Lcr meters, how cheap is too cheap?

[claytonedgeuk]

Whilst messing around with transistors I got tempted to buy one of the cheap mk328 lcr meters for measuring transistors and it's now coming in handy for measuring capacitors as well.

Now though I am getting a sense as to how in accurate this is with subsequent measures of the same capacitor in a fixed position reporting as low as 9300pf and as high has 10400pf off the same unit.

So my question is how high up the ladder do I need to climb to get to a sweet spot of repeatability if not accuracy. 

The de5000 seem to have a fairly good following here...and the peaktech lcr40 looks interesting but in either case I don't want to be asking the same question in a few months wishing I had forked out for a handheld agilent 1733c!

So clever colleagues...what have been your experiences?


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[claytonedgeuk]

Whilst messing around with transistors I got tempted to buy one of the cheap mk328 lcr meters for measuring transistors and it's now coming in handy for measuring capacitors as well.

Now though I am getting a sense as to how in accurate this is with subsequent measures of the same capacitor in a fixed position reporting as low as 9300pf and as high has 10400pf off the same unit.

So my question is how high up the ladder do I need to climb to get to a sweet spot of repeatability if not accuracy. 

The de5000 seem to have a fairly good following here...and the peaktech lcr40 looks interesting but in either case I don't want to be asking the same question in a few months wishing I had forked out for a handheld agilent 1733c!

So clever colleagues...what have been your experiences?


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i should give an example

months ago i whimsically bought some capacitors (brand : illinois capacitor 4.7u). the pdf states that the ESR is less than 10m ohm. cheap, must have been clearance. but i was wrong, or rather, the factory pdf IS WRONG.

when the item arrived i just though i measure the ESR for fun with the cheap ching chong LCR, it appears to be around 1 ohm. i thought it must be broken, but after some sanity checking with other known low ESR caps, i think all the illinois capacitor got to be wrong. they are ALL at around 1 ohm (instead of milli ohms). because i also have a bad ching chong capacitor which measures about 0.5ohm ESR, and it is still 0.5 ohm.

i called up E14, their technician asked me what LCR did i use to check it, i told them. they of course do not trust ching chong LCR. they conducted their own tests. their tests show ESR of over 3 OHM ...

they later discovered the PDF is in error, the spec is not in milli ohm ... but OHM.

there is no way i could get good repeatability from this ching chong LCR, but i can use it to tell bad apples. its just $10 bucks worth of standard.
for repeatability, i think its going to cost $xxx. or unless you make the superb ESR meter by Jay diddy P (in 1 of the EEV threads)

as a reminder, whenever i see illinois capacitor, i AVOID LIKE PLAGUE. they have started to appear in mouser very cheaply as well ...

Well that is food for thought.  Perhaps the caps I have been testing have been rubbish as well.  Shame the poor quality accumulates rather than cancels out.    thanks for the reply.

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[joseph nicholas]

I have the cheapy T3 (I think) component tester.  It has enough code to sus out a wide variety of transistors, resistors, capacitors, etc.  Capacitors probabily need to be tested out of circuit at their maximum voltage to get a true picture of functionality.  It also helps to compare them to a known good one just as a sanity check.

[Retep]

Did you run the calibration routine on your component tester (startup with all pins shorted, follow the on-screen instructions)?

I've got two of those Atmel AVR 328 based component testers. In my experience the results they produce are pretty consistent (often 1 count difference or less) no matter how I connect the component. The accuracy of these units isn't great but adequate for most purposes. For out-of-circuit testing I tend use it more than the DE-5000 and other more expensive meters I have. I don't use it to determine component values in-circuit because that is by definition unreliable (not matter what meter you use).

[claytonedgeuk]

Did you run the calibration routine on your component tester (startup with all pins shorted, follow the on-screen instructions)?

I've got two of those Atmel AVR 328 based component testers. In my experience the results they produce are pretty consistent (often 1 count difference or less) no matter how I connect the component. The accuracy of these units isn't great but adequate for most purposes. For out-of-circuit testing I tend use it more than the DE-5000 and other more expensive meters I have. I don't use it to determine component values in-circuit because that is by definition unreliable (not matter what meter you use).

I hadn't come across that!  Thanks for the tip.  Really encouraging though you still use that when you have a de5000.  Is it far off from the at328 meters in absolute terms?

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[joseph nicholas]

I keep the recommended calibration capacitor with the tester.  I don't calibrate it regularly because the ching chong unit has won my confidence and it has not failed me yet.  The only enoying thing about it is it shuts off way too fast so 2 or 3 tests are needed to read the values.

The thing even reads Mos-fets.

The best 10 dollar piece of equiptment I got from China.

[Retep]

I hadn't come across that!  Thanks for the tip.  Really encouraging though you still use that when you have a de5000.  Is it far off from the at328 meters in absolute terms?

It depends on the capacitor and the settings used on DE-5000. For example if I use the test capacitor that came with the component tester, the component test reports 225.8 nF while the DE-5000 reports 226.8 nF. That is close enough for me. However electrolytic capacitors are a different story; if I measure a random electrolytic capacitor from my stash the component tester reports 125.9 uF, but the DE-5000 reports 113.84 uF (@ 1 kHz). This is quite a difference. Now if I use my Fluke multimeter it reports 131 uF, and my cheap Voltcraft VC850 reports 128.6 uF for the same capacitor. So which one is right (if any)?

One thing to keep in mind is the capacitance of a capacitor is not as straightforward as it seems. If two different meters report different values that doesn't mean that one is wrong and the other one is right (or both are wrong); it could even be that both are right(!). That is because the capacitance of a capacitor is not a fixed value independent of the conditions (such as voltage, frequency..etc). That is why datasheets (should) report the testing conditions/methodology. It also is the reason why on the DE-5000 you can specify the measurement frequency. For example if I set the measurement frequency on the DE-5000 to 100 Hz the electrolytic capacitor I mentioned above measures 121.7 uF, when I set the frequency to 10 kHz is measures 101.7 uF, when I set the frequency to 100 kHz it doesn't even recognize it as capacitor. It gets even worse when measuring the ESR of a capacitor.

The main reason I tend to use the component tester more often than the DE-5000 is convenience; just insert the component press the button and the result is "close enough" for most uses. It is also a lot smaller than the DE-5000 so it tends to be within arms reach on my (small) bench. The DE-5000 is more versatile tool to determine the characteristics of capacitors and inductors since you can specify among others the measurement conditions (which is necessary if you need to compare against a datasheet), but that makes it also harder to use and more likely to confuse you. Another advantage of the DE-5000 is that can measure capacitance in the low pF range (though I believe that recent versions of the component tester firmware have improved in this area).

When I started in electronics (more decades ago than I'd like to admit) I would have absolutely loved having something like the component tester.

[claytonedgeuk]

I hadn't come across that!  Thanks for the tip.  Really encouraging though you still use that when you have a de5000.  Is it far off from the at328 meters in absolute terms?

It depends on the capacitor and the settings used on DE-5000. For example if I use the test capacitor that came with the component tester, the component test reports 225.8 nF while the DE-5000 reports 226.8 nF. That is close enough for me. However electrolytic capacitors are a different story; if I measure a random electrolytic capacitor from my stash the component tester reports 125.9 uF, but the DE-5000 reports 113.84 uF (@ 1 kHz). This is quite a difference. Now if I use my Fluke multimeter it reports 131 uF, and my cheap Voltcraft VC850 reports 128.6 uF for the same capacitor. So which one is right (if any)?

One thing to keep in mind is the capacitance of a capacitor is not as straightforward as it seems. If two different meters report different values that doesn't mean that one is wrong and the other one is right (or both are wrong); it could even be that both are right(!). That is because the capacitance of a capacitor is not a fixed value independent of the conditions (such as voltage, frequency..etc). That is why datasheets (should) report the testing conditions/methodology. It also is the reason why on the DE-5000 you can specify the measurement frequency. For example if I set the measurement frequency on the DE-5000 to 100 Hz the electrolytic capacitor I mentioned above measures 121.7 uF, when I set the frequency to 10 kHz is measures 101.7 uF, when I set the frequency to 100 kHz it doesn't even recognize it as capacitor. It gets even worse when measuring the ESR of a capacitor.

The main reason I tend to use the component tester more often than the DE-5000 is convenience; just insert the component press the button and the result is "close enough" for most uses. It is also a lot smaller than the DE-5000 so it tends to be within arms reach on my (small) bench. The DE-5000 is more versatile tool to determine the characteristics of capacitors and inductors since you can specify among others the measurement conditions (which is necessary if you need to compare against a datasheet), but that makes it also harder to use and more likely to confuse you. Another advantage of the DE-5000 is that can measure capacitance in the low pF range (though I believe that recent versions of the component tester firmware have improved in this area).

When I started in electronics (more decades ago than I'd like to admit) I would have absolutely loved having something like the component tester.

Thanks a bunch for that detailed reply.  It can be difficult to know where to set expectations with this kind of stuff as you are early in the process of gaining familiarity.  That really helps.

I hadn't really understood the relevance of multiple frequencies for measuring capacitance, but that makes a great deal of sense.  Align it for the frequencies you are using it with and measuring it there. 

A great help!

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