[Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Colin Law
On 4 October 2013 20:28, Jan Kandziora wrote: > [snip] > In addition, > measuring low temperatures with parasite power is bad, as it heats the > sensor and thus, gives you slightly wrong temperature values. I don't understand why this is worse when measuring low temperatures than high. If measu

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Colin Reese
Without comment on the details of this situation, that is not how convection and conduction work. Convection is typically described by Newton's law of cooling: q=hA(T-Tamb) Conductions is q=k*dT/dx ~k (Tsurf-Tamb)/dx Thus the heat transfer rate depends explicitly on the difference between tempe

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Colin Law
On 5 October 2013 09:31, Colin Reese wrote: > Without comment on the details of this situation, that is not how > convection and conduction work. > > Convection is typically described by Newton's law of cooling: q=hA(T-Tamb) > Conductions is q=k*dT/dx ~k (Tsurf-Tamb)/dx > > Thus the heat transfer

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Colin Reese
I'm not sure I caught all of that, but at steady-state: Pdissipated = qconduction + qconvection = k (Tdevice - Tamb)/ (thickness of boundary layer) + hA(Tdevice - Tamb) If you are dissipating some amount of power, the device will heat to a temperature above ambient so that the equa

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Mick Sulley
I agree with what has been said, but a further question - the discussion refers specifically to parasitic power, does the same not apply to powered networks? I had always assumed that it did, just that powered was faster, I am wrong here? On 05/10/13 09:31, Colin Reese wrote: > Without commen

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Håkan Elmqvist
Dont forget Planck's law H H Skickat från min Samsung MobilColin Reese skrev:I'm not sure I caught all of that, but at steady-state: Pdissipated = qconduction + qconvection = k (Tdevice - Tamb)/ (thickness of boundary layer) + hA(Tdevice - Tamb) If you are dissipating some amo

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Jan Kandziora
Am 05.10.2013 11:01, schrieb Mick Sulley: > I agree with what has been said, but a further question - the discussion > refers specifically to parasitic power, does the same not apply to > powered networks? I had always assumed that it did, just that powered > was faster, I am wrong here? > It'

Re: [Owfs-developers] Self heating and parasitic power [was Failing DS1820]

2013-10-05 Thread Colin Reese
I assume you are referring to radiation. At this temperature that is not an issue. You need to get pretty darn hot for it to contribute. Colin > On Oct 5, 2013, at 11:31, Håkan Elmqvist wrote: > > Dont forget Planck's law > H > > H > > > > Skickat från min Samsung Mobil > > Colin Reese