electrolyte challenge: orange juice vs sport drink

[ktps]

I have data from my experiment, but don't really know what to do with it. I followed the directions in the Electrolyte Challenge: Orange Juice vs Sports Drink experiment to make a conductance sensor and a conductance measuring circuit. My multimeter has these options for DC: 2000m, 20, 200, and 600. It doesn't have 200m like the one described in the experiment. I measured tap water, juice, milk and sports drinks using the 20V setting. I got values ranging from 9.64 to 9.67. I tried to measure the distilled water on the 2000m setting (since I don't have 200m), but got an error value. I tried it on 20V and got an average of 9.37. I thought it should be close to zero. I thought the distilled water should be different than the other liquids.....?
My second question is what do I do with my data?
The experiment gives the equation G = I/V (conductance - current (amps) / voltage.) So if I use the reading I got on the multimeter for gatorade, 9.69, and divide it by 9 (I used a 9 volt battery) I get a value of 1.077. But the experiment says to convert milliamps to amps first by dividing by 1,000. So the value would be .001077. Do I really have to do that?
That number doesn't really mean anything to me. But I think my data shows that there isn't much difference in electrolytes between sports drinks and tap water, juice or milk.
So,
- why don't I get close to zero for distilled water?
- Do I have to divide by 1000?
- Did I do the equation right?
Thanks!

[rmarz]

ktps - There is some confusion on what your multimeter settings are. You should be using DC current ranges, usually 200 milliamps DC (mADC) for most of your conductance readings. There is no reason to use of a voltage range in this experiment. If you did, any conductive liquid would only measure battery voltage (which it appears you did, therefore you got values of around 9 volts). You said your meter didn't have a 200 milliamp range, but then you listed all the ranges and it included a '200' range.

Your readings will be in the range of microamps for distilled water (go ahead and use the lowest range) up to near 100 milliamps for the highly ionized drinks.

Yes, the equation is correct, and you have to convert your milliamp readings to amperes by dividing by 1,000.

Your readings appear to be the incorrect voltage readings (not current), so your results are incorrect.

Read the instructions for your multimeter to get a better sense of how to set the ranges and to better understand what you are measuring (voltage or current).

Rick Marz

[ktps]

Hi,
Thanks for the response.I tried to attach a photo of my multimeter and the experiment set-up, but couldn't. My meter has 3 settings: DC Volts, AC Volts, and Resistance. The DC Volts section (has a V symbol with a straight line over it) has these markings: 2000m, 20, 200, 600. This is the section I used. There is an AC Volts section (a V with a squiggly line over it) that has these markings: 500 and 200. And there is a Resistance section (it has an omega symbol) that has these markings: 200, 2000, 20k, 200k and 2000k. That is all there is on the multimeter. The directions said to use the direct current settings and I used the DC Volts section thinking that's what that was. Should I have used one of the other two sections?
Thanks

[rmarz]

ktps - Interesting description of your multimeter. If you can't get a photo of it, can you get the make/model number off it? Does it have a digital display? I've never seen a multimeter that only did AC/DC voltage and resistance but had no current range. Is there a separate socket for the test lead for 'current'. Until we understand your ability to measure DC current, we can't go very far with what we know.

Rick Marz

[ktps]

Hi,
I have a Gardner Bender GDT-311 multi-meter. Here is a link to an image of the multi-meter: http://site.unbeatablesale.com/img233/jnsn30016.gift
Thanks!

[rmarz]

ktps - Well, seeing is believing. Although this company seems to build tools for the electrical trade, you would think they would have included DC current measuring capability. In short, this experiment can't be done as described with this meter. You can find others even below $10 that will do it. Harbor Frieght usually has an acceptable unit for less than that, on sale. Often you can get one free from them with a magazine advertisement coupon. Time to regroup.

Rick Marz

[ktps]

Hi, bummer Ok, so the multi-meter I have only measures DC voltage and I need to have one that measures DC current? I think I did all the other steps right. So if I get a value close to zero for the distilled water and close to 100 for the gatorade, then everything is probably ok? If I got 100 for gatorade, I would divide it by 1000 to convert it to amp and divide by 9 volts? So conductance = .1 divided by 9 = .011? And the higher the conductance the more electrolytes there are in the drink?
Thanks

[rmarz]

ktps - You stated it all correctly. In fact, those should be close to the readings you will get. Perhaps you can borrow another meter from a friend or from your school. Keep us posted. I think you are on the way.

Rick Marz

[ktps]

Ok, thanks and thank you very much for all your help!!

[ktps]

Hi,
I bought a new multi-meter for $10 dollar that measures current and redid the experiment. I think everything went fine this time. I got different values this time so I'm sure I was measuring current and not voltage. When I measured powerade I got a value of 37.8, orange juice, 45.6 and milk, 61.5. But I only got a reading of 1.1 for tap water and I thought I would have gotten a higher value. And the distilled water got a reading of 34.2 and I thought it should have been closer to zero. I did the distilled water on the 200 microamps setting and all the other ones on the 200 milliamps setting. After I divide by 1,000,000 for the distilled water and by 1000 for the rest, the distilled water will have a smaller number so maybe that makes sense but I still thought the tap water would be higher?

[kgudger]

Hi:

Yes, your distilled water value is much lower than the rest, so that's good. Maybe your tap water is very low in minerals? It's certainly lower than the sports drinks, so getting a lower number is not surprising. Sounds like you've done a good job.

Keith

[ktps]

Thank you very much and thank you everyone for your help!

[rmarz]

ktps - Glad to hear it all seems to be working as planned.

Rick Marz