PSN-L Email List Message
Subject: Re: Thermal Control for Sensors
From: ChrisAtUpw@.......
Date: Mon, 19 Nov 2007 09:33:24 EST
In a message dated 19/11/2007, skmort@............ writes:
Hi Chris,
Actually as I understand it, it is the switch off temp that is fixed! In
other words, once the temp has reach its operational point, the control starts
skipping cycles to maintain a max set temp?
Hi Stephen,
That is what I have assumed from your description. Say you set it up in
Summer with an air temperature of 30 C.
The ground temperature minimum may be 20 C, giving a comfortable
temperature difference of 10 C Deg.
You leave it at the same setting in the winter when the ground
temperature has fallen to -5 C
The heater still maintains a top temperature of 30 C, giving a
differential within the case of 35 C deg instead of 10 C Deg. This is likely large
enough to cause convection noise within the case.
If you can supply just enough heat to follow the ground temperature
fluctiations + say 10 Deg, this would be ideal. It would also use less power.
Maybe you could use two thermistors? If you send me the circuit, I will
have a look.
Regards,
Chris Chapman
In a message dated 19/11/2007, skmort@............ writes:
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FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DCourier color=3D#000000 siz=
e=3D3>Hi Chris,
Actually as I understand it, it is the s=
witch=20
off temp that is fixed! In other words, once the temp has reac=
h=20
its operational point, the control starts skipping cycles to maintain a ma=
x=20
set temp?
Hi Stephen,
That is what I have assumed from your descripti=
on.=20
Say you set it up in Summer with an air temperature of 30 C.
The ground temperature minimum may be 20 C, giv=
ing=20
a comfortable temperature difference of 10 C Deg.
You leave it at the same setting in the=20
winter when the ground temperature has fallen to -5 C
The heater still maintains a top temperature of=
30=20
C, giving a differential within the case of 35 C deg instead of 10 C Deg. Th=
is=20
is likely large enough to cause convection noise within the case.
If you can supply just enough heat to follow th=
e=20
ground temperature fluctiations + say 10 Deg, this would be ideal. It would=20=
also=20
use less power.
Maybe you could use two thermistors? If you sen=
d me=20
the circuit, I will have a look.
Regards,
Chris Chapman
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