[time-nuts] Temperature sensors and bridge amps

[Bob Camp]

Hi

The 100 ohm standard for RTD's dates way back. The assumption was that you had it on a *long* run of cable (2 pair / sense leads of course). The insulation leakage was a bigger issue than anything else in the equation. 

Bob


On Nov 12, 2010, at 5:36 AM, Poul-Henning Kamp wrote:

> In message <20101112110627.488cbc8f at vz127.worldserver.net>, "Florian E. Teply" 
> writes:
> 
>> In a bridge circuit, you don't measure resistance directly, but use the
>> voltage that appears across the bridge. So for a 100 ohms element,
>> you'd usually have ten times the current flowing in that branch
>> compared to a 1kohm element.
> 
> This was one of the things that I wondered about:  How large currents
> are used ?
> 
> Can't be too much because that would lead to self-heating...
> 
> Poul-Henning
> 
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.
> 
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