Ok its been asked what do I have for a multimeter...
Ive mentioned previously I have 4...
but here are the daily workhorses the ones I dont generally lend out to people, not appearing here is my old automotive meter the one thats part tacho/part dwell meter and part multimeter, that one only gets dragged out if im tuning something with points.
so heres my most commonly used electrical diagnostic tools (ATM Got a T4 in the build up stages)
Attachment 5940
the protek 506
the digitech QM-1498
and a fancy test lamp I made myself out of some spare parts as a time killer (long story)
Lets get a bit closer to them...
the 506.
Attachment 5941
It sings it dances it slices it... hang on wrong sales spiel...
this is my workshop meter, its the one I look after and only use at home unless I know Im going out on a job where Im going to need it. its got more tricks up its protective rubber sleve than your average magician and the list looks a little like this
- Autoranging
- ac+dc volts
- Ac+dc amps
- noise level check
- timers
- temperature (one built into the meter and via external K-type thermocouples)
- max, min and average readings
- works as a cro in conjunction with a laptop and the right software
- capacitence check
- diode check
- resistance + continuity checks
- logic probe
- signal generarion
- backlit
and a heap of other little tricks That I cant remember right now.
so in comparison to the one that I look after lets look at the cheapy (which is non adjustable/repairable so I replace it every 12 months or so)
heres the digitech QM-1498
Attachment 5942
its small its one handed and it does most of what needs to be done dealing with auto ranging, resistance, continuity and AC/Dc voltages up to 400v and can do (but Ive never used it) upto 300mA of current measurement. What makes this one shine out above the protek unit is the fact that you can use it one handed and generaly since your looking at where your trying to place the lead tip to get your reading the numbers are right in your face, ditto for resistance checks.
and finally
my testlamp
Attachment 5943
Its got 3 bipolar leds in it a bunch of zenner diodes and some resistors all it does is light up 1, 2 and 3 leds at 6 12 and 24 volts respectively green and red for normal or reverse polarity. The best thing about it is that as its made from totally anologue componentry it doesnt react to a transient voltage that you can get from some faults like earth faults or sensors that have a pulsing voltage output that can screw with some autoranging digital multimeters (the digitech one is a sucker for this).
so how do you use A multimeter?
I'll base this off of the digitech unit as its simple and If someone was to ask me what Id reccomend a DIY bloke to have in his tool kit thats the one I reccomend they have
how this works varies from meter from meter but the principal remains the same. The digitech has 1 four position switch that turns the whole thing off, or selects from volts, resistance and amps. There are also 3 buttons these are
S - Select this changes the type of value you are measuring with in the 3 main functions from Volts AC(also depicted by a straight line with a wavey one under it) to DC (straight line with dashes under it) and on resistance from resitance check to diode check and continutity)
RH- Range hold this one locks the meter into a preselected range value, Using this prevents the delays in getting a read out that can occour or the wierd readings you can get with a voltage thats dancing around.
DH- Data Hold press this and the meter will hold on the display the highest reading it gets on the selected range.
the controls are easily seen here
Attachment 5944
measuing volts, This is the bulk work that multimeters do, simply turn the meter on and set it to measure volts (typically DC in a vehicular application and then press the points of the probes onto what you want to measure and the reading will come up on the LCD screen.
Measuring AMPs, to do this break the circut between the power source and the thing you want to check the amps draw on and then with the meter set on the right amps scale turn on the item or complete the circut, If its able to the meter will give you the number of amps flowing in the circut. Typically when I do this I will pull the fuse that protects the wiring to the thing I want to check and then place the meter probes in the fuse holder in place of the fuse then set the meter on a scale that adequately covers the rating of the fuse.
Measuring resistance, to do this the circut must be dead and in the event of something with multiple current paths (say the parklights) the item you want to check must be isolated from the rest of the circut. Put the meter on the resitance setting, short the probes to confirm the meters zero setting and then apply the probes to both sides of the component and its resistance will be revealed.
Checking continuity. The same rules as checking resistance applies but before you start when you check the zero setting by shorting the probes the meter should beep at you. Then check the component as per the resistance method and if current can flow the meter beeps at you. Be wary of this check though some meters will beep even in the event of very very high resistances and other will beep only for very low resistances.
And thats about it for multimeters.
Oh test lamps...
put one side on a known good earth and then start probing around for your voltagesif youve got a decent voltage with a good supply the bulb lights up, great for checking wiring on rovers but dont use them on sensitive stuff like airbags and engine sensors you need a LED light for that.
