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Bertram31.com General Bulletin Board
Test meters
Posted By: bruce
Date: Monday, 2 May 2005, at 5:41 p.m.
While many know how to use a test meter, here are some basics for those that have them but are tired of using them for a paper weight.
Meters:
A basic meter from radio shack is plenty for what most do either in digital or analog. There are some things you can do with one but not the other.
Digital will give you readings in tenths of a volt which is handy for setting up battery chargers and checking voltages which are critical.
Analog is much better on resistance and continuity testing.The only time I use a digital is for setting up chargers and mine also has a built in graph for checking wave forms and plotting I use for checking FloScan sensors.
Most meters have dials that require you to turn for different functions and voltage limits.
Some meters have a auto ranging function that once the function is set, you don't have to worry about limits on what you are measuring.A basic analog is fine.
Leads:
Good leads are important. If yours comes with cheap ones, throw them out and buy a new set at the shack.
Sharpen the points so you can poke thru wire insulation.
Also get some slip on clips for the end if you need to clip a lead to something.Operation:
Most meters have two to three places to plug the leads into.
Black goes into the com or - one.
Red will go into the +, or volt, ohm.Sometimes there is a third marked for checking current. This is where the red could also go.
Checking voltage:
Plug in leads.
Set the scale to dc voltage or just voltage if the dc and ac dial is the same.
The dial is graduated in different ranges that corespond with the meter face.example, 10, 60, 100, 150 etc.
Set the range high enough so what you measure doesn't peg the meter.
Put the black on a battery negative and the red on the battery positive and you should be reading voltage.
If the meter tries to go backwards then you have the polarity wrong. Check your connections.The ac scale works the same way only there is no polarity problems with ac.
To measure 110vac, set the meter on ac and a high enough scale and put one lead on black and the other on green or white and you should see voltage.
Two measure 220vac, set the scale high enough and measure between red and black for 220 or between green or white to black or red for the 110 legs.
Trouble shooting on voltage.
GPS won't come on.
Measure the red and black to the unit. If you have power, try to turn it on. If the voltage goes down then you have bad connections somewhere that won't handle the load or a bad connections between a fuse and its holder.No power at all.
Find a secondary ground to measure. If you get a good reading, the first ground has the problem. If it stays the same, find a secondary feed. If you get a good reading, the first feed has the problem.AC:
If you read between black and white but nothing on black and green, the ground is bad.
If you read between green and black but not white and black the neutral is bad.If you read between green and white, you have leakage problems or bad connection.
Ohms or continuity:
There is a battery insdie the meter to read these functions. Voltage uses the source to make the meter read. Ohms or cont. uses the internal battery to send out a current thru the wires.Switch the meter to the rx or x1, x10, x100, etc scales.
The best one to use for continuity checks is the x1 scale. Touch the meter leads together and the meter should read. If it doesn't read full scale there is a rotating dial to adjust.
The important thing to remember on the ohms or cont. scale is DO NOT measure VOLTAGE or have voltage present. It will pop the internal fuse if equipt or blow the meter.
Polarity is not important on this check.
Turn battery switch off. Put one lead on the battery negative and one to the engine block.
You should read full scale if adjusted properly.If you do not, then you have resistance, which is a bad connection between the battery ground and engine.
Take the lead off the battery and touch the other engine block. You should also read full scale. If not then there is a bad or missing connection.
You get the idea here. Make sure you take care of the meter battery as you would a flashlite. It can leak and damage the meter insides. As it gets weak, you won't be able to full scale the meter on x1.
The higher scales just represent different resistance values. If you measure 10 on the x1 scale, that is 10 ohms.
If you measure 10 on the x100 scale that is 1000 ohms and on up the line.This is handy if you need to measure specific resistance values on electronics. Very rarly needed in the field though.
You can use the x1 scale to measure fuses.
Touch each lead to the end of the fuse. If it reads full scale, it is good. If it doesn't read anything, its blown.Current:
Using the current scale has cooked more meters. Most meters measure only milliamps or fractional amps in dc. Trying to measure anything more will bake it. Some have a seperate hole for measuring a set higher limit but if you exceed that limit, shake and bake.Dc amps need to be measured with the meter completing the circuit to read. I keep a seperate 0 to 30 dc amp meter for doing just that. I don't use the test meter.
Ac amps requires an attachment if you have a better quality meter or a clamp on amp meter for measuring. It picks up the field and converts it to a reading. You clamp around the black for 110vac or the black or red for 220vac.
These are just some basics. I've tested for voltage in ways I won't repeat here in the risk of getting somebody electrocuted.
Electricity can kill you. Only 6 milliamps will stop the ticker. Be carefull, but no need to be afraid. Electricity is your friend. But if you don't understand leave it up to someone else.
Disclaimer:
Bruce or his kin folk cannot be held responsible for some dumb son a bitch who goes out and fries his ass or burns his boat down. I live in Florida and all my property is in join custody and so the greedy laywers can't touch it in case some relative of a dumb bastard who got fried decides to sue.
Besides, the relative will never make it to court.
(southern legaleze)
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