Extech EX330 multimeter - temperature probe

[Hobby73]

I work with low power DC circuits and I'm looking for an inexpensive (< $75) multimeter that measures both low current (microamps range) and temperature.  I want to use the thermocouple probe to measure heat on components stressed by power at or above their ratings.  I don't need excruciating accuracy on temp measurements, within +/- 5% is good enough for my purposes.

The EX330 looks perfect!  It has many favorable reviews.  However, I read a couple online reviews where the users said the temp sensor is "useless", but never elaborated about why they have this criticism.  Is there some glaring problem everyone else knows that I'm missing?  I don't want to place an order for this unit if the temp probe is truly useless.

[mos6502]

The accuracy shouldn't be an issue. What I'd be more worried about is that the insulation is bare fiberglass. Every time you touch it, your hands will itch. And you will get tiny glass fibers on everything.

The cheapest meter that comes with a decent probe is probably the Digitek DT-4000ZC (only does celsius though) or the DT-2843.

But really, do yourself a favor and at least get a Fluke 17B+.

[Hobby73]

Regarding the Digiteks/Tekpower, they won't work for my needs because I want temp in Celsius or Fahrenheit.  And this brand is not widely available in the US so I am doubtful about support here, as well.

I would love to get the Fluke 17B+, it was actually on my short list!  The problem is that warranty service is only available in China and India, not in the US where I am located.  I was struggling with taking a risk because I know the probability of needing repair service is very low.  But if I did need service, I would be SOL.  I'm still thinking about it.

Very interesting comment you made on the fiberglass.  It seems the Type K thermocouples on this class of multimeters commonly have fiberglass insulation.  I didn't realize the problem you describe.  I suppose I could wear nitrile gloves when using it ... I am always using them for cleaning and such tasks. 

Can I purchase a different/better thermocouple that is compatible?  If not fiberglass, what is the preferred insulation for these thermocouple probes?

[RobertoLG]

my Digitek DT-2843 R, has both Celsius and Fahrenheit, just press select to change from one to the other

[mos6502]

Service? What service? The Digiteks are $40 Hung Wei Lo meters. But so is the Extech. You could buy the Fluke thermocouple. But it's like $20. If you add that to the price of the Extech, you might as well buy the Fluke. Of all the meters discussed, the Fluke has by far superior construction and quality. It's extremely unlikely to have a problem. It also comes with the superior Fluke TL75 probes. This is really a no-brainer.

[Hobby73]

I looked up the thermocouple that comes bundled with the Fluke 17B+.  It's a Fluke 80BK-A temperature probe and costs nearly as much as the EX330 multimeter!  I guess the probe itself is very important to the accuracy of temp measurements. That's likely a key part of the value you get with the Fluke 17B+.

Update: I just checked the price again on the Fluke thermocouple and while it's priced around $40 in retail stores, it's MUCH cheaper on eBay, only $10.  So either these eBay probes are fakes or the markup on this stuff is incredible. 

[Hobby73]

To close this off, I started out looking at the $50 Extech.  Then, on a quality basis, I moved up to the Fluke 17B+ for $120.  Finally, for just $20 more, I decided on the Fluke 116 which has similar capabilities as the Fluke 17B+ but offers a longer warranty period and US-based mfr support.  Order placed.  I'm done.  Geez, it was easier to choose a new car.

[Hobby73]

UPDATE:  I just read this other thread indicating the Fluke 116 (the model I ordered) uses a high impedance architecture that makes it poorly suited for my low power electronics testing.  It's more of a specialty meter for HVAC.  ( post: https://www.eevblog.com/forum/beginners/fluke-116-has-no-fuses!/msg305709/#msg305709 )

After all that, I ordered the wrong meter!  I was fortunate that I was able to canx the order before it shipped.

Back to look at the Fluke 17B+.

[Hobby73]

Just found this additional post about the Fluke 116, so I'm not the only one caught by surprise.  I don't fully understand the issue about high impedance, but apparently it has problems working with a reference tester for low current measurements. 

https://www.eevblog.com/forum/testgear/fluke-116-ua-troubleshoot/msg316710/#msg316710

[mos6502]

Just found this additional post about the Fluke 116, so I'm not the only one caught by surprise.  I don't fully understand the issue about high impedance, but apparently it has problems working with a voltage reference unit. 

https://www.eevblog.com/forum/testgear/fluke-116-ua-troubleshoot/msg316710/#msg316710

The 116 doesn't have current measurement capability per se. It has a microamp range with a fairly high resistance that's really only designed for testing flame sensors in HVAC. The 117 has an amp range, but no microamps. The 11x series are mostly designed for HVAC and electricians. For general electronics, you'll be way better off with the 17B+.

[Rascal]

My EX330 is right on the limit of its accuracy - Im not impressed with it at all. I have other far cheaper Chinese meters that are far more accurate. You don't always get what you pay for

Paul

[Hobby73]

My EX330 is right on the limit of its accuracy - I'm not impressed with it at all. I have other far cheaper Chinese meters that are far more accurate. You don't always get what you pay for

Paul

Paul, did you check inside the unit to see if the adjusting pot is accessible for calibration?  I'm starting to wonder if it really matters very much about DMM accuracy drifting if it is easy to adjust.

UPDATE:  I just found this post for EX330 calibration:

https://www.eevblog.com/forum/testgear/calibration-of-extech-ex330/msg763125/#msg763125

[Hobby73]

The 116 doesn't have current measurement capability per se. It has a microamp range with a fairly high resistance that's really only designed for testing flame sensors in HVAC...

What should I have looked at in the Fluke 116 specs that would have told me this?  I don't want to make this mistake again. (Data Sheet attached).  I don't see anything that suggests is is not suitable to measure low current for general electronics.

[Wytnucls]

If you only need a 600uA DC/AC range with 500Hz bandwidth, that meter is fine. Be aware that the AC uA range is DC coupled only.

[mos6502]

If you only need a 600uA DC/AC range with 500Hz bandwidth, that meter is fine.

Except for the massive burden voltage: https://www.eevblog.com/forum/testgear/fluke-116-ua-troubleshoot/

As I said, not really intended for electronics ...

[Hobby73]

When I check the specs for Brymen DMM's (as well as their derivative brands Amprobe & Greenlee), they plainly state the burden voltage.  Fluke does not (at least for the 116). 

[Wytnucls]

If the uA range burden voltage is really that high (3x UT-61E), it would indeed be cumbersome to use with low voltage circuits. Fluke should have warned potential users, at least in the manual.

[Hobby73]

... For general electronics, you'll be way better off with the 17B+.

Any chance that you might know the Burden Voltage for the Fluke 17B+ for its various current ranges? 

I checked the data sheet and user manual I found online and it's not indicated in either of those docs.  I also contacted Fluke support here in the U.S. and they said they don't offer this model in North America (I already knew that) but they checked the resources available to them and the Voltage Burden is not specified for this model.  I find that very odd, especially for a feature-packed unit like the 17B+ with its uA current ranges. 

Not sure what to make of this glaring omission unless the mfg is not disclosing specs that may appear unfavorable to prospective customers. Maybe that's too harsh, maybe not?

[XFDDesign]

I own two EX330s as I'm using them for the basis of developing a 200 level circuits class.

As your question is in regards to the thermocouple, my experience with it is that it isn't just "on edge" of accuracy, but that it's downright erroneous. The meter presents a questionable answer below 45F (it seems to plateau at around 35F), and as it goes hotter, it might be +/- 3-5 degrees F. What is funny is that I move the exact same probe to my Fluke 179, and I get different, repeatable, and accurate results.

The EX330 is fine for a probes on a voltage reality check, but it isn't something I'd recommend using for any amount of precision.

[Hobby73]

I own two EX330s as I'm using them for the basis of developing a 200 level circuits class.

As your question is in regards to the thermocouple, my experience with it is that it isn't just "on edge" of accuracy, but that it's downright erroneous. The meter presents a questionable answer below 45F (it seems to plateau at around 35F), and as it goes hotter, it might be +/- 3-5 degrees F. What is funny is that I move the exact same probe to my Fluke 179, and I get different, repeatable, and accurate results.

The EX330 is fine for a probes on a voltage reality check, but it isn't something I'd recommend using for any amount of precision.

You confirmed what I read about the temp measurement for this unit.  Much appreciated!

[SeanB]

So the cold junction compensation is either a fixed offset or the compensation is not exactly in accordance with the thermocouple voltage. Hard to fix in either case, unless the compensation has both a zero and a gain control you can use to linearise it.  Simplest test is to put it in temperature mode and short the TC inputs with a copper wire, and cycle the unit from cold ( in a fridge) to around 40C using a warm oven, and see if the cold junction temperature on the display matches the actual temperature.