DCC SPECIALTIES RRampMeter IV - MEASURES DCC/DC/AC VOLTS & AMPS "The Essential Tool" for Large G Scale Model Trains Hobbyists"
Accurately measures DCC, AC and DC Volts and Amps! DCC - 38.6 V, 18-20 A; DC - 38.6 V, 18-20 A; AC - 27.6 V, 18-20 A; PCB length 5.63"; Enclosure length
4", width 2", height 1.25" The amazing RRampMeter designed for Model Railroaders by DCC Specialties does what no other meter can do! Easy walk-
around measurements of layout voltage drops, accurate booster output setup to optimum voltages for decoders and sound units.
Measuring PWM Voltage - Manufacturer's Technical Response
The RRampmeter should accurately measure a PWM waveform. After all, DCC is a form of PWM. However, the RRampmeter reads the TOTAL RMS value of the waveform, DC + AC. Your Fluke set to read AC blocks DC and is only measuring the AC component. Since the lights and smoke unit are going to respond to the DC value of the PWM (and I assume the PWM is on/off, so there is a DC component), you should measure these outputs with the Fluke meter set to DC. One other thing to keep in mind is that the RRampmeter is designed to power itself from the input, so on a low power circuit such as a light output, the added load may affect the reading. Make sure you are using the battery for power and not the input signal. Even with the battery, the RRampmeter will load the circuit more than the Fluke (25.4K vs 10 Meg). For this reason, the Fluke set to read DC might be the better choice.