Re: Circuit to output difference in temperature between two thermistors

On a sunny day (Sat, 10 Jan 2009 14:59:00 -0500) it happened Phil Hobbs
<pcdhSpamMeSenseless@xxxxxxxxxxxxxxxxxx> wrote in
<4968FE04.1090705@xxxxxxxxxxxxxxxxxx>:

Jan Panteltje wrote:
On a sunny day (Sat, 10 Jan 2009 13:10:53 -0500) it happened Phil Hobbs
<pcdhSpamMeSenseless@xxxxxxxxxxxxxxxxxx> wrote in
<4968E4AD.9080907@xxxxxxxxxxxxxxxxxx>:

IC temperature sensors measure the temperature of their leads rather
than of the air, because copper's alpha is 300-400 W/m/K as opposed to
0.025 or so for air. Wire has to be very long and skinny to overcome a
factor of 15000 in thermal conductivity. They also have poor initial
accuracy compared with thermistors. The nonlinearity of thermistors is
inconvenient, but their -3%/K tempcos, low noise, very fine leads, and
excellent calibrations make them unbeatably sensitive for temperature
control. Fine line flex circuits in very thin copper, with in-plane
serpentine bends, make the best leads.

Cheers,

Phil Hobbs

But there are ICs with digital output, making any cable length irrelevant.
Anyways, a PIC next to a LM135 does the same, can send the temp via RS232,
or any other protocol, if must be.
It all depends on the application.
The IC wires may well be in the same area that needs to be measured.

If your application is squishy enough, they can work fine. For precision
temperature stabilization--even at a single temperature--they're junk.

Cheers,

Phil Hobbs

I see you are a person of extremes :-)
I just wonder about the difference between 'stabilization' and 'stabilisation'.
My spell checker insists it is 'stabilisation'.

I do not like thermistors, those are not linear.
I like linear for most purposes.


.

Relevant Pages

  • Re: Circuit to output difference in temperature between two thermistors
    ... or so for air. ... Wire has to be very long and skinny to overcome a ... accuracy compared with thermistors. ... serpentine bends, make the best leads. ...
    (sci.electronics.design)
  • 2 Part Electrical question...
    ... This is a long post but I'm young and dumb and you guys are smarter and I'm bouncing ideas off. ... I'd like the outlet in the bottom of the bookcase because it'll house the router and modem and back-up drives etc. Run one power bar that powers one computer and all of it's peripherals and use the other receptacle to power the other computer and it's peripherals. ... The only accessible path I can run the wire where I have 60 feet of access to snake it the length of my house has both an air-return and an 8 x 16 x duct work in the way. ... The air return pathway is just sheet metal nailed to floor joists so I'm thinking I can drill thru the joists and snake my wire thru the air return. ...
    (alt.home.repair)
  • Re: 2 Part Electrical question...
    ... Both desks will house computer workstations ie ... Should I look at 20 amps if a single circuit? ... The only accessible path I can run the wire where I ... The duct is actually directly below the air return pathway running ...
    (alt.home.repair)
  • Re: Suspend those pesky physics laws!
    ... I have an air cylinder, 1.5" x 4" stroke, that pushes a crank on a shaft ... between the gears in a grove cut in the face of each gear. ... feed wire 3" per stroke. ...
    (rec.crafts.metalworking)
  • Re: Next project; deja vu
    ... This is now done with an air cylinder pushing one-way clutched rollers. ... Imagine a DC gearmotor with a brake driving a pair of 3" dia. ... The gears have a grove cut deep in the faces. ... The wire rides in the groove, ...
    (rec.crafts.metalworking)