The context there is key too. While I'd not measure a countertop or whatever in millimeters, it would make no sense that anything in a kitchen would be measured thicknesses of paper.
We (in the US) use "guage" for wire and sheet metal. We also use "guage" for measuring really thin stuff like plastic films. In the last case, it's a completly different unit, but with proper context won't confuse anybody.
Question for the metric woodworkers. Does anybody cut a piece of wood to
317mm or 429mm or other off numbers when building a house or handing a door or installing a countertop?
Fair enough. I noticed construction practices are very different by country. We have some really flimbsy accepted practices in the US for new construction. The obsession here with insulating everything results in buildings that will mold and rot from the smallest of water leaks. You can flood and older building and since it's not sealed up like a plastic freezer bag, it will dry out and be fine. The codes vary from state to state as well. Some places are more tolerant of fiery death traps and buildings that collapse while being built.
Whyever not? Even the cheap ones usually state you can use them up to 1000 volts. I've used them on 240 and 415 just fine. I used one on 2000 volts once, and it just failed inside, not even smoke or noise.
How well do these things work measuring dodgy waves like from a cheap UPS or invertor?
I've replaced outlets (240V, not the namby pamby USA stuff) without turning off the power - other outlets on the same circuit were being used in the office and I saw no point in interrupting them.
Just keep your fingers off the metal things and don't short stuff together. Wear goggles and gloves if you want to be a girl about it.
Try shorting two phases together with 500A cables. That causes lots of smoke, a fire alarm, 3 fire engines, and a visit from the power company. Do not ever employ Irish electricians.
I find it crazy that you can select volts and have the wires in the amps= holes. The switch should change the contacts. I've broken a meter doi= ng that, just measuring the voltage on a car battery. =A3100 meter, but= UNFUSED FFS! At least the mA range was fused, but they couldn't be bot= hered putting in a 20A fuse for the big range....
Because I have seen what damage can be done with those circuits.
I have also seen some safty films that the Fluke meter company put out. Say you take your HF meter and by mistake have it on the ohms or amp range. Normally an internal fuse would blow. However there is enough power in the circuits to arc over the fuse, the meter leads instantly almost explode or look like an arc welder. If you have one hand on each lead it is possiable the insulation will melt off and maybe into your hands. You could also become part of the circuit and fry.
Isn't that really hard to work out? We use cross sectional area in mm. Which is really easy to imagine. With the added bonus that a higher number is thicker. It's also pretty handy as a rough guide that 1 square mm carries 10 amps.
Seriously? Wow. Why would you nbot measure a thickness in a unit of distance?
We use microns.
Depends if something else is in the way. I'd always try to use round numbers.
sheet metal in mm (1.6mm, 0.65mm etc...) plastic sheet in microns 40um etc. electric wire in square mm. fencing wire in mm diameter.
Yes, if that is the right size. buildings are usually specified in multiples of 100mm. often multiples of 300mm or 1000mm furniture usually in multiples of 25mm
Factory door sizes are 620mm + multiples of 50mm, but not all openings are the right size for the factory door.
Timber sizes for dressed finger-jointed framing timber are accurate to withion 0.5mm are are certain preferred multiples of 5mm eg: 70x35 used mainly for non-structual walls. 90x45 used mainly for structural walls.
The stud spacing and top-plate height will typically be some multiple of 50mm So a lot of the cutting for studs, and blocking is at multiples of 5mm. that's if you're not using pre-fabricated framing.
Carpenters use millimeteres. they say centimeters are for tailors, and inches are for cobblers.
The separate amps jacks exist for at least two reasons:
1) If the range switch also switched in/out the current shunt, then the user could accidentally create a short circult across the probe tips simply by turning the range switch to or across the amps measurement ranges. Even if they were quickly turning /across/ the amps settings ranges, a brief short circuit would be created, which would cause damage to the meter as well as the device under test depending upon what was connected at the time.
2) By having the amps jacks separate, the range switch itself does not have to have contacts beefy enough to carry the current for the amps settings. Remember, when measuring amps, the current being measured flows *through* the meter itself. This would require very different (and likely much more expensive) range switch contacts.
Some meters do have sensors for the amps jacks that sound an alarm if the probes are inserted in the amps jacks but the range switch is on a different setting than amperes.
Some meters have range switches that rotate through a full 360 degrees with no stops - there would be no "end of the dial" in those instances.
And even with an 'end of the dial' there is still the possibility of landing 'off by one' while turning the dial.
The same idiot who'd leave the leads plugged into the amps jacks and then attempt to measure the voltage of a car battery (or some other low impedance high current voltage source).
I suspect you would find changing the range switch while connected is much more common than your response implies. Esp. for switching up/down a range for meters that are not auto-ranging.
Which also equates directly to added expense vs. having the user themselves be that "relay". And for battery powered meters, shorter battery life (due to the current consumed by the relay coil).
It is also possible (this is a guess in my part) that the CAT ratings specify separate amps jacks for an added safety factor of "user must deliberately move lead to obtain short circuit through meter".
As well, the user who'd leave the leads plugged into amps, and then try to measure voltage on car battery or other high current source is also just as likely to leave the range switch in the amps setting (after having measured current somewhere) and subsequently try to measure voltage. It is not possible to fully protect users who don't pay attention from doing stupid things. Either they forget to unplug from the amps jack, or they forget to switch away from the amps range, either way they get a local fireworks display of their own doing.
Wrong. You adjust the dial to what you want to do, not remembering what= you were measuring yesterday. Having only one thing to change makes it= way easier to get it right.
It only has to get over 20 amps to f*ck the meter.
Meters should always auto range. Mine all do, and I've never even consi= dered adjusting the dial while it's connected. I'm not going to change = between resistance, current, and volts and want to leave it connected to= the same thing.
ot
No, because you save on an extra socket.
Latching relays use very little indeed, like the one in my room thermost= at. 2 AA batteries last years.
Then they're fools, because now "user can obtain short circuit by forget= ting he was measuring current yesterday, or because a colleague was with= out him knowing". If it was selected on the dial, there is no possibili= ty to make a mistake. You select what you want and that's what you get.= It's illogical to have one thing pointing at volts while another thing= is expecting current!
Anyway, a simple fuse would solve all this. All you lose if you make a = mistake is a fuse, not the internal workings of the meter, the test lead= s, the thing you're testing, and possibly your face.
y
Nope. I pick up a multimeter and set it to what I'm about to measure. = Same way as I don't drive into my house because I left my car in forward= gear yesterday.
People make mistakes. The best equipment prevents this. My VW Golf for= example would not allow me to select 1st gear when going 100mph. It wa= s quite clever in fact. I could do that on purpose and it would drop on= e gear at a time to slow the car as quickly as possible to assist the br= akes in an emergency. And yes I did try it a few times, one time I scar= ed the shit out of the passenger (who had never seen an automatic gearbo= x before).
I often leave the leads connected to a Simpson 260 and change voltage ranges. Where I worked there were so many wires in a conduit carrring
120 VAC control voltage it was difficult to tell if the voltage was 'real' or induced by the coupling. I found out that if I started on the
500 volt range and then switched to the 250 volt range if the meter pointer stayed in the same relative position I could then switch to the
50 volt range and the meter pointer would still be near the same relative position if the voltage was induced. If the pointer changed positions to follow the 120 VAC when going to the 250 volt scale the voltage was real.
I doubt that the CAT rating requies seperate Amps positions for the leads. Fluke uses special fuses in their meters to get the CAT ratings. They do not have a seperate jack for the ohms settings either which is more likely where the meter would be set. Most of the time the circuit would have to be broken and the meter inserted to measuer amps.
As you say it is impossiable to fully protect everyone from doing somethen forgetful or stupid, but having a $ 300 meter instead of a $ 5 dollar one goes a long ways.
I do have a Fluke test meter that is purty much fool proof up to 600 volts and rated CAT 4. A T1000. It only measuers AC amps by passing a wire through the prongs. It does have a switch for voltage and ohms. I have on purpose set it to ohms and put it across a fuse in a 480 volt AC circuit to see if the fuse is good or bad. No problem to do this.
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