I am looking for a DMM which can measure and display both DC voltage (average) and AC voltage (mV ripple) at the same time.
I have a handheld unit that does this but I really would like to get more of a bench style instrument. I recently bought a DM3058E based on the premise that this unit does this - but in reality it switches between the DC and AC measurement modes, causing the internal relays to cycle with each measurement. Because this is going to be a common measurement for me I'd rather find something which isn't going to wear out internal relays when in this mode.
I don't need a lot of accuracy/resolution. A plus would be support of ACV+Frequency and so on. And no, I don't want to just use my scope....
Any ideas?
Keithley 2001 can display DC, AC, and Frequency simultaneously. The update rate of the display is slowed down since the instrument needs to cycle through the different measurements each time. AC measurement can be set to DC coupled so that AC+DC true RMS is measured. Peak voltages can also be measured instead of RMS, and crest factor can be displayed. It is a very versatile meter. My 2001's are flat (+-0.1 dB) in AC to about 4 MHz and and -3 dB at 7 MHz. Very few meters have better AC bandwidth (only the venerable 3458A comes to mind).
The 2001 is an older design, no fancy color LCD, just a nice VFD. It is still available new, but is very costly (>$4000!!). It is common enough on the used market, but even used, it goes at a premium since it is a true 7.5 digit meter.
There is no reason not to use two different meters, one for DC and one for AC. In fact, this may be the best solution since it may give you better AC accuracy. Consider that the AC ripple is usually << the DC offset. If using a single meter, you can imagine that the meter will need to either change range when measuring the AC portion of the signal, or sacrifice accuracy and resolution by not changing range. The former will likely result in clacking relays, and the latter is entirely undesirable when AC << DC.