Multimeter Auto-Range Function.

[jsi]

First post with a completely newb question, but I gotta ask.  I've had a Harbor Freight manual ranging multimeter for years and it has done the job of measuring the odd voltage here and there.  However, recently I decided to start building electronic do-dads as a hobby so I decided a better multimeter would be a good thing to have.  After much research and conversations with my wallet, I went with the Uni-T 61E.  (I know it wasn't Dave's favorite) 

My question has to do with the auto-range feature.  When I measure the resistance of a resistor it will read .2K Ohm rather than 200 Ohm.  I know both numbers are equal, but one requires a bit of mental math that I thought the multimeter would do for me.  Is this normal?   I don't know if I should be frustrated or not. 

[ataradov]

It is normal. Multimeter characteristics depend on the range. This way of showing a result is an explicit way of telling you what the range was selected for the measurement.

Also, try 100 Ohm and see what happens.

[uncle_bob]

First post with a completely newb question, but I gotta ask.  I've had a Harbor Freight manual ranging multimeter for years and it has done the job of measuring the odd voltage here and there.  However, recently I decided to start building electronic do-dads as a hobby so I decided a better multimeter would be a good thing to have.  After much research and conversations with my wallet, I went with the Uni-T 61E.  (I know it wasn't Dave's favorite) 

My question has to do with the auto-range feature.  When I measure the resistance of a resistor it will read .2K Ohm rather than 200 Ohm.  I know both numbers are equal, but one requires a bit of mental math that I thought the multimeter would do for me.  Is this normal?   I don't know if I should be frustrated or not. 

Hi

A meter with a proper auto-range *should* switch to the range that gives you the best accuracy. All multimeters have some sort of readout that switches part way through a "digit". A 3 1/2 digit meter may read to 1999 or it could read to 4999. If you go "just over" the limit (whatever it is) the reading will suddenly look a bit odd.

Bob

[retiredcaps]

Hmm, according to the UT61E user manual, if measuring a 200 ohm resistor, it should be in the 220 range with a resolution of 0.01 suggesting that the display should read

200.00

[ataradov]

200 is reasonably close to 220, and it might have some hysteresis, so measurements on the edge don't jump all over the place.

That's why I suggested to try 100 Ohm and see what happens. I'm pretty sure it will be displayed as 100.

[uncle_bob]

Hi

Most auto rangers have a built in band that they do not switch in. If you are right at (say) 219 ohms on a 220 ohm range, having it flick back and forth is *very* distracting.

Best bet:

Hook up a variable resistor and see how it tracks the adjustment process.

Bob

[jsi]

Hi

Most auto rangers have a built in band that they do not switch in. If you are right at (say) 219 ohms on a 220 ohm range, having it flick back and forth is *very* distracting.

Best bet:

Hook up a variable resistor and see how it tracks the adjustment process.

Bob

OK I hooked up a pot and the display shows .9K ohms through about .22K ohms when the resistance gets to about .2K it switches over to ohms.     I get it that up around 1K ohms to .9K ohms the decimal point keeps the flicking away and that seems logical. But why it goes all the way down to ~.2K ohms seems odd to me.  Maybe as I get more experienced the logic of it will begin to make sense.

[bitseeker]

It will depend on which direction the value is changing. Most meters will not change on a single value in order to avoid rapidly flipping back and forth between two ranges.

Change the pot value from 100 to 250 ohms observing where it switches ranges, then back from 250 to 100. It'll likely be a different point going down than up. This is the hysteresis in the auto ranging.

Note that on many meters you can manually override the auto ranging.

[Fungus]

My question has to do with the auto-range feature.  When I measure the resistance of a resistor it will read .2K Ohm rather than 200 Ohm.  I know both numbers are equal, but one requires a bit of mental math that I thought the multimeter would do for me.

The is where the 'counts' feature of a multimeter rears its ugly head.

A "200 count" multimeter has to switch ranges when the leading digit is higher than a 2. Usually they switch just below that otherwise they'd never manage to show a reading it you measured a 200 Ohm resistor - they'd constantly be switching ranges instead of displaying a value.

Yours is a "22000 count" meter so a 200 Ohm resistor is close to that limit. I'd really expect it to display 200 Ohms on the finer scale, but... apparently it doesn't.  Nothing you can do.

Is this normal?

Yes.

There's always a value where it will happen. A mega-expensive Fluke 87V is a 6000 count meter so it will do it with a 600 Ohm resistor. etc.

Why do they even do this in the first place? That's another thread.

[Wytnucls]

If you connect your 200 Ohm resistor before selecting the Ohm range, the meter will read 200.00 Ohm, as it will auto range up from a low value first (220 Ohm). If you select the Ohm range before connecting the resistor, it will read 0.2000 kOhm, as it auto ranges down from OL (high value 220 MOhm). That display behavior is due to the auto range hysteresis.

[jsi]

The is where the 'counts' feature of a multimeter rears its ugly head.

A "200 count" multimeter has to switch ranges when the leading digit is higher than a 2. Usually they switch just below that otherwise they'd never manage to show a reading it you measured a 200 Ohm resistor - they'd constantly be switching ranges instead of displaying a value.

Yours is a "22000 count" meter so a 200 Ohm resistor is close to that limit. I'd really expect it to display 200 Ohms on the finer scale, but... apparently it doesn't.  Nothing you can do.

Well that explains it - Thanks

A mega-expensive Fluke 87V is a 6000 count meter so it will do it with a 600 Ohm resistor. etc.

Have you been reading my mind?  I was looking at used 87V's on eBay    Saved me some money you did.

If you connect your 200 Ohm resistor before selecting the Ohm range, the meter will read 200.00 Ohm, as it will auto range up from a low value first (220 Ohm). If you select the Ohm range before connecting the resistor, it will read 0.2000 kOhm, as it auto ranges down from OL (high value 220 MOhm). That display behavior is due to the auto range hysteresis.

I tried what you suggested and it works.  I do wish there was a little logic or way to program the ranges, but oh well. 

[Wytnucls]

You can't have your cake and eat it. Hysteresis is a necessary compromise. If you don't like it, there is always manual ranging.