Products > Test Equipment
AN8008 US $19, 9999count, 1uV, 0.01uA, 0.01Ohm, 1pF resolution meter
Kalvin:
--- Quote from: EEVblog on July 17, 2017, 10:55:06 am ---
--- Quote from: evava on July 17, 2017, 09:42:59 am ---Guys, calm down.
I like all your answers, they explain many things.
But, IMHO the strongest point of this $19 meter is 1uV resolution, not any of his Amp range. No need to discuss Amp ranges so deeply.
--- End quote ---
The vast majority of electronics works on mA, not uA.
This meter fails to cover the most common current ranges in electronics design with any degree of decent resolution.
--- End quote ---
In some of the latest microcontroller projects I have been involved we have needed to be able to measure the standby current consumption in 5uA - 10uA range with 100nA resolution in order to be able to observe how the average current consumption changes when we change something in the circuit or in the software. However, when the device wakes up, the current consumption will be around 10 mA - 20 mA. This is typically a problem related to the burden voltage as the device fails to operate due to the voltage drop caused by the sense resistor inside the DMM. However, placing a low leakage and low Vf diode across the DMM inputs will take care of that problem quite nicely and limit the burden voltage to few hundred millivolts. Of course the current measurement is not accurate any more at higher currents when the diode starts conducting, but this arrangement has worked quite nicely in practice.
Crumble:
--- Quote from: evava on July 17, 2017, 09:42:59 am ---[...]
But, IMHO the strongest point of this $19 meter is 1uV resolution, not any of his Amp range. [...]
--- End quote ---
I totally agree with that. This meter might not be entirely practical if it is your only one due to the missing ranges (and other quirks), but it has some unique features that might complement other meters if you don't have a lot to spend. Yeah, if you already have a 7,5 digit Keysight lying around you might not be especially impressed, but now I can add a µV resolution measuring option to my "lab" for just ~US$20. I have got one on its way! ;D It looks however like the designers had no good idea if they wanted it to be an electrical or electronical measurement device. Its square wave output sounds interesting, but I could not think of one single way I could implement it practically in an actual circuit due to the lack of flexibility and range. Personally, I would have inserted a third shunt in the meter and I would have used the position on the knob to select it. With dedicated temperature meters available I don't really need that as an option, but one could argue in its favour.
I already own an AN8002, and I do like it in a number of respects. It has relatively high counts for a €13 meter (this one's even better) and is quite accurate and has no pots in it. I had an old Uni-T which did, and it changed over time to be out by as much as 10% (in every range) until I found the proper pot to tweak (cause there's no documentation on that). :palm: The capacitance goes down to pF resolution and is quite fast. It is also high impendance in mV range, which can be useful for some applications. It mV range also allows for measuring current with in-circuit shunts (but you'll have to design these in, which I sometimes do), because when doing electronic work breaking the circuit open and inserting a meter with its sometimes high shunt resistances and/or long inductive leads might very well interfere. The AN8008 does have an option the AN8002 does not: manually changing ranges. I often find myself wanting to do so, but this feature lacks on the AN8002. I would have considered that a more useful feature than the present "Hold" function.
BTW with my AN8002 the diode check voltage is above the battery voltage. It puts out 3,25V while I use Ni-MH rechargable batteries that are at 2,6V (these values were measured with my unit, but might differ with other ones). It must have some kind of small charge pump in it. I must note it only delivers very low currents at this voltage, but I could light two red LEDs in series very faintly and see their forward voltage (some meters seem to put out the voltage, but just not measure it above a certain level, don't know why).
plazma:
--- Quote from: Crumble on July 17, 2017, 09:06:40 pm ---.....
The AN8008 does have an option the AN8002 does not: manually changing ranges. I often find myself wanting to do so, but this feature lacks on the AN8002. I would have considered that a more useful feature than the present "Hold" function....
--- End quote ---
You can add REL, RANGE & MIN/MAX buttons to AN8002.
ocw:
I modified my AN8008 to provide single digit mA readings with 3 digit resolution. I replaced the regular mA/A readings with the ability to measure currents below 100 mA with a XX.XX mA display. Currents below 1A are measured with the same XXX.X mA display. 1A is now the maximum current which can be measured.
I replaced the 0.01 ohm shunt resistor for the A/mA jack with a 0.10 ohm 0.5% resistor which I had in stock. Attached is a picture of the upgraded meter measuring 2.5000 mA current. On the left the meter is in the uA position, the test lead is in the A/mA jack and the meter reads 2.59 (uA) [3.6% high]. On the right I've switched to the mA position but the reading has gone down to 21.9 (mA) [12.4% low]. I obviously haven't corrected the position of the decimal. Remember, the actual current through the meter is 2.5 mA is both cases.
About a 0.12 ohm resistor will correct the magnitude of the of the reading when the meter's switch is in the mA position. But, I prefer having the decimal point in the correct position. Being in the A/mA jack will remind me that mA is the actual display units. I might purchase some 0.10 ohm resistors with less precision hoping to get one a bit low in value which will improve the mA reading's accuracy when the meter's switch is in the uA position.
NivagSwerdna:
I'm quite tempted by this meter as my old MasTech doesn't have a uA range but now in two minds due to the lack of low mA ranges.... tricky!
... however I really do need something to measure in the 10uA type area MCU in standby for battery applications.... what to do! |O
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