What's with these ohms?

[steviecops]

Hi<br />I've been checking and testing various things on my outboards by following the instructions in the manuals. I know how to read the ohm meter, but I don't understand some of the terminolgy in the manuals.<br /><br />Things like open circuit. What does that mean? Will an open circuit give a high, or low, ohm reading? Infinity reading. What is that? Is it high or low on the ohm scale? And why!!! If a wire/circuit is grounded somewhere, will that give a high, or low reading? <br /><br />I've read various bits and pieces about how it all works, and the only thing I can compare ohms to is frictional loss, as in water flowing through a hose. (Firemans training ;o) What I can't work out is whether the more friction, ie, resistance, = higher ohms or lower. <br /><br />If anyone has a really simple explaination of all this, I'd appreciate it. This is keeping me awake at night!!!<br /><br />Thanks<br />Steve

 

[rodbolt]

Re: What's with these ohms?

hello<br /> if it was that simple everyone will do it. think of voltage as water pressure. current is water volume. resistance is the restriction to current.<br /> infinity is just that. infinite resistance. hold the two probes 1 foot apart and you have infinite resistance, also known as an open circuit.<br /> as for your scale settings the meter is most accurate in the mid point of meter movement. most digital meters with an auto ( auto is my friend) function change scales automatically.<br /> what kind of ohm meter are you using.<br /> any othe questions ?<br /> good luck and keep posting

 

[JB]

Re: What's with these ohms?

OHM. The amount of electrical resistance that will allow 1 amp of current when 1 volt is applied to the circuit. More ohms, less amps.<br /><br />In the infamous Ohm's Law, which expresses the relationships among the voltage applied to a circuit, the resistance of the circuit and the amount of current flow. <br /><br />R (resistance in Ohms)= E(voltage applied)/I(resulting current flow in Amps)<br /><br />R=E/I; E=IR, and I=E/R<br /><br />Ohms on the range are a whole different topic.

 

[steviecops]

Re: What's with these ohms?

Thanks for the explainations.<br /><br />What do these readings actually look like on the scale? Is an infinate reading/open circuit, a high number, or a low one?<br /><br />I'm using an analog meter, but I've used digital too. Strange thing to me though is, the digital starts on a low number, ie, 0 or 1, and goes up as you touch the probes on whatever you are testing. Yet the analog starts off the scale, and comes down as you touch the probes. Guess I just answered my first question there! An infinite reading is off the scale right? ie, a high number. Is that because there is no resistance, or because there is absolute resistance?<br /><br />Thanks again. I will get there in the end.<br />Steve

 

[ED21]

Re: What's with these ohms?

With an analog meter infinite resistance is off the scale. No current can flow. An open circuit.<br /><br />O ohms indicates a closed circuit w/ no resistance like when you touch the probes together. Analog meters usually need to be zeroed. They have a small wheel to adjust.

 

[steviecops]

Re: What's with these ohms?

Thanks Ed. I think I've finally got it! So closed curcuit is that other term I've read about. Continuity!<br /><br />Great stuff.<br />Thanks<br />Steve

 

[rodbolt]

Re: What's with these ohms?

see how simple it really is.<br /> man I'm gonna be out of a job. another victim of "outsourcing" <br /> good luck and ask if ya got any more questions

 

[smudge]

Re: What's with these ohms?

As an electrician I can assure that the advice given is all correct.<br /><br />An Open Circuit = Infinity on the ohm meter - or at least a very high resistance.<br /><br />A Closed Circuit = Zero ohms or very close to it.<br /><br />You will usually get some resistance just in the leads themselves that may be half an ohm. If your multimeter is a flash one it may have an REL button (relative) so you can short the leads together, press the REL button and it zeros the display...

 

[swist]

Re: What's with these ohms?

Another bit of advice - watch out for false shorts - you saw Ohm's law in an earlier post. A device drawing a lot of current at relatively low voltage will have very low resistance - it may in fact look like a short unless you use a very accurate low range scale. Also note that some devices like light bulbs and motors don't present much resistance until they are running. Again, you can mistakenly assume they are shorted. And lastly the same thing can happen if you measure some devices which are normally AC driven (transformers, ballasts, etc) - an ohmmeter usually measures DC resistance which again will read very low on an AC device and you may assume a short.

 

[steviecops]

Re: What's with these ohms?

Thanks again guys. Your help is much appreciated.<br /><br />Steve