Products > Test Equipment
Uni-T UT61E slowly returns to zero in all AC modes. Should I keep it or return?
2N3055:
--- Quote from: myf on August 15, 2023, 09:27:39 am ---Hello !
So "Uni-T UT61E slowly returns to zero in all AC modes" but seems (on video) "very quickly (1 sec. or less) go to the right values".
But usual (electronic linear with capacitors and OpAmp) filters have same rise time and relaxation time in electronics, it is not the case on this DMM.
Numeric Kalman filters have an (recursive) linear formula : Result(n+1) = A.Result(n) + B.NewMeasure(n), it does not match for this DMM.
Do you have any idea about the (low-cost) way used in this case ?
Thanks a lot (and excuse my poor english).
F. from France.
--- End quote ---
AD737 datasheet explains it in detail..
Serg65536:
--- Quote from: Aldo22 on August 14, 2023, 01:44:25 pm ---I just tested this out of curiosity on the An870 and it measures accurately down to about 8Hz. Below that, the measurement becomes unstable.
--- End quote ---
ZOYI ZT219 rebranded as: zotek ZT219, Aneng AN870, richmeters RM870, Zoyi ZT303 (the smaller version).
All of this meters are based on DTM0660
"Maximum display count: 4000/6000 (9999 for frequency and capacitance)" from the datasheet http://www.kerrywong.com/blog/wp-content/uploads/2016/04/DTM0660DataSheet.pdf
So no 19999 real counts on this multimeters is possible. Only through multisample average! This means: you are obliged to wait...
And no real mV resolution also.
Kleinstein:
--- Quote from: myf on August 15, 2023, 09:27:39 am ---Hello !
So "Uni-T UT61E slowly returns to zero in all AC modes" but seems (on video) "very quickly (1 sec. or less) go to the right values".
But usual (electronic linear with capacitors and OpAmp) filters have same rise time and relaxation time in electronics, it is not the case on this DMM.
Numeric Kalman filters have an (recursive) linear formula : Result(n+1) = A.Result(n) + B.NewMeasure(n), it does not match for this DMM.
Do you have any idea about the (low-cost) way used in this case ?
Thanks a lot (and excuse my poor english).
F. from France.
--- End quote ---
The fitler with some RMS chips is nonlinear and it takes considerably longer to go down than up. The time visible for the last few digits to go down still looks too long. Because of the relatively large capacitor needed some meters use electrolytic capacitors and these can have rather high dielectric absorbtion on top of the aready slow time constant.
Besides the filter at the RMS chips there is also usually an AC coupling capacitor to measude only the AC part - this capacitor can also give settling, especially in the 9 V to short test.
The lower frequency limit is usually not a brick wall, but a more gradual decay like a 1st or 2nd order high pass. One part is the input capacitor and the other is the fitler at the RMS chip that at low frequencies makes the chip no longer follow exact RMS response (less weight to the peaks). The first thing is usually the accuracy suffering.
It is normal for analog RMS chips to take some time to settle, especially the step down. The response in the video is still too slow.
Some cheap DMM use digital RMS and this way have nearly instant response. However this usually comes with a limited bandwidth.
Aldo22:
--- Quote from: Serg65536 on August 15, 2023, 12:07:25 pm ---
--- Quote from: Aldo22 on August 14, 2023, 01:44:25 pm ---I just tested this out of curiosity on the An870 and it measures accurately down to about 8Hz. Below that, the measurement becomes unstable.
--- End quote ---
ZOYI ZT219 rebranded as: zotek ZT219, Aneng AN870, richmeters RM870, Zoyi ZT303 (the smaller version).
All of this meters are based on DTM0660
"Maximum display count: 4000/6000 (9999 for frequency and capacitance)" from the datasheet http://www.kerrywong.com/blog/wp-content/uploads/2016/04/DTM0660DataSheet.pdf
So no 19999 real counts on this multimeters is possible. Only through multisample average! This means: you are obliged to wait...
And no real mV resolution also.
--- End quote ---
I didn't mean to say that the An870 is better, I was just interested to see if the UT61E really gives up below 45Hz.
I mean, 5Hz below the most famous frequency! ;)
Veteran68:
--- Quote from: Serg65536 on August 15, 2023, 12:07:25 pm ---
--- Quote from: Aldo22 on August 14, 2023, 01:44:25 pm ---I just tested this out of curiosity on the An870 and it measures accurately down to about 8Hz. Below that, the measurement becomes unstable.
--- End quote ---
ZOYI ZT219 rebranded as: zotek ZT219, Aneng AN870, richmeters RM870, Zoyi ZT303 (the smaller version).
All of this meters are based on DTM0660
"Maximum display count: 4000/6000 (9999 for frequency and capacitance)" from the datasheet http://www.kerrywong.com/blog/wp-content/uploads/2016/04/DTM0660DataSheet.pdf
So no 19999 real counts on this multimeters is possible. Only through multisample average! This means: you are obliged to wait...
And no real mV resolution also.
--- End quote ---
Interesting. I had not seen this called out before. I always assumed the 20K count of the AN870 and it's brethren was legit. I have an AN870, have never used it much, as it sits in a niche better served by my higher-end meters (unlike the more compact Aneng/Zoyi 8008/8009 formfactors that are quite handy for most portable/cheap meter uses cases). It also has a rather cheap quality feel for its size, which doesn't instill confidence when handling. But I see it referenced often as a big bang-for-buck meter with a purported accuracy and precision that rivals much more expensive meters. Seems suspect if what you say is true.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version