Products > Test Equipment
AN8008 US $19, 9999count, 1uV, 0.01uA, 0.01Ohm, 1pF resolution meter
b_force:
--- Quote from: Lightages on June 30, 2017, 04:42:21 am ---If this meter is lying around with its false ratings and someone picks it up to use it where they need the real protection because they see the marks, it could kill them or injure them severely.
--- End quote ---
I seriously never understand this statement?? :-//
Worst thing that could happen is a spark inside a plastic case (= multimeter).
That's absolutely not enough to "KILL" someone.
In my whole professional career I have blown up many things, have seen sparks everywhere and have been shocked more times than my hands can count.
It hurts, but for normal healthy human beings, not walking bare foot on wet soil and not being pinched close to the heart, it's absolutely nonsense to say that this is "super dangerous".
The most dangerous part is that scare up people when it happens and in that moment maybe fall off a ladder.
That could even happen with a decent professional meter.
Only thing you can say, is that it's very inconvenient and 'dangerous' in a sense that you simply don't know what you can rely on.
For someone who is using this multimeter behind a fused line (like at home or a desk), it's not much of a deal.
For someone who is working professionally with high power high voltage lines, which aren't always directly fused, it's a whole different story.
But in these situations you're only allowed to use certified gear anyway.
ocw:
I finally got inside of the meter since the AC current measurements don't seem very stable. I haven't seen a poor connection yet which might be causing that. Regarding:
--- Quote ---Place a 1 ohm resistor across a Pomona 1330-2...
--- End quote ---
There is already a 1 ohm resistor inside of the meter ready to serve that purpose. The 100 ohm shunt resistance for uA current measurement actually consists of a 99 ohm resistor in series with a one ohm resistor. With a little rewiring...
The meter must have been changed from mA current to uA, robbing the full resolution mA measurement capability. On the switch side of the circuit board the voltage, uA, etc input is labeled "V/R/F/mA/Hz/C." Yes, that is mA and C, not uA and square wave.
The board is labeled ZT109 on the switch side. See: http://szzotek.com/en/col.jsp?id=144
I'll have to look for other secrets.
ocw:
--- Quote ---I finally got inside of the meter since the AC current measurements don't seem very stable.
--- End quote ---
While the two digit ammeter for 1 - 10 mA DC readings might have limited value, it is of no use for AC readings in that range.
While I had reasonable accuracy on the AC uA readings from 10 to 1000 uA, things fell apart when I tried to read 1000 uA as 1 mA AC. The AN8008 showed zero mA for that measurement. My next test measurement was at 3.3 mA. The AN8008 generally stayed at a reading of zero with an occasional jump up only to soon return to zero.
My next step is at 10 mA. By then I had a steady reading which was 8% low. At 30 mA the meter became useful with a reading which was only 1% low. By 75 mA and above the meter's surprising accuracy returned with the accuracy typically below 0.2%.
evava:
--- Quote from: ocw on July 16, 2017, 12:05:34 am ---
--- Quote ---I finally got inside of the meter since the AC current measurements don't seem very stable.
--- End quote ---
While the two digit ammeter for 1 - 10 mA DC readings might have limited value, it is of no use for AC readings in that range.
While I had reasonable accuracy on the AC uA readings from 10 to 1000 uA, things fell apart when I tried to read 1000 uA as 1 mA AC. The AN8008 showed zero mA for that measurement. My next test measurement was at 3.3 mA. The AN8008 generally stayed at a reading of zero with an occasional jump up only to soon return to zero.
My next step is at 10 mA. By then I had a steady reading which was 8% low. At 30 mA the meter became useful with a reading which was only 1% low. By 75 mA and above the meter's surprising accuracy returned with the accuracy typically below 0.2%.
--- End quote ---
IMHO, it is very common that TRMS measurement at most multimeters works only at about >5% of the range.
It is usually stated in manual.
Only exception is thermo TRMS converter at some precision meters.
This is the very problem of this meter AC current measuring in these missing current ranges. If only this TRMS converter could be switched off sometimes manually, that would help.
alm:
The true RMS error is usually due to a DC offset in the RMS converter. This offset disappears at higher values because sqrt(ACV^2 + offset^2) tends to ACV if ACV >> offset (which is also why you can not subtract the offset by measuring the output with shorted inputs). So I would indeed not expect good performance near the bottom of the range.
Bypassing the TRMS converter is rarely supported (exception: some meters for the military since they still have old procedures that require an average-responding meter). I guess you could take out the TRMS chip and replace it by a precision rectifier, but that would destroy any TRMS ability and seems like an awful lot of work for this cheap meter.
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