RRampMeter Application Notes

RRampMeter
Updated App Notes in PDF file (1.26 MB)
Don's Application Notes
Combined document - RR Updated App Notes and Don's App Notes (1.58 MB)

· As a result of my involvement in "Command Control" Systems for 16 years, it became apparent that Model Railroaders needed a simple to use, accurate tool to measure volts and amps for their Railroads. The advent of DCC with its unconventional waveform further amplified the need. I conveyed the concept and format to Larry Maier, a Model Railroader, and Electrical Engineer who is also a vital contributor to our DCC development efforts. His resulting design speaks for itself. Jim Scorse from NCE Corp also made some great suggestions.

· The maximum DCC and DC voltage is approximately 23 volts (covers the complete specified NMRA voltage range). The maximum DCC and DC current is approximately 9.2 amps. The maximum AC voltage is about 17 volts while the maximum AC current is about 6.5 amps. AC signals have a higher ratio of the maximum signal value to the RMS signal value than does the DCC and DC signal. These values may vary slightly from unit to unit due to component tolerances. The accuracy is between 2%-3% full scale. Two status indicator LEDS indicate either DCC or AC voltage, no indication on LEDS means DC voltage is present. When measuring DCC and AC voltages and current, any polarity will work. When measuring DC voltage, proper polarity is necessary. If you attempt to measure a DC voltage and there is no readout, simply reverse the connection polarity and you will get the proper readout. Units with battery or an external DC power supply will display DC voltage and current irrespective of polarity.

· Version IV RRampmeterHP is same as III but designed for large scale high voltage and current applications with the following specs: DCC: 38.6 v and 18-20 Amps; AC: 27.6 v and 18-20 Amps; DC: 38.6 v and 18-20 Amps

· Owners of the RRampmeter Version (1) can upgrade to Version (2) or (3) by purchasing the following parts from Radio Shack.

Version (3) Upgrade
Item	Part#	Total Cost
9V Battery Snap Connectors	27-324	$1.99
Switch	275-409A	$1.99

To install the battery connector (see Fig 4), solder the red or the positive lead of the battery connector at the J3 location to the hole with the square pad. Solder the black wire to the hole with the round pad. Solder these connections to the back side of the board so that the battery connector will fit in the enclosure. To install the switch (see Fig 4), desolder the jumper, and solder the switch into the three holes marked S1 on the top side of the board.

· Amperage must be measured in series by connecting the left set of contacts or clip leads to the input power supply or power source while the right set of contacts or clip leads are connected to the load or isolated track section where current is to be measured (Fig 1). The RRampmeter may be connected in the reverse direction without damage, but the display will show the current used by the RRampmeter in addition to the load current (about 0.03 to 0.04 for no load) (Fig 4). The voltage display also will not account for any voltage drop in the RRampmeter itself.

· Voltage can be measured from the left or right set of contacts or clip leads. If measuring voltage only, then either end of the RRampmeter may be used accurately.

· We do not recommend soldering directly to the buss bars that connect the adjustable contacts as this may interfere with the operation of the adjustable contacts (Fig 2).

· For Panel or Fascia mounting, Version (1) can be used. You will have to cut out holes in your fascia for the LEDS and the Indicator Lights. Four mounting holes are provided on the circuit bd for mounting. You can also use Version (2) and mount the enclosure cover to your Fascia if you prefer a dressier appearance (Fig 3).

· The RRampmeter is designed to read true RMS voltage and current. The RMS values are proportional to the power being supplied to the layout. An average reading meter (most inexpensive meters found in electronic stores, hardware stores, etc.) WILL NOT agree with the RRampmeter. The RRampmeter is displaying the correct values.

· Some DC power supplies use pulsed power for low speed. The RRampmeter will read this signal at its correct RMS value, but will display the AC PRESENT light. Once the supply transitions to full DC, the RRampmeter will continue to display the correct values, but the DCC PRESENT and AC PRESENT lights will both be out.

· If the current display shows more than 0.00 amps when only the booster is connected to the left hand input, then the display value may be adjusted to 0.00 by turning R44 until the display just transitions from 0.01 to 0.00.

· When using a battery, the RRampmeter will not show 0.00 volts with no signal connected. This is because the open contacts on the input actually pick up some voltage from the surroundings (power lines, DCC on the tracks, etc.). In addition, the circuitry used cannot quite reach 0.00. The RRampmeter is calibrated to read correctly above several tenths of a volt.

· The RRampmeter will measure voltages down to approximately 7.00 volts without using the 9V battery option. For DCC, this is more than adequate. To measure lower voltages, the battery option must be used. If the battery is connected, one position of the switch will turn the RRampmeter on using the battery. The other position will disconnect the battery and allow the RRampmeter to be powered from the input voltage. Either position may be used with the battery connected.

· If the RRampmeter is operated at currents in excess of 5 amps on a continuous basis, then it must be mounted in such a way as to allow free air circulation for cooling.

· The RRampmeter is a great 9V battery tester. Just connect the battery across the track inputs.

· You may be surprised at how much booster voltage is lost in track feeders, long stretches of track, and control switches. The RRampmeter is telling the truth.

· The RRampmeter will work with common rail systems. If you want to measure the current in a single track block, connect the common rail feed to J1-1 (J4-1 or J6) and the remaining side of the booster to J1-2 (J4-2 or J7). A single output connection may be run from J2-1 (J5-2 or J9) to the desired block. If you want to measure the TOTAL current on the common rail feed, connect the common rail to J1-2 (J4-2 or J7) and the remaining side of the booster to J1-1 (J4-1 or J6). The common rail is then connected to J2-1 (J5-2 or J9).

· We have tried the RRampmeter in conjunction with the programming track with mixed results. In some cases, the current drawn by the RRampmeter to operate itself may be sufficient to upset the programming sequence. If you want to operate the RRampmeter with the programming track, it may be necessary to use the battery option.

· If you plan to use the RRampmeter without the case in a situation where it will be handled, it may be wise to glue Y1 and C1 to the printed wiring board to prevent an accidental component removal. We find that a touch of "Crazy Glue" or equivalent is ideal for this purpose.

· J4 and J5 are optional and sized for a two terminal header for use with a connector. The DigiKey part number is ED1817-ND. The mating plug is DigiKey part number ED1717-ND. You may also solder wires directly to these holes for a permanent installation.

· If you are installing the RRampmeter as a permanent fascia display, a piece of red clear plastic or lighting gel in front of the display will improve the contrast.

We welcome comments or suggestions from readers; please write or call.