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:
<= 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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