Meter testing for ecm work

[Ludis Langens]

Bruce Plecan wrote:
> 
> Is there a way to test to find out if a analogy (needle) type meter has
> enough impedance to work with say an O2 sensor?.

First off, it must have a power source (and not just for the ohms
setting.)  If it can measure volts without a battery installed or
without being plugged into an AC outlet, it won't work.

Its quite likely that better quality meters will specify their input
impedance.  This isn't an idle marketing boast.  High voltage probes
(multi kilovolt) rely on a specific meter impedance - the probe is
probably just a 10M resistor that uses the meter's 1M input impedance to
form a simple voltage divider.

If you meter doesn't have a specification, here's how to check it:  Get
a small battery (D cell, AA cell, etc.) and a 1M resistor.  First, use
the meter to measure the battery voltage directly.  Then measure it with
the 1M resistor in series (make sure you don't touch the resistor <->
meter node of the circuit).  If the meter has a 1M impedance, the second
reading should be about half of the first.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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