GOT ONE (was Re: Craftsman mini multimeter with K thermocouple )

J. Clarke wrote:
Miss Penny wrote:
On Mar 16, 2:56 pm, EskWI...@xxxxxxxxxxxxxxxxxxx wrote:
In alt.coffee, The Other Funk <bob...@xxxxxxxxxxxxxx> wrote:

20+ years calibrating test equipment including several years at
Fluke. 7 of those years at AT&T Bell Labs.
Digital meter specs in the form of +/- % reading + digits should be
written as +/-(% reading +/- displayed digits) I have never seen
specs given as A/D error for a DMM.

Cool. And very interestng.

What accounts for the loose specs in cheap digital equipment (I am
assuming that +/-n%+5 is not SOTA)? Is it some sort of repeated
rounding error?



what do you want for $10.00 ?

accuracy?

I figure for 10 bucks how bad can it be? Certainly can't be any worse
than the same money spent on coffee at Starbies.

Have one in hand.

It tells me that a kettle of water boiling violently is at 205 degrees.
Both my Taylor quick reading analog thermometer and my Polder digital
agree that the temperature is 210. Says that the snow outside is at 24
while the Polder and the Taylor agree that it's at 32. On the other
hand, all three agree that the room temperature at the moment is 66, so
its error is not anywhere close to constant.

Seems to have more lag than one would expect in an exposed thermocouple
but I haven't tried to quantify that.

The display hardware is capable of 3-1/2 digits and that may be used for
electrical measurments, but for temperature it moves in increments of 1
degree, not 1/10 or 1/100.

The thermocouple connects using two banana plugs, and the wires are
insulated with what appears to be a fiblerglass tube, with a piece of
heat shrink tubing at each end. Not sure what the melting point of the
heat shrink is but at 430 or so playing with the I-Roast it was
definitely soft--hadn't melted quite but was getting there.

Mechanically the external fit and finish are decent. The battery is
installed by removing the back, which is held by two screws tapped into
plastic bosses--from the feel when I tightened them one is already
pretty far along the road to stripping its threads. Inside, the board
appears to have been hand soldered and there's evidence of at least one
rework. Quality of the soldering isn't any great shakes--in my
Heathkit building days I'd have resoldered half the joints--but they
don't look like cold joints, just sloppy.

Doesn't seem to be any adjustment--if I get bored at some point I may
see if I can identify the chip used--if so then it may be possible to
find a way to calibrate it, but that's very low on my list of things to
do.

On balance it's about what you'd expect for a ten buck meter.

--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)


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