Battery cover and case have metal thread insert screws. PCB has self-tappers.
More components under the LCD, which would need to be unsoldered to see.
Seems reasonable from a minimum 100mA DC (Cheap chinese 5A lab supply.). Not sensitive to earth magnetic field, but is sensitive to stray fields from electrical wiring.
Fluke 1507 earth bond test current sensing seems a bit variable. (Three separate runs.)
The PCB in my Amprobe AMP-25 is virtually identical.
Mine always reads 120-140mA in AC mode, with no way to zero it out, although LPF mode is better at around 50mA. But it is still accurate at values just above that. So if I give it 250mA AC, it is pretty much spot on.
DC accuracy seems similar to what you've observed.
Major gripes are no min/max/average, no peak/inrush in DC mode, no zero/relative in AC mode.
I've attached the calibration procedure for the AMP-25 in case anyone needs it, perhaps it is the same for all of them.
The Appa version quotes slightly different accuracy. 60A range 1.5%+10 digits (vs 1.5%+25d). But says accuracy only covers 5-100% of range. So less accurate <3A.
Mine reads zero in AC mode with no load, seems to not react to AC wiring outside clamp.
“Smart data hold” will flash screen and beep if current increases 50 counts from held value. (Amprobe doesn’t say the beeper beeps for this, just flashes screen.)
Interesting that it reads zero in AC mode. Can it properly detect low AC currents, or is there a bit of dead zone at the low end?
I think the residual reading on the AMP-25 is very common, I see it a lot in photos. Amprobe tech support said it was normal.
For my tool bag I typically carry the AM-47 along with the AMP-25. Gets most jobs done without much size/weight.
I think the residual reading on the AMP-25 is very common, I see it a lot in photos. Amprobe tech support said it was normal.
Wondering if that is AC mode or AUTO(default). In AUTO mode it picks up stray fields because it will sense in DC mode. Various video bloggers claim the directional sensitivity of DC clamp meters to be due to earth’s magnetic field and show changing readings with meter orientation. Mine did this inside but not at all outside away from mains wiring and appliances. Clearly this is AC current interference and not earth magnetism.
Mine will easily register 100-250mA (DC) in AUTO mode that changes with proximity and orientation.
Otherwise I presume a non-zero could be adjusted out using the trimpots. Manual says VR53 and VR54 are DC zero offset - ???coarse and fine adjust. If what you are seeing is baseline DC offset, it can be zeroed.
Did a quick test on a 12V 20W iron transformer halogen desk lamp (live twin arms). Got 660-680mV with repeated measurements (maybe it has a 10W bulb in it?). In AC mode, has no trouble returning to zero. In AUTO mode, can switch from AC during measurement back to DC when clamp is empty anywhere from 20-140mV random or zero AC if it can’t find a DC source.
Tried a 20W halogen running AC switchmode transformer. Only get 20mA AC. Frequency must be too high to register.