When do I need to use a “True RMS” multimeter?

If you are dealing with systems like LED lighting, fluorescent lighting or special control systems like 2-wire irrigation, you will probably need a True RMS multi-meter for testing and troubleshooting.  This is because the AC signals are variable and need the advanced meters to accurately measure them. As long as you are aware that the readings may be off in some cases, you can use a regular, average-responding RMS multi-meter. See our application note on True RMS.