need help in electrical measurements(ISV)

[Ero Rademer]

Hi!

Konstantin Bogach wrote:
> What I can not understand is why ISV buzzes
> only if I use mA range on DMM?  If I use A or microA
> it does not buzz and DMM shows nothing (.002 as with
> open circuit).

First of all, there are two types of ISVs, the one driven by
a pulsating *voltage* (12V or 0V) and the length of the pulses
defining how far the ISV opens. And the other one, which are
powered by a varying *current* (around 400mA avg?) to control
the valve.

Second. If you use the wrong range on your DMM, the resistance
of the DMM is bigger (microA) or lower (A). The ISV controller
module senses this as an open circuit or a short in the lines
to the valve and ceases operation until you restart the engine.
Thus you do read no current (.002) in either range.

> When I use mA range ISV buzzes and DMM shows 0L. which I
> interpret as infinity.

Rather means "overflow".

"0L" is unusual for a simple off-the-shelf DMM. Normally, when
operated in the wrong range, you will measure 0 (A, mA, uA,
whatever you selected) if the current is too low to display or
an "1.   " if the current is to big to display (over 2.00)
Most cheap DMMs have an 200mA range and measuring 400mA result
in an overflow. If you are measuring the first type of valves,
the current is much higher (for short periods of time) than you
can measure in the 200 mA range. Better measure the *voltage*
across the ISV terminals range on them, the DMM will interpolate
roughly and show between 2 and 7 volts when the ISV is working.

There is no "infinity" when measuring voltages or currents.

If you are a layman when it comes to electrics: Did you have
hooked up your DMM correctly for measuring *current* (in series
with the ISV) and not in parallel to it (for *voltages*)...?

HTH
So long!
Ero.

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