output of the RRAmpMeter and the power district.  You will need additional contacts to keep the power flowing to the other 3 power districts.  Using your rotary switch(6 position, 2 poles), you will be dropping power as you rotate between power districts.  If you do not blow something(like a $100 sound decoder), you most likely cause your sound decoders to do a power on Start Up cycle.  I understand that you do not want to spend $70 for each power district, but buying a large multi-deck rotary with sufficient power capacity is not cheap either...

Jim Bernier

Switching Problems

The primary problem with switching the inputs and outputs, is that you must break one set of contacts (inputs and outputs for one channel) before connection to the next set. That means that that if you are running you will momentarily kill the power on two blocks while switching. Now if you (and everything connected to the blocks) do not mind the power cycling, no problem. However, I suspect that you were hoping that you could get the switch to work and continue to operate. Not happening with a mechanical switch and the RR Ampmeter.

Here is how I did this with one RRAMP Meter ..................

..........and 3 PSX breakers, one being a reversing section.

If you read the instructions from the maker* you will see you can use a toggle switch to manually turn on a breaker that is tripped.  Another toggle will also turn on or off the district it handles.** I have my RRamp Meter connected between the output of my DCC command station booster and the bus that feeds the input on the PSX's.  It reads everything that is on.  If for some reason I want to check a single district, I just turn off the other 2 and it is now reading the only one on.  That might piss off the guys who are running in the other districts but as I'm 90% a one man band, it's not a problem.  If you are looking at diagnostics this is an OK system.  If you want to monitor each section, I think you'll have to get a meter per section.

*http://www.dccspecialties.com/products/pdf/man_psx1.pdf

**as well as how to connect remote LEDs for power on (green)  and shorts (red)

Peter

Thanks so far, plus additional question and info.

Great responses so far, thank you everyone. Now let me add one more caveat that I was thinking of and did not write in my original query.

SIMPLES WAY

 Buy 4 Current transducer, 1 for each circuit and a digital amp meter. Run the output leads from the transducers to your selector switch and the common of the switch to the digital amp meter. This way you are NOT breaking the Base station output to each block and can ck the current draw of anyone circuit. Call a local elctronics distributor and he can set this up for you. Very easy to do. you will need to match the transducers to the amp meter.

As an example:

http://www.crmagnetics.com/Products/CR8410-P93.aspx

http://www.crmagnetics.com/Support/Technical-Reference/ctl/details/itemid/0/mid/372/instrument-transformers-application-guide

@CarterM999.................

I must be missing something.  I looked up those web pages and realized there were way too many to select from.  Any idea which one (part #) to use?  Are you aware that three of the current transducers I looked up were around  $180.00?   A Rramp meter is only $60.  Help us out here, thanks.................

Peter

 I have no idea which model

I have no idea which model CT you are looking at but here is an inexpensive model CT from Amazon. Not that this is the exact one needed but close, you will need to match the CT with a specific meter. $8.00 free shipping. I retired 15 years ago and like all fields the products/engineering has changed significantly. Cking with the distributor is best for matching meters to CTs for your specific application.

Carter

http://www.amazon.com/Professional-Precision-Current-Transformer-Ta17l-04/dp/B00NASW8Z4/ref=sr_1_1?s=industrial&ie=UTF8&qid=1426415982&sr=1-1&keywords=current+transformer+Model+17-2000

 Mouser Electronics has a

Mouser Electronics has a wide selection of Meters with CTs.

http://www.mouser.com/Search/Refine.aspx?FS=TRUE&N=4294759241+254579+1323043

Will it work?

The measuring point is after the boosters. There will be square wave AC current. Is just a coil and meter going to work correctly?

@CarterM999.................

Here where I'm lost about using these transducers.  The current the Rramp meter is reading is really a combination of AC and DC. 

This from WIKI: The voltage to the track is a bipolar DC signal. This results in a form of alternating current, but the DCC signal does not follow a sine wave. Instead, the command station quickly switches the direction of the DC voltage, resulting in a modulated pulse wave. The length of time the voltage is applied in each direction provides the method for encoding data.

To represent a binary one, the time is short (nominally 58µs for a half cycle), while a zero is represented by a longer period (nominally at least 100µs for a half cycle).

The reason DCC Specialties (http://www.dccspecialties.com/products/rrampmeter.htm) invented the Rramp meter in the first place was to convert this combined signal into something that their meter shows in Amps and Volts.  For the same reason that a normal Ammeter cannot accurately read DCC current I'm wondering if these transducers can.  Not knowing how they work makes it hard for me to understand.  If I have it right, they measure the current flowing through the wire they are next to/around and sent it to a meter meaning you don't have to run the current carrying wire through the meter, is that right?  As they come in AC or DC varieties I thsink the same problem a regular meter has reading a DCC current will exist. 

At 8 bucks a pop it certainly seems worth investigating further as a cheaper alternative to 4 $60 Rramp meter.

Thanks..............

Peter

tic field  Transducers work

Transducers work on the magnetic field surrounding the current carrying wire. AC and DC currents produce this magnetic field. The magnetic field of an AC curent reverses that is it goes from "0" to max back to "0" to - max back to "0" in 1/60 of a second thus 60 Hz or cycles. The field reaches it zenith collapses to 0 back to zenith and collapses 60 times per second. The transducers convert this magnetic field into a current with a voltage and thus is able to be read by a voltmeter, the Root Mean Sq of the voltage, and convert it to a reading we understand, i.e. 120 volts, 240 volts etc etc.

The voltmeter voltage shown is V/RMS, aprox. 70% of the RMS voltage.

Formula: V

= voltage

V/m = meter voltage

V/rms = volts at Root Means Sq.

Maybe a little deep for some...especially if you have your own opinion on the Power Laws of Physics.

Keep in mind that Power is measured in Watts.

The term “RMS” stands for “Root-Mean-Squared”. Most books define this as the “amount of AC power that produces the same heating effect as an equivalent DC power”, or something similar along these lines, but an RMS value is more than just that. The RMS value is the square root of the mean (average) value of the squared function of the instantaneous values. The symbols used for defining an RMS value are V_RMS or I_RMS.

The term RMS, ONLY refers to time-varying sinusoidal voltages, currents or complex waveforms were the magnitude of the waveform changes over time and is not used in DC circuit analysis or calculations were the magnitude is always constant. When used to compare the equivalent RMS voltage value of an alternating sinusoidal waveform that supplies the same electrical power to a given load as an equivalent DC circuit, the RMS value is called the “effective value” and is generally presented as: V_eff or I_eff.

In other words, the effective value is an equivalent DC value which tells you how many volts or amps of DC that a time-varying sinusoidal waveform is equal to in terms of its ability to produce the same power. For example, the domestic mains supply in the United Kingdom is 240Vac. This value is assumed to indicate an effective value of “240 Volts RMS”. This means then that the sinusoidal RMS voltage from the wall sockets of a UK home is capable of producing the same average positive power as 240 volts of steady DC voltage as shown in the formula above.

Perhaps an interdiction here by Bruce may shed some light on the situation...an article covering Transducers and ampmeters in DCC would be of interest.

@CarterM999.................

Wow, lost me there.  As my long time friend and Amtrak co-worker who ran the electronics/radio shop at Amtrak would say when I asked him how does that thing work, "It's magic, and the smoke we see when we short out that thing is the magic escaping!"  Worked for me..................

My question is, based on what DCC "current" is, will a transducer read it correctly?

Peter

AC Transducer

Hi Peter,

I always think of an AC transducer as a step-down transformer with the wire going through the center as the primary and the two-wire output as the secondary.  That transducer works very well on an AC sine wave input, but I don’t think it will faithfully reproduce a PWM DC signal that swings plus to minus.  The sine wave AC voltage is a gradual waveform that goes from zero to peak and then gradually back to zero. 

The ideal DCC signal is a voltage that will rocket launch to peak, stays at peak a “while” and then nosedives from the peak (like a square wave).   Both waveforms go from peak through zero and then to a negative peak, and repeats.   I don’t have a transducer on hand to hook to my oscilloscope for verification.

Carter999 gives a very good explanation of AC(rms) current for a sine wave (one of the better ones I have read), but the equation will not work for non-sine-wave DCC.

We used to call the internal workings of an electronic board FM.  “Fancy Magic” for those of you that may have something else in mind.  The smoke was an “error signal”.

Gene

Gene, thanks for your input.............

I don't pretend to understand exactly how electronics work, hence I was OK with the magic and smoke analogy.  But logic tells me that whatever DCC specialties does inside their magic box (Rrampmeter) to read the odd current of DCC and converting it to Amps and Volts we are used to, so must the transducer to get the correct volts and amps reading, right? I'll bet such an animal does not exist for if it did, I'm sure we'd know about it through a forum or from a manufacturer like Tam Valley or Iowa Scaled.

Peter

will a transducer read it correctly?

First a Note: A complicated and or expensive device (eg. Hall effect) is not needed to sense DCC currents (but they can be fun to design with). A simple precision resistor in the 0.01 Ohm to 0.10 Ohm range will work just fine as a current (to voltage – IAmps = VVolts / ROhms) sensor / transducer (Basically what is used in RRAmpmeters).

For DCC currents the short answer is: No! You can not simply hookup a current sensor (current transformer, Hall effect, resistor based etc.) to most off the shelf meters and get an accurate (or understandable RMS, Average, Peak) reading. You can detect that there is a current in the circuit, but you may not be able to determine much useful information from the readings. If you get a high reading, depending upon the transducer and meter used, your block is probably drawing a high current (but maybe not). Or you could read under a hundred milliamps, but the peak current (which could indicate a frying a decoder) could be just below (or in some cases above) the rating of your circuit breaker.

The longer answer: Current sensors can be used with some meters (not your typical digital meter) to measure non-sinusoidal current waveforms (I usually rely on an oscilloscope), or they can be incorporated in meters specially designed for the purpose like the RRAmpmeters. A multi channel measurement DCC measurement system could be assembled from a uPC board (Arduino), some precisions resistors for current sensing, an LCD display, a power supply and a few other components. The uPC could be programmed to measure and display voltage and current characteristics (Peak and RMS Voltage and Current and more), for each channel. Interesting ideal, but I think I actually designed something like that a few years ago (or was it a student project?). Have to check the pile (I mean file).

Good thought even a nice try.

Like Thomas, the OP, I've mulled the same notion with my four power zones.  I've aborted the switch/rotary notion having stumbled through many of the thoughts and challenges mentioned in the thread.  

I'm going to see what my digital clamp on current probe reads.  I think the simplest approach remains buying additional RRamp meters, one for each PSX if a  fellow is really that curious.

Joe

DCC amp meter

This will only measure current I have built two. One for home and one for a club. Accurate. Cost about $10.00 with the Harbor Freight meter. Use the 20 ma scale. I bought the PC board and parts from him. Meter from Harbor Freight.
I used the 2010 circuit. I enjoy DIY.

http://home.cogeco.ca/~rpaisley4/DCCammeter10.html#PCB

He use to show the meter at one time.

Rich

Amprobe vs RRamp

My amprobe is admittedly very old, 15 years? It only reads about 20% of the current of the RRamp meter. Works, but my Amprobe model is not nearly sensitive enough for MRR work.  

Rich thanks for posting the link to the alternative current measuring method. I'd seen it before but the refresher was  allgood.  This thread has only reminded me of how good a bargain the RRamp meter is.  

Have a great day!

Joe