Extech Milliohm Meter Question

[bostonman]

When I use my milliohm meter in the 2k range, and measure a 205 ohm resistor, the display shows .205

This implies the resistor is 205m ohms. The other settings seem fine, so I'm wondering why the odd measurement reading.

[tooki]

You didn’t specify the model number (always a good idea), but if it’s the Extech 380580 sold today, then from looking at the manual, I see that it can show an “m” annunciator on the display for “milli”. Is it conceivable that it is displaying a “k” for “kilo” that you’ve overlooked? Because 205 ohms is 0.205 kilohms.

[bostonman]

Sorry, I didn't think about the model, it's: 380560

[tooki]

The datasheet and manual for it both explain it in the resolution specs, where for the 2K range, the resolution is shown as “0.001kΩ”.

[bostonman]

Oh… okay. The resolution specs in meters tend to confuse me. I thought that meant how far off it may be - didn’t think the decimal place would be moved

[tooki]

Nope, “how far off” would be a tolerance.

“Resolution” means “the smallest unit that can be resolved” (i.e. the smallest step that can be shown; analogous to the concept of the LSB (least significant bit) in binary).

It is VERY common for the decimal point to move around, because ranging is typically doing just that: multiplying or dividing the input by a factor of 10.

One of the oldest ERVblog videos is about multimeter ranges, counts, specs, etc. Take a look!

[bostonman]

It's funny, I've never paid attention to ranging or resolution.

When the meter flips digits, I just go with it without thinking.

This meter is the first one that has confused me because I'm looking at .205, so in my head it's 0.205 ohms and not 205 ohms. I'm going to play with the 2k setting a bit more using a resistor box.

[bostonman]

I spent a few minutes flipping a decade box (resistor box) while changing scales.

I'm still a bit confused why the decimal place needs to be before the 205. When looking at the display, the first thing that pops in my head is 0.205 ohms, but I can't wrap my mind around why this is actually 205.

By the way, I watched the video and the 3 1/2 digit thing makes more sense now, but I don't see how applies to my situation.

[ejeffrey]

Can you just post a photo of what you are talking about?  Otherwise there is really no point to asking.

[bdunham7]

I'm still a bit confused why the decimal place needs to be before the 205. When looking at the display, the first thing that pops in my head is 0.205 ohms, but I can't wrap my mind around why this is actually 205.

It doesn't.  They could have called it the 2000 ohm range and omitted the decimal point.  But they didn't, it is the 2kohm range, so you get .205 kohms. 

If I had a scale with a 2kg range and it read .205 kg, would you still be confused?

[bostonman]

Well, yes, a scale showing .205k makes more sense.

In your example, the 2k ohm range doesn't mean anything. It can be 200k and the display could read .205k, however, the unit doesn't display 'k' leaving it to the viewer/user to assume there is a 'k' in there.

In the current configuration (without a 'k'), to me, it somewhat implies it's 0.205 * 2k or 410ohms.

I understand what you're saying, it just seems like a really odd way to show a precise measurement by not telling the viewer a 'k' is in there.

[bdunham7]

I understand what you're saying, it just seems like a really odd way to show a precise measurement by not telling the viewer a 'k' is in there.

It's a manual ranging meter with a rather primitive display.  You're supposed to know what range it is in.

In the current configuration (without a 'k'), to me, it somewhat implies it's 0.205 * 2k or 410ohms.

Whatever your thought process was that got you to that point, figure out what it was and don't think like that in the future.  The full-scale and the units of the range are two different things.

[tooki]

In your example, the 2k ohm range doesn't mean anything. It can be 200k and the display could read .205k, however, the unit doesn't display 'k' leaving it to the viewer/user to assume there is a 'k' in there.

In the current configuration (without a 'k'), to me, it somewhat implies it's 0.205 * 2k or 410ohms.

I understand what you're saying, it just seems like a really odd way to show a precise measurement by not telling the viewer a 'k' is in there.

But they DO tell you: it’s the 2K range. See that K? Yes, that one. That’s your K telling you that the unit of the numbers on the display is kOhms.

I’ll be honest, I also would prefer it being a “2000 Ohm” range. I have some multimeter that works like yours and it’s not my preferred presentation. But neither is it confusing. If you’re doing electronics, you have to get yourself completely comfortable with the prefixes, like understanding that a 0.1 μF capacitor is the same as a 100nF one. This is the same idea.

[bostonman]

I’ll be honest, I also would prefer it being a “2000 Ohm” range. I have some multimeter that works like yours and it’s not my preferred presentation.

I appreciate you acknowledging how it can be a bit confusing and a less desirable method.

like understanding that a 0.1 μF capacitor is the same as a 100nF one.

Something funny, years ago I didn't have a problem with things like this and (as an example) using a current probe on a scope that measures V/A and then converting say 2V to the current (in amps). At some point I expanded my math when I returned to school and suddenly using algebra to solve equations caused me to overthink the most basic stuff.

Now I look at (per your example) a 100nF capacitor on Digikey and say, wait, I'm looking for a 0.1uF, am I going right or left with the decimal point because I'm thinking in terms of exponents rather than the tribal math I used when I knew less. Before I'd just somehow know to multiply A and B, or divide A by B, or whatever without thinking twice. Then once I began thinking about how to actually do it, I began confusing myself.

Now I've grown use to digital meters where WYSIWYG meaning, when the meter reads 0.205, it's 0.205V or ohms (assuming my Fluke meters went that low).