Subject:
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Re: Motors & handyboard
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Mon, 17 Feb 1997 15:17:39 GMT
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Original-From:
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ED Spike <SPIKE@/spamcake/EESTAFF.watstar.uwaterloo.ca>
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Viewed:
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1568 times
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> On Fri, 14 Feb 1997, MAR ERICSON wrote:
> > > Yesterday I tried to run a motor out of the HB. First I tried how much =
> > > current it needed with a multimeter and a 5V power source ... The result =
> > > 75mA.=20
What is 20?
> > EE Question:
> > How do you use a multimeter to measure the current?
> > I was told that you need a current probe to do this kind of thing.
> > ??
Current meters have an internal resistance.
The lower the current range the larger the resistance --- even with
digital current meters.
Some typical values For example:
Digital Analogue
Current Range R_meter R_meter
200 uA 1000 ohms
1 mA - 100 ohms
2 mA 100 ohms
5 mA - 20 ohms
20 mA 10 ohms
50 mA - 2 ohms
200 mA 1 ohms
2 A 0.1 ohms
I'm not sure if this relates to your problem.
There may be a significant voltage drop across the current resistance
with a low resistance of the motor if the currentmeter internal
resistance is large enough.
---------------------------------------------------------------------
Ed Spike,
E&CE Department, University of Waterloo. E2-3357 *
Communication and Microwave Area Laboratory Instructor. *
(519)888-4567, x3716, FAX: (519)746-3077 *____/
URL: http://www.ece.uwaterloo.ca/~spike * / CQ
*
IEEE Student Branch Computer Chapter Advisor, *
Robot and MicroMouse Competition Co-ordinator,
Sharing, DYB, Be prepared,
Challenge, Service.
Amateur Radio - VE3TCK, Enjoyment, Fun.
Asahi Judo Club, _0_/
Scouts Canada Crew Advisor, U. of Waterloo, / |
Scouts Canada Cub Leader, 17th Waterloo, | _
Waterloo Minor Soccer Association Coach. _/ |_ O___/__| Ippon
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Message is in Reply To:
 | | Re: Motors & handyboard
|
| To measure current with an multimeter or ammeter (volt/ohm/etc.. meter) you must break the circuit at some point and put the meter in series with the circuit thus gapping the break. ie) +-----(+) METER (-)------+ | | | | (+) | POWER | (-) | | | | | (...) (27 years ago, 15-Feb-97, to lugnet.robotics.handyboard)
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