Products > Test Equipment
EEVBlog 121GW Multimeter Firmware Details
CDaniel:
No , I don't touch or move anything and it drifts .
You don't use the probes , that is a very big difference .
The problem is not how you should measure for maximum precision pF capacitance , we know and we have RLC bridges for this , but if the meter is comparable with other good multimeters ... who we presume should not drift much and you can use the probes just in case you need to measure something accurate . This is a portable handheld multimeter after all , not to sit in the best conditions
chronos42:
Hi joeqsmith,
to make that more clear: Normaly I do not use a multimeter for measuring low pF values, I have other instruments for this.
But that is not the point. Also the drift is not my major problem.
The problem is: I Connect a capacitor in the pF range to my meter, switch it on and it shows (mostly) the correct value at the first try. Then I switch it off and on again while not touching anything except the switch and now I get a totally different value. Do the same again and I get another different value. When I switch off the meter again, wait some time, switch it on I get the correct value ....and so on...
That is a very strange behavior. I don't know whether this issue was from begin on or not, because I had never tried to measure a capacitor in the low pF range. I noticed this first time after you have mentioned the higher resolution in the capacitor mode and I checked this to look how the 121GW now performs compared with my other meters.
Just for fun.. I did not expect such a crazy behavior.
First I thougt that is a firmware bug of rev. 1.57, but it seems not so.
Your meter seems not affected from this issue as I can see in your video. But CDaniel seems to have the same problem like me.
BTW: Try also the mode button, does this also not affect your meter?
CDaniel:
Yes , more or less I see the same behaviour like you , but not allways . The drifting I see is maybe that difference ...
With short probes it is not sensitive to touching the buttons ... but an issue is an issue , you can't make it dissapear . If you put the hands near the probes ... it's a mess :--
And of course you can see the problem with larger capacitors 1nF-10nF , you don't have to measure something really small .
I doubt it's a hardware issue , they don't know very well to control the chip HY3131 with the firmware ... and if STM32 microcontroller is also new for them it's a very bad combination
1anX:
--- Quote from: chronos42 on November 24, 2018, 10:32:43 pm ---Hi joeqsmith,
to make that more clear: Normaly I do not use a multimeter for measuring low pF values, I have other instruments for this.
But that is not the point. Also the drift is not my major problem.
The problem is: I Connect a capacitor in the pF range to my meter, switch it on and it shows (mostly) the correct value at the first try. Then I switch it off and on again while not touching anything except the switch and now I get a totally different value. Do the same again and I get another different value. When I switch off the meter again, wait some time, switch it on I get the correct value ....and so on...
That is a very strange behavior. I don't know whether this issue was from begin on or not, because I had never tried to measure a capacitor in the low pF range. I noticed this first time after you have mentioned the higher resolution in the capacitor mode and I checked this to look how the 121GW now performs compared with my other meters.
Just for fun.. I did not expect such a crazy behavior.
First I thougt that is a firmware bug of rev. 1.57, but it seems not so.
Your meter seems not affected from this issue as I can see in your video. But CDaniel seems to have the same problem like me.
BTW: Try also the mode button, does this also not affect your meter?
--- End quote ---
Hey chronos what happens if you short the capacitor leads each time before turning on the meter?
By turning the meter on the first time I assume you are charging a discharged cap, but each time you turn off and test again, the cap is already charged from the previous test.
Could this account for the behavior you are seeing?
1anX:
I thought I would run a couple of low cap tests on my meter with V1.57 firmware.
Measured 2 caps of given values, 15pF and 22pF which are at the extreme end of what the meter is capable of measuring and checked values against my DER EE DE-5000 LCR meter.
The GW121 displayed a combined meter and leads, (with alligator clips) capacitance of 0.175nF when turned on. I used the REL function to zero out the combined meter and lead capacitance and then measured each cap. I repeated the turning off and on of the meter and zeroing using the REL function before taking each measurement.
The 15pF cap measured 15.7pf on the DE-5000 and 0.018nF for the first 121GW test measurement and then 0.014nF for the second test.
The 22pf cap measured 22.9pf on the DE-5000 and 0.025nF for the first 121GW test measurement and then 0.021nF for the second test.
Considering the +-2.5%+5, I was pretty pleased with the meter's performance!
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