Meters and Microamps

[stj]

Re: Meters and Microamps

well the bussman/fluke fuse costs about the same as my 61e did!!!
i think they are just fucking people because they know the cost of the equipment!

[eccerr0r]

Re: Meters and Microamps

We with Flukes are getting fleeced!

Interesting:
Fluke (hand): 15A HRC 10x38, I think 600mA HRC for 300mA mode.
Tenma (hand): 10A ceramic 6x25(!!!), 500mA 5x20 for 200mA mode
BKP (bench): 4A HRC 10x35, does not seem to be fuse for 20A mode? Doesn't sound right, perhaps someone put in a 4A HRC because they couldn't find a 20A HRC...
HP (bench): 2A 6x32(?)
Viz (bench): 2A glass heatshrink 6x32 Soldered in circuit
Micronta Analog (hand): No fuse (3A max measured current), ?? for 300mA mode.
Eico Analog (hand...): No fuse (10A max measured current)
HFT Freebie (hand) : No fuse (10A), don't remember for 200mA mode.
Tektronix (bench): 2A glass 6x32
Mastech (hand): 10A noname ceramic 6x32

[stj]

Re: Meters and Microamps

out of curiosity,
i wonder how much blood it would cost to buy a fuse from keysight!!!

[eccerr0r]

Re: Meters and Microamps

I suspect that common parts the expectation is people buy just like for Fluke from third party vendors... else https://www.keysight.com/find/parts ?

BTW the old HP DMM is so old (pre-Agilent!) that it doesn't even have shrouded jacks, plus the fact it was meant to be a low current (2A) benchtop so no HRC fuses in that thing...

[stj]

Re: Meters and Microamps

but now they push HRC for the 440mA range!
bastards.

[eccerr0r]

Re: Meters and Microamps

My Eico VOM 10A or even 500mA range has no fuse at all... Pin attach probes, no shrouding. Who needs fuses?

"Back in my day we had to walk to school in the snow up hill, both ways!"

[stj]

Re: Meters and Microamps

did the old AVO-8 have fuses?

[eccerr0r]

Re: Meters and Microamps

Looks like at least the AVO-8 Mark 7 version had fuses... The M.7 looks sort of like 1980s design perhaps. Older versions of the AVO-8, no idea.

I suspect that most 1990s multimeter designs started using HRC fuses?

[stj]

Re: Meters and Microamps

most early 90's ones had 20mm glass fuses.
so HRC - define "High"

[eccerr0r]

Re: Meters and Microamps

Hmm...yeah I suppose the early 90s still used 80s like designs, glass...
but later on in the decade the ceramics came in...

Then again if there's no regulations, there's no need for these, and all those eevblog naysayers giving crap to cheap chinese crap designs...never needed to replace the fuse they never needed...

[redwire]

Re: Meters and Microamps

I remember at Radio Shack guy demanding a refund for his analog multimeter. He wanted to check if a mains outlet was 15A so he put his meter across it. The rotary switch basically exploded
All my old 80's multimeters have no fuse on the 20A range, it's trial by fire. But engineers in the lab blow fuses in multimeters and I'm the guy buying new ones, the boss thinks I popped them, I just wanna measure current.

A long time ago Fluke pushed for safety, patented many aspects of multimeter input protection, bigger fuses etc. So they pioneered 1010 Safety Standard which became 61010 the "multimeter standard". I think there were too many incidents of people using the current function and hitting high power systems.

A fuse's voltage rating is dictated by it's length, we would all like 5x20mm fuses good for 1,000V but that's too short, so we get 38mm piggies.

I can't pay $50 for a multimeter fuse nowadays. I could hoard them and make a ton of money off their appreciation. Not as much as Bitcoin, but maybe FuseCoin... lol

[stj]

Re: Meters and Microamps

i wonder if that's why fluke used to sell meter probes with a fuse in the cable?

as for switches exploding,
i got a free meter from a guy that had the protection diode split and the switch contact and tracks for current completly burned away.

i dont know what he did, but i dont care.
i just blocked-up the socket for current, replaced the diode and gave it to a friend who just uses it for voltage and continuity.

[eccerr0r]

Re: Meters and Microamps

When I got the Eico VOM (likewise was free) it had a burned resistor in it...

"Gee I wonder how it burned!"

Then again I wonder if fuses are in line with the non-current carrying modes especially with DMMs. Analog VOMs can actually pass significant current in the Rx1 mode...

(That Eico meter was pretty broken when I got it. I had to replace resistors, AC rectifier, and the current shunt (which was incorrect for the application, not because it blew... Imagine blowing the current shunt... ) )

[stj]

Re: Meters and Microamps

lol
i'v seen a current-shunt that desoldered itself before.
people dont read the manuals - there is a duty-cycle for high current readings.
something like 15seconds use, 2min's cooldown.

till you get some fool running 8A through the meter for an hour while he monitors some running kit!

[redwire]

Re: Meters and Microamps

Fuse wire - I've seen many different alloys, tinned copper seems fine but knockoffs are higher resistance likely aluminum, as they are in automotive fuses. You don't want a (high resistance) fuse that runs really hot melting things.
I want to get some fuse wire, that's the main ingredient in the $50 caviar.

The fuses protect only the current shunts (and the user) but not the voltage/ohms functions.
There are pics of a totally roasted Brymen - I figure the guy connected it to MOT and burned the MOV's and resistors on both channels, they arc'd to each other which is not supposed to happen. No fuse there.

[eccerr0r]

Re: Meters and Microamps

That Eico's shunt wire was exactly that - a wire - and apparently someone substituted a copper wire when assembling it for whatever reason. So even at 10A it had no voltage across it, probably had more voltage across the probe wires.

I didn't have any resistance wire to repair it, but I did have a pile of 0.2Ω 2W resistors. It should have been 0.025Ω so I piled eight of the resistors in parallel. At 10A, this pile of 2W resistors should survive just fine I think, and now the Eico can once again measure 10A current.

I wonder if the fuse wire is Bussmann/Littelfuse/Siba/...'s secret sauce...and why the caviar is $50.

[stj]

Re: Meters and Microamps

shit happens.
there's a thread here somewhere, where a guy tried to test a fence charger with a fluke and a uni-trend pocket meter.
fucked the fluke, but the uni-t actually survived and read something like 3KV even though it was only 600v rated!!!!
i guess the little pocket ones have no mov's in them.

[stj]

Re: Meters and Microamps

siba lists the resistance of their fuses in the datasheets.

[eccerr0r]

Re: Meters and Microamps

I'd imagine all reputable fuse companies should report DCR of their fuses, seems Siba is one like Bussmann and Littelfuse.

---

If I knew I had to probe 3KV I'd go with the Eico that actually has a 5KV range - well past all the DMM's I have

(I do have a 66MΩ and a 100MΩ HV resistors that I could use if push comes to shove though will need to do math to get the actual voltage...)

[redwire]

Re: Meters and Microamps

Looking at copper fuse wire, Onderdonk's equations from the days of the telegraph:
20AWG (0.812mm) matches the DMM-11A curve e.g blows 10 seconds 43A. 22AWG is 10 seconds 30A.
35AWG (0.413mm) matches the DMM-44/100 curve e.g blows 10 seconds 1.5A and 36AWG is 10 seconds 1.2A
I think the sand filling should make the results higher due to the cooling, so 22AWG and 36AWG caviar should taste good

Ali seems to offer only aluminum fuse wire, half the melting point of copper. Can't solder it and CCA probably sucks for a good connection.