How do I check a gauge for ohm's

As the ***le said, I'm talking about a Gas gauge,I have never done this before, any help would be much appreciated....Thanks

 

I take the wire and hold both ends, one end in each hand, sit cross legged on the floor, close my eyes and repeat:
ohm.....ohm....ohm....ohm

You can use a ohm meter it will test the resistance of the wire. you can get one at most any hardware store. get the digital kind much easier to read than the sweeping needle

Just jokes,
Godspeed
MrC.

 

What exactly do you want to check ?
If you want to bench test a gauge you'll need a power supply and a POT or the sender and a multi meter.
If you want to check the sender you need a multi meter.
Trying to match them up ?

 

Let's say you have a 12 volt system and a 30-0 OHM sender. If you put a full 12 volts across the guage terminals it will read "full", if you place a 15 OHM resistor inline with one of the terminals it will read "1/2 full".

To test the sender just place an OHM meter across the terminals and lift the float slowly. It will read 30 OHMs when the float is all the way up and 0 OHMs when the float is all the way down.

 

i think he's looking to replace. alot of aftermarket gauge co's tell you to check this to match up the new gauge to your particular needs

 

Well I can't read minds , and I could but don't want to write a whole book..

 

Sorry guys, more info needed ?
I have a gas guage that I need to know what ohm it is so I can try to match up the gas tank float with...If you need more info. please ask....Thanks

 

It's easy, watch the video and read - http://www.google.com/search?q=how+to+use+an+ohmmeter&ie=UTF-8&oe=UTF-8&hl=en&client=safari

 

Ok you need a power source that matches the gauge - 12 volt or 6 volt.
You need a Potentiometer http://en.m.wikipedia.org/wiki/Potentiometer
You need a multi meter .
You need some jumper wire and alligator clips.
One stop shopping at radio shack

The Pot will simulate the full empty / sender for your test.

Determine open and closed direction on the POT. Use the multi meter on ohms setting across the pot as you turn the dial. Make some reference marks on the pot when the meter hits O 30-60-90-120 ohms.
Connect one wire to both sides of the pot,
Now connect - depending on the gauge and battery (important) connect the correct side of the correct battery to the correct side of the gauge.
Connect one wire off the pot to the other side of the battery , and the other to the gauge.
For 12 volt it would be battery pos to gauge, battery negative to pot then to gauge.

Ok turn the POT and your gauge will move, note the readings and your marks.

I ***ure you OT took longer to type this on my phone than it takes to do it.

 

What kind of gauge is it? Every manufacturer has their own standard and they do not change for decades. Ford and Chrysler products were the same for years. GM were all the same. Aftermarket gauges usually one or the other.

Do a Google search for aftermarket gauges, they will have a list of different makes of cars and what they take.

 

You might look closely at the back of the guage if its aftermerket, some of them have the ohm range printed or stamped on the housing. JJ

 

And just because a gauge is from a vehicle with a 12-volt system, it does not necessarily mean that the gauge operated on 12 volts. A lot of vehicles have a voltage reducer of some kind or another. So I'd recommend NOT just hooking 12 volts to the gauge.

For example, a late 50's Chrysler has a bifurcated strip of metal wrapped with nichrome wire. When the wire heats up, the strip curls and opens the circuit. You can see this very obvious voltage fluctuation on the fuel gauge.

The way I check what a gauge needs for a sending unit is with a five watt, 50 ohm wire wound rheostat, but I may be heading into territory here that will just add confusion, so I won't go there.

 

Well the usual ********ters chimed in with a bit of nonsense to mess with your mind a bit but here goes:
Get a multimeter. Set it to ohms 0 to 100 being the ideal setting and connect one lead to the connector for the wire to the gauge and one to the ground terminal or body shell of it if there is no ground terminal. Then move the lever of the float and watch the ohm meter. It should read across the span of what ever it is rated for. Usually either 0 to 90 or 0 to 30 . that is all there is to it.

The gauge and the sender have to have the same ratings and be compatible is the other thing.

 

I chimed in to help the guy out, certainly hope you aren't including me in the usual bunch of ********ers.

Unless I complety misunderstood the question,
1. he has no sender to check.
2. Needs to procure the correct sender to match the gauge he does have.
3.Yet he has no idea of what ohms the gauge is designed to read.

Since you've explained how to read the sender that he doesn't have, how about you tell him how to check what his gauge is designed to read. You know you can help us all get our minds right since the usual bunch of ********ers messed them up.

BTW, Ebbsspeed sheds further light on how important it is to have the proper voltage supply for the gauge.
The method I described would for any gauge that uses variable resistance. You can get the correct senders for oil pressure, water temp from napa if you know the operating ohms range of the gauge.

 

But, remember, NEVER apply an ohmmeter to anything in a circuit with power on it. It can smoke your meter. Forget the battery. The ohmmeter has its own battery.

 

Old Buzzard - that's a good 'Rule of Thumb' for general purpose. There are exceptions, but unless you know your equipment, you run the risk of letting the smoke out of what used to be a good meter.

My rule of thumb for resistance checking on an unfamiliar system? Always check for voltage first. If you get a '0' indication, then it's safe on all to check for resistance (horseshoes).

 

absolutely correct ! That's exactly why the ohm meter goes on the POT and then the POT goes into the circuit.

 

shin bones connected to the knee bone,
knee bones connected to the thigh bone...uh...wait....wrong thread sorry

 

And this is not a live circuit????? It has a battery in it!!! You make your settings, disconnect the power, THEN make your resistance readings. Across every resistance is a voltage drop. An ohmmeter cannot read voltage. A small amount of voltage can smoke an ohmmeter.

 

Yes of course that's a live circuit, but there's no meter involved with the battery.

 

Yes, but here we don't know that they do. We don't know what sort of meter it is. Unless the meter can account for its own battery there is no accuracy and the supply is broken into small enough parts so that it doesn't take much to screw it up.

 

The BATTERY VOLTAGE & CURRENT is distributed along the circuit. Every time you measure across a resistance you are measuring across a part of the battery voltage.

 

I hear you, go back and read the post. There is no none NADA zip nothing to do with a meter or measuring of anything specifically ohms once the battery is connected.

You are missing that part

 

I gotta laugh at those who can't or won't pay attention....

post 9, he checks the pot OUT OF CIRCUIT with the ohmmeter,
THEN he wires it into the circuit....
no voltage used while checking and marking the pot.

this **** happens every time something technical is discussed.....

 

What year and car model sender are you trying to check?

 

Yeah, maybe I got a bit carried away, but all I did in the beginning as toss out a caution about sticking an ohmmeter in a live circuit.

Sorry 'bout that. I guess I'll have to be more careful about getting on here on a day when I've been up since 3 AM. OldBuzzardness must be catching up with me worse than I thought.

 

Rest up buzzard.

 

OK..I have been told Buick or Olds 1949??? Gauge cluster

 

GM sender pre 65 0-30 ohms. Wasn't that easy?

If you want to test it out you can use your ohm meter, a rheostat or potentiometer, and a 6 volt battery, or even a 9 volt transistor radio battery.

 

So many answers, so much confusion, so many people telling how to measure a sending unit that you don't have. Some people calling others ********ters when they, themselves, haven't read or do not understand what the OP is asking.

Not bragging, but I'm really glad that I have a thorough understanding of how electrical circuits and devices operate. It seems like every time there is a question here about a starting circuit, or an ignition circuit, or wiring a generator or alternator, or gauges, or a bilateral transverse low-frequency oscillator, or anything else pertaining to the flow of electrons, then anyone that has ever put a battery in a flashlight responds because they think they have the right answer. If you are not absolutely certain about how to wire something, or measure voltage, resistance, or current in a circuit, then don't post an answer because it will most likely confuse the issue. When you signed up to this forum, you should have read Ryan's "Read This First" post, where guideline #1 says "1. If in doubt, don't post it." Yes, it is the VERY FIRST guideline. Here's the link if you didn't follow the rules and read it:

http://www.jalopyjournal.com/forum/showthread.php?t=44274

To the OP: Ship me the gauge. I'll tell you, within half an ohm, what you need for both an empty and a full reading on that gauge. I will buy you the appropriate sending unit, and I will ship it all back to you. Free. From Shawnee, Kansas, USA to Bowmanville, Ontario, Canada. The one condition I will place on the offer is that you must have a moderator close or delete this post, so that the confusion is not perpetuated.