I opened up my PeakTech 3725 multimeter, questionable 10A conductive tracks

[Franki]

hi there

Opening up my PeakTech 3725 3 1/2 digit multimeter reveals a supposedly maximum 10A conductive track of about 1.6 mm minimum width @70µm thickness. I'm wondering whether this may be a little too optimistic, even for a conductive track. How high would the temperature be there in theory? On the other hand, there is only one way to find out for sure...

Apart from that, it actually seems a decent DMM:
-V|A|Ohms calibratable(when opened) and it gets shipped calibrated
-quiet acurate, though I haven't checked it against a calibrated device yet
-gold plated measuring contacts on the DMM, but the shipped measuring lines aren't - this is a bit of a turn off as it doesn't make much sense :|
-shielded with some metal foil (HF shielding?), but unfortunately only from the back, not the front or sides, this would make a HF-shielding pointless though :|

I'm looking forward to send some pictures for you guys in the distant future.

[Bored@Work]

PeakTech does badge engineering. That is, they get their "PeakTech" badge slaped on instruments they order from manufacturers all over the world.

When you opened it, did you have an indicate who the original manufacturer of that particular meter is? Any hints on the PCB, for example?

[Franki]

PeakTech does badge engineering. That is, they get their "PeakTech" badge slaped on instruments they order from manufacturers all over the world.

Yeah, that's well known

When you opened it, did you have an indicate who the original manufacturer of that particular meter is? Any hints on the PCB, for example?

I'm going to look at it as soon as I have some spare time.

[saturation]

Pictures please, worth 1000 words.

[mikeselectricstuff]

The question is no so much whether the track can take 10A but whether it can take whatever current is needed to blow the fuse without blowing first to protect the fuse.
1.6mm seems rather puny.....

[alm]

Keep in mind that it may only be rated for the full 10A for 30s or so, it may be relying on thermal inertia to keep the temperature down.

[Neilm]

Opening up my PeakTech 3725 3 1/2 digit multimeter reveals a supposedly maximum 10A conductive track of about 1.6 mm minimum width @70µm thickness. I'm wondering whether this may be a little too optimistic, even for a conductive track. ck, not the front or sides, this would make a HF-shielding pointless though

I put the figures into a programme called MiseEL. It is a freeware programme. It says that track would rise about 40 degrees with those parameters. I have tested this in the past and againts real life currents and it is usually reasonabally accurate.

Neil

[tyblu]

According to the ANSI calc, which is only accurate to +100C rise, it'll have about an +180C rise.
http://www.desmith.net/NMdS/Electronics/TraceWidth.html
Is it tinned? That helps.

[Psi]

According to the ANSI calc, which is only accurate to +100C rise, it'll have about an +180C rise.
http://www.desmith.net/NMdS/Electronics/TraceWidth.html
Is it tinned? That helps.

That's for internal layers, for external layers it's only a +38C rise  (for 10A through 1.6mm of 70um copper at 25C ambient).
63C is hot enough to hurt if you held your finger on it, but well within what a normal pcb can handle.

[Franki]

Keep in mind that it may only be rated for the full 10A for 30s or so, it may be relying on thermal inertia to keep the temperature down.

I actually found a label on the scope 10A for 10sec max. This warning is realistic, but a quiet narrow PCB design...

[Franki]

I put the figures into a programme called MiseEL. It is a freeware programme. It says that track would rise about 40 degrees with those parameters. I have tested this in the past and againts real life currents and it is usually reasonabally accurate.

This seems fairly acurate, though the best reliable resistive load I have in that region is a 29.5ohm 1800Watt heating coil within a water boiler for 230Veff mains which would take up about 7.8 Amps_eff...With the labeling reading 10A for 10s max, I dare not to use bigger loads.

As this meter comes without any current clamp, I will need to measure the current directly. Who is sponsoring me a mains circuit opener on a male/female SchuKo plug? I already have a phasing tester.


I noted another thing: the shunt in the meter is presumably made out of tin plated copper and only has a diameter of about 1.6mm or a cross-sectional surface of about 2.0mm². I wonder whether this is the weakest link in the current path...

[Franki]

OK, since I currently have no opportunity to make pictures of it, I'm going to describe it.

The circuit is built on two different PCBs layered on top of each other but separated by about 5mm and interconnected by a soldered in 20pin single layer 2.54mm board to board pin connector which makes it impossible to see what's in between those two PCBs without unsoldering it entirely And lots of other components like caps and resitors are placed at the edge of the other sides of the two PCBs (those without any board to board pin connector) so you really can't see anything in there unless you would have some kind of fibre optics

On the bottom of one PCB are just conductive paths and on top of the other PCB are just uninteresting small jellybean ICs(low power CMOS logic, opamps...). However, there is no sign of any manufacturer at all no matter how close you may look at it, except for the forementioned jellybean ICs' manufacturers
I tried doing that with a 10x magnifying glass and multiple light sources... no luck.

Here are some of the ICs I recognized:
NXP HEF4066BT : 4x bilateral switch
texas instrument LM358 : your standard low-power opamp
Fairchild Semiconductor CD4093BCM : 2x smith-trigger NAND
062 (?unrecognized, maybe TL062, a 2x general purpose low power opamp)
072 (?unrecognized, maybe TL072, a 2x general purpose low noise opamp)

model numbers/production dates/serial numbers are printed on the PCB, but no apparent manufacturer is printed on it, unless you can make it out from the abreviated codes.

Front side:
0731
WF-668 94V0
E249427

UT7CA
120899

Back side:
110899K

mostly boring stuff