Low range voltmeter

I am finding it a little tricky to find a 12v voltmeter (as in the main operating voltage) that measures from 0v to about 2.0 or 3.0v (preferably digital display)

I am looking to accurately measure the AFR.

Anyone know of a supplier? Nigel?

Thanks.

The idea for the zener diode was to allow the meter to be powered up off the 12V in the car rather than the 9V (or whatever) battery inside a multimeter. You'll only need to do this if you are running around for weeks and weeks with a meter in the car. For a 9V meter, a 5V zener diode would be about right. This is a bit of a bodge, but it would hold the voltage between about seven and nine volts to power the meter. If you buy such a thing from RS you can also get an applications data sheet that will explain how to use it.

Incidentally I bought a cheapo multimeter from maplins recently (£4.99 in a sale) just to have one in the beemer (18 year old electrics not 100% reliable). Out of curiosity I checked it against a properly calibrated instrument and it was fine.

cheers

Thanks for the amount of input guys!

I have looked at maplin - no spec as yet for the analyser...

Doive wrote: Oh dear, what have I let myself in for??

He he he!

Shows what a pillock I am, talking right out of my bottom:

http://www.picotech.com/auto/lambda_sensor.html

I would assume from this that my multimeter (machine mart - £40) would be 10k ohn device, is this an industry or other standard for multimeters?

Doive (here we go!), on page 4 there is a caution statement about zirconium sensors (how would I tell?) and 'jumping' the sensors leads (what and how is this?)

Sorry to be a pain in  the backside!!

Cheers

I tend to use Flukes, very accurate, but I think they run out at around £150 - £250, depending on what spec you want, and what calibration cert etc.

As for the 9v PP3 battery, they last about a year.

I also use a textronics hand held scope, which includes a very accurate voltmeter, but now your talking around £1000, great for setting sensors up though.

You do tend to get what you pay for, and to be honest £15 - £20 should get you a cracker for occasional use.

I dont like that pico stuff, I have tried it, its update time is too slow for me, and I have known people to damage their laptops with it, albeit by their own stupidity, but its still an expensive repair.

Yes thats the stuff, picoscope, and the rest of the instruments they do.

Its dam good software, but as its running on a computer its update is quite slow, and of course, the interfacing problems.

But it is cheap, so use it carefully and you could get some good results.

Hi Sleeper and all,

I assume you are trying to monitor the oxygen sensor signal on your car, and your car is fitted with a Zirconia sensor. 

The first thing that you should be aware of is that the sensor should very rarely show a steady voltage. A zirconia sensor should switch between about .2 and .8 volts when the mixture is correct. This switching should happen at a rate of about 1 hertz (once per second), very often much quicker. No cheap multimeter will be capable of displaying this, they are much too slow. The Pico is a great tool to use for something like this as it is so fast. The only reason it is so cheap is that you use a lappy or desktop iin place of the usual hardware you would need to buy in a dedicated scope.

The O2 sensor (oxygen sensor) measures the amount of oxygen in the exhaust gases. This is directly related to the mixture (air/fuel) being burned in the combustion chamber. The min and max signal voltage as well as the frequency of the switching rate are all very important to the ECM (engine control module) as it uses this to choose the level of fueling required by the engine. 

This is quite a complex subject (and i am just in from the pub :) ), but if you have any specific questions, please ask and I will be happy to try and answer them.

regards

Alan