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Review of the EX330 DMM (Reviewed April, 2013), by Jack Ganssle
I'll present my Better Firmware Faster seminar in Melbourne, Australia February 20. All are invited. More info here.
You can't operate without a digital multimeter (DMM), but be prepared to write a big check for some units. I'd love to get one of Agilent's 34401A 6.5 digit beauties, for instance, but at $1100 it's more meter than I need or can justify.
There are a lot of inexpensive hand-held products (as well as expensive ones) available today. Extech has a variety of popular offerings. I recently acquired one of their EX330 models, which seems a robust, well-made unit.
Features include 4000 count LCD display, autoranging, the usual V, R, and A measurements, plus the ability to read capacitors, frequency and temperature with an included type-K temperature probe.
The unit has a non-contact voltage sensor; hold it against power mains and a light illuminates while the unit makes a strange squeaking sound. It works, to a point, when held right over 110 VAC outlets or switches, but I couldn't make it sense the wires through drywall. The manual does say one must hold the meter "very close" to the power source. So it's somewhat useful for seeing if an outlet has power without the associated risk of plugging meter leads into the outlet itself. This looks like a feature I'll never use.
I don't have a calibration lab so can't speak to its accuracy, though it matched my other instruments well. The devil is in the details; one must look at the specs closely. DC voltage is claimed to be accurate to 0.5% to 1.5% (depending on range) + 2 digits, which is pretty good for this class of device. AC voltage is about the same though the 2 digit error is replaced by 3 or 4 (except the 400 mV range which is 30 digits! I'm sure that's a misprint.) Temperature is 3% + 8 digits, plus unstated errors in the probe. Given that the resolution is 1 degree (F or C) that represents an awful lot of error. Update: checking it against my DMMCheck a year later, DC volts are within 2 mV, well withing spec, and resistance measurements are withing an astonishing 0.2%.
The autoranging works well except when trying to measure capacitors. One switch position covers caps, diodes and resistors, and in some cases when trying to autorange on a capacitor it never leaves ohms mode. With autoranging disabled it reads capacitors just fine. Update: After a year's use, I find the autorange hunts far too much and is quite annoying. I very much dislike that one setting covers ohms, diodes and capacitors; sometimes the unit will give a capacitance value when I'm measuring a resistor. Other times it seems confused and hunts between capacitance and resistance.
The autorange can be slow in resistance mode! Up to 4 seconds were needed at times, which doesn't sound like much but can seem an eternity when testing a lot of resistances.
The frequency measurements (0.001 Hz to 10 Mhz) are very fast. Just for fun I fed some non-sine waves in, and found it's perfectly happy with square waves, ramps, and even a cardiac signal! Pulses don't phase it at all; it gave accurate frequency measurements even on odd signals like a 5 MHz pulse 20 nsec wide. Duty cycle results were noisy on sine and square waves, and rather erratic on the admittedly-tough pulses.
The display's digits are big (1") and readable but really could use more contrast. There's a rubber case which should give it plenty of shock protection; DMMs can have a hard life.
At $58 (from Amazon) this is much cheaper than an equivalent Fluke. But it's not a Fluke, and won't light up your face with the delight one finds from working with the very best equipment. I find the Extech 330 to be an adequate DMM for most needs, and for digital people coping with some analog issues it's more DMM than you'll need. You can't beat the price. Update: You still can't beat the price. But the thing is quirky enough with the slow hunting that I get frustrated with it.