Volt Ohm Meter

[WoodMangler]

I'm trying to test a refrigerator water inlet valve. It should read between 200 and 500 ohm when set at RX10.

My VOM dial says 200, 2K, 20K, 200K, 2M, 20M.

Where do I set my VOM to get RX10?

[JimBill]

Marc,

The X10 scale is typical of analog meters and is the multiplier for the reading. Did the instructions indicate a required resistance value of between 200 and 500 ohms or did it indicate a meter reading of between 200 and 500 when on the X10 scale? The reason I ask is that to read 200 to 500 ohms on the X10 scale, the meter needle will actually be between 20 and 50. By your post I assume that you are using a digital meter with ranges of 200, 2K, etc. To read between 200 and 500 ohms, set the meter range to 2K and take the reading. The meter should indicate between .200 and .500. HTH.

Jim

[WoodMangler]

"The X10 scale is typical of analog meters and is the multiplier for the reading."

So, for an analog meter.. uhhh... crap... I still don't get it :(

"Did the instructions indicate a required resistance value of between 200 and 500 ohms or did it indicate a meter reading of between 200 and 500 when on the X10 scale?"

OK... I'm guessing that the instructions were written with an analog meter in mind because it read "With the meter set at RX10, you should get a reading of between 200 - 500. Any reading significantly lower or higher and you should replace the water inlet valve"

"The reason I ask is that to read 200 to 500 ohms on the X10 scale, the meter needle will actually be between 20 and 50. By your post I assume that you are using a digital meter with ranges of 200, 2K, etc. To read between 200 and 500 ohms, set the meter range to 2K and take the reading. The meter should indicate between .200 and .500. HTH."

OK... Can you explain this to me? I do better if I understand what I'm doing. :) 2K means 2000 to me, so that makes NO sense to me... for a reading of 200-500 set it at 2000???... anyhoo, see what I mean?

Please help this VOM rookie :)

[deathwish2]

>
>OK... Can you explain this to me? I do better if I
>understand what I'm doing. :) 2K means 2000 to me, so that
>makes NO sense to me... for a reading of 200-500 set it at
>2000???... anyhoo, see what I mean?

Yes, set to 2k (2,000) . . . the next step down on your meter is 200, and will not cover the range you need (200-500). If you had a meter with a setting of 500 or 1K, those settings would be a better choice . . . but with that meter, to test that range, '2K' is the only way.

[JimBill]

Marc,

It do get confusing. Okay, here goes. The instructions were most definitely probably written for an analog meter (one with a needle that moves left to right). Your instructions indicate that the meter range be set to RX10. This means that whatever the meter indicates (for an analog meter), that value has to be multiplied by 10 for the true reading (for a meter indication of 20, and the range set to RX10, the actual resistance measured would be 200 ohms). So, in your instance, a range setting of RX10 and a meter indication of between 200-500 would indicate a resistance of between 2000 and 5000 ohms (2k-5k). Since you are not using an analog meter, you have to determine the actual resistance reading needed, per the instructions, and set up your meter accordingly. In this case it looks like between 2000 and 5000 ohms (2Kohms-5Kohms). Your digital meter's ranges are set up to indicate the maximum reading before overload, e.g., for the 2k range, it will read up to 1999 ohms (typically), for the 20k range, it will read up to 19.99 kohms (typically). A range setting of 20k should get you the readings you need. On this range you should get a reading of between 2.00 and 5.00 (2.00 Kohms and 5.00 Kohms). Assuming the valve is a coil type device, a significantly higher reading would indicate an open coil and a significantly lower reading would indicate shorted windings.

Yeehaw!! Ain't this fun!! :7

Jim

[Bob Hobbs]

Golly, there have been some great replies to this already and I can hardly wait to add to the confusion!

I have no idea why the instructions were written the way they were, but what you said was "It should read between 200 and 500 ohm" and we don't really care about the scale because we can figure that out ourselves.

On your digital volt ohm meter, you should expect a reading between 200 and 500 on
the 2K scale.

If you had an analog multimeter (volt-ohm meter), you would set the scale to RX10 and expect a reading of between 20 and 50 (and if you multiplied 20x10 where 20 is the (R)eading or the (R)esistance you would get 200 and 50x10 would be 500)

On analog multimeters, the resistance sclae reads from right to left and the numbers from 0 to 100 are kind of spread out across the scale, after you get past 100 they are all crammed into the last 1/2 inch or so. So the instructions cannot mean for you to read 200 to 500 on ANY scale because you can't, really, so it must mean that 200 to 500 is the actual resistance values.

See an example of an analog scale at:

http://www.multimeterwarehouse.com/YX360TRnf.htm

Here's a better picture where you can actually read the ohms scale at the top of the meter, (and you can read 200 to 500 on the Rx1 scale, but the meter is most accurate in the middle of the scale, so you would set it to Rx10 and read between 20 and 50...)

http://www.altadox.com/specifications/vc3010_specs.htm


--Bob Hobbs

[TDHofstetter]

You've got a good point there, Bob. I'm pretty sure the actual resistance must be something between 200 and 500 ohms - that'd be just about in keeping with the typical current draw on a solenoid of that type & use.

-- Tim --


If you require the approval of others,
You probably don't have your own.

[WoodMangler]

I finally received the new water control valve on Friday. I tested the new valve, and got a reading of 225 ohms. The one I took off the fridge read 175 ohms. The fix-it manual stated the ohms should be 200-500, so I'm hoping I've found/corrected the problem. I'll install the thing next week, then I'll know :)

[Bob Hobbs]

So, what scale did you use to measure it?
A. The bathroom scale
B. Fish scales
C. The scale of C
D. Other _______________

[MorePowerMatt]

With analog and the old style vacuum tube volt meters (VTVMs), there is error inherent in the scale.

Simply, to get an accurate reading, try to select a scale that puts the needle somewhere in the middle of the scale. (from 10:00 to 2:00).

Towards either end of the scale, the readings can be innaccurate.

(This is one of the reasons I appreciate an auto-ranging digital multimeter.)

[TDHofstetter]

Digital is great for lots of things, but one of these days I need to get myself another decent analog, too. There's just no really good way to watch fluctuations with a digital - even a digital with a bargraph across the bottom. Sometimes a needle is the ideal.

Mostly, though, for most purposes, an autoranger is the best way to go. I got almost fanatically fond of my old Beckman probe-style DMM back in the ol' days. The whole DMM was built into one of its own probes. Fully autoranging. I could toss it around my neck while I walked from place to place. I think that was a DM73, but I wouldn't swear to it. Back in them thar days it cost about $75. Seems to me the Taiwanese should have one just about like it available for something like twelve bucks right about now. They tote one out, I'll tote out my wallet. :)

-- Tim --


If you require the approval of others,
You probably don't have your own.

[rrich]

Marc,
The reason that most manuals will suggest using the Rx10 (Resistance reading times Ten) scale is to prevent damage to the component being tested. Typically, a VOM with a "D" cell for the lower resistance scales can put out 10 amps on the Rx1 scale. Using the Rx1 scale on a semiconductor could fry the device being tested.

So here is the way to perform resistance readings using a VOM.

Set the switch to times 100 or 1000.
Keep adjusting the switch until the needle is in the middle 3/4 of the scale.
Read the number and then MULTIPLY the reading by the number after the x. (A reading of 25 on the Rx10 scale is 250 Ohms.)

Hope that helps,
Rich