I am generating a pulse waveform which has a time period of between 150 - 250 us (it is not constant) and repeats every 4ms. I was trying to find a multimeter or oscilliscope that can give me the True RMS of this waveform but don't really know what I should be looking for. I have tried the ISO-TECH IDM66RT, the KEYSIGHT U1232A and the AMPROBE 37XR-A but all are giving different True RMS readings (For voltage and current). I believe it is because these are for Sinusoidal wave forms and are struggling with the pulse.

Is there a suitable multimeter or oscilliscope that could give me a reliable True RMS reading for Voltage and Current and what would I need to look for in a multimeter?

Thanks.