Horn - should it have continuity?

[Cody Forbes]

There is no excuse for not having a scope:

Http://www.parallax.com/Store/Accessories/Tools/tabid/162/ProductID/46/List/0/Default.aspx?SortField=ProductName,ProductName

I've got one and have been using it in a professional environment for  
a few years. It's awesome. It doesn't compare to the old EE scope I  
bought when the nearby Motorolla plant closed down, but for the price  
and 97% of any use I can find for it it is more than worthy.


-Cody (mobile)

On Feb 8, 2010, at 6:58 PM, LL - NY <larrycleung at gmail.com> wrote:

> Addendum.  Since inductive loads create their "reactance" during  
> current
> changes, they tend to show as low resistance loads when tested as a DC
> continuity test. This is one reason why coils are rather difficult  
> to test
> with a simple VOM.  A whole lot easier to test with an O-scope, you  
> know,
> the one that *everyone *has on their workbench (need some form of  
> sarcasm
> smiley). That being said, if you have an "open" test of a horn or  
> coil, then
> you absolutely KNOW it's bad.
>
> LL - NY
>
> On Mon, Feb 8, 2010 at 4:58 PM, <speedracer.mark at gmail.com> wrote:
>
>> Absolutely outstanding!  I now have a perfect picture of what's  
>> going on
>> inside the horn.  Brett was right and I was wrong in calling it a  
>> resistive
>> load.  Lots of intelligence on this list, for sure!
>> Mark Rosenkrantz
>> Sent from my CrackBerry
>>
>> -----Original Message-----
>> From: LL - NY <larrycleung at gmail.com>
>> Date: Mon, 8 Feb 2010 16:39:38
>> To: urq<urq at pacbell.net>
>> Cc: <quattro at audifans.com>
>> Subject: Re: Horn - should it have continuity?
>>
>> Well covered Steve. It's an inductor. And the frequency is in lock  
>> step
>> with
>> the frequency of the horn note. Even an air horn is an inductor if  
>> it's
>> motor compressor driven (such as the Griot's "Italian" horns),  
>> although the
>> ones driven by mechanical compressor (Mack, Kenworth, White, M-B,
>> ElectroDynamics (locomotive)) are not.  Until Piezo-Electric horns  
>> are used
>> (never gonna happen, unless the hybrid people find horn energy  
>> consumption
>> is a major issue) auto horns will always be inductive loads.
>>
>> On Mon, Feb 8, 2010 at 1:51 PM, urq <urq at pacbell.net> wrote:
>>
>>> Most automotive horns are buzzers, with the armature of the buzzer
>>> connected
>>> to a diaphragm to amplify the sound.  A buzzer is similar to a  
>>> relay with
>> a
>>> N.C. contact in series with the coil winding.  When you apply  
>>> power to
>> the
>>> buzzer it pulls the armature of the relay, eventually breaking the
>> circuit,
>>> which de-energizes the relay.  With the relay de-energized the  
>>> armature
>>> returns to rest the switch closes again, which re-energizes the  
>>> coil.
>> This
>>> mechanism is referred to as a relaxation oscillator.
>>>
>>> As Brett noted, a horn is a highly inductive load ... a fact  
>>> accentuated
>> by
>>> the constant opening and closing of the contacts in the horn.
>>>
>>> Steve Buchholz
>>>
>>>
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