Fluke 77-IV vs ExTech EX330 differences I noticed. - Page 1
Forum section: electronics / testgear

author: blewisjr
author_rank: Frequent Contributor
timestamp: April 02, 2013, 12:59:16 pm
content: Yes I understand that these meters are in a totally different league. The Fluke 77-IV appears to have all the same functions minus the No Contact Mains voltage detector. The ExTech has mA, and uA but no mV and has temp where the fluke has mA but no uA but has mV and does not have temp. Both have duty cycle, capacitance, continuity, Resistance, and diode.The biggest thing I noticed with these two meters is the shear difference in accuracy. For instance on a capacitance test of a 100nF capacitor the ExTech gives 76.3 and the Fluke gives 114 both set to nF. The Fluke can also do uF and that comes up at 0.11 as expected. That was just a quick test but I am surprised by how far off the ExTech was.I do not know if it is important to have a uA setting but I am sure mA is good enough. I also noticed the auto ranging on the Fluke is at least 10x as fast.Anyone have any ideas on why the ExTech could be so far off on capacitance I still have to check the voltage accuracy differences and such on my power supply yet?Any thoughts on this Fluke meter do you think it will be more then good enough for my uC projects? I was able to nab this thing off ebay for $144 usd.http://www.fluke.com/fluke/SGEN/Digital-Multimeters/Fluke-77-IV.htm?PID=56126

author: krivx
author_rank: Frequent Contributor
timestamp: April 02, 2013, 01:21:59 pm
content: You have two meters giving different measurements, possibly with different methods. How can you say if either meter, if any, is giving an inaccurate reading?

author: blewisjr
author_rank: Frequent Contributor
timestamp: April 02, 2013, 01:51:15 pm
content: I was using the same basic capacitor of known value on both meters and the one meter was way off the value. So I would assume it is naturally giving a inaccurate value.

author: Lightages
author_rank: Unknown
timestamp: April 02, 2013, 04:31:49 pm
content: krivx is correct. You have no idea which is wrong. One is 14% out the other is 24%. You can only be sure if you have a known and measured value with a known accurate meter. To declare the Fluke correct without this is called "observer bias".Now having aid that I would end to distrust any Extech EX series meter as they are built like shit.

author: PedroDaGr8
author_rank: Super Contributor
timestamp: April 02, 2013, 04:44:00 pm
content: Quote from: blewisjr on April 02, 2013, 01:51:15 pmFirst off, capacitor values are typically +/- 20%. This means that the capacitor could be considered 80-120uF, when you factor in that most capacitor readers are typically 4% or so in accuracy the reading could be 76.8-124.8 and still be considered a correct reading. This doesn't even take into account the fact that capacitance varies with frequency and there are a variety of methods for testing capacitance (some use a known frequency and test the attenuation of the signal in a filter, other charge a capacitor for a known length of time and test the resulting voltage). This is why you can get some widely varying but equally accurate results (not saying the Extech is accurate, just that it COULD be)

author: Lightages
author_rank: Unknown
timestamp: April 02, 2013, 05:05:06 pm
content: What he said (PedroDaGr8)

author: blewisjr
author_rank: Frequent Contributor
timestamp: April 02, 2013, 06:18:46 pm
content: Ok thank you that explains the discrepancy in capacitance no need to be harsh about it. Hence why I asked can anyone explain why they are so different.Now from a voltage/current perspective these meters both seem to be reading quite well the differences are very minute but I think this is due to the meters digit resolution but not positive. With 5V going in from my PSU I read on the extech 5.00 and on the fluke 4.996.Still you all avoid my second question. I asked about the lack of uA on the Fluke and if it would be an issue for microcontroller based work. Everything I have done so far has been around reading in milliamp range and not the microamp range. For instance the current going to a LED through a resistor.

author: zaoka
author_rank: Frequent Contributor
timestamp: April 02, 2013, 08:36:54 pm
content: Its 100nF, not 100uF so there should not be more than 5% + and -.If capacitor is OK and withing 5% both meters are lying

author: Lightages
author_rank: Unknown
timestamp: April 02, 2013, 08:49:15 pm
content: Quote from: blewisjr on April 02, 2013, 06:18:46 pmI don't think anyone was being harsh, but rather just to the point.Quote from: blewisjr on April 02, 2013, 06:18:46 pmIt of course depends on what you are doing. For example if you are trying to check the monotonocity of an A/D or D/A then microamps might be important to see the resolution of the steps. What if you want to measure something accurately at 1 milliamp. Well depending on the rated accuracy of the meter then your measurements could be to unreliable. Better to have that extra digit when the accuracy specs might say something like 1% +10D. I have a meter that has a resolution of 1V. I would not rely on it to measure 12V accurately.

author: RedGrittyBrick
author_rank: Newbie
timestamp: April 06, 2013, 10:56:14 am
content: I have a 77-IV and I think that there are a couple of drawbacks for electronics use- lack of microamp ranges.- lack of picofarad ranges.I had a bunch of capacitors whose markings I couldn't decipher, the 77-IV couldn't help with the low-value capacitors.For microamp measurements I use my ancient Fluke 25. As a second meter, something like an EX330 would also be OK for this.If you do AC measurements then the fact it is averaging and not true-RMS is a disadvantage. The identical looking Fluke 177 is a better buy - true-RMS and better basic DC accuracy.Advantages to me of the 77-IV over the EX330 include:- touch hold - fantastic feature- fast latching continuity beep- safe for use on mains household AC supplyHaving seen Dave's reviews of $50 and $100 meters, I stopped using my cheap multimeters to check that 240V circuits were safe to work on when replacing e.g. lightswitches after turning off at fuzebox/consumer-unit. They're probably OK if you are careful but I'm much happier using an intrinsically safer tool.