The biggest problem we encountered is not mentioned. The heat drain
of the (oil emersion) lens is so big that it will ruin all your
efforts to get the heat from your stage to the cells. Best thing in
my opinion is to heat your lens (and your stage).
 
Gert van Cappellen
 
> Jim Pawley wrote:
>
> >We made quite an effective air-curtain system out of a regular $20 hair
> >dryer and a 110 vac, 300 watt temperature controller (from Omega? About
> >$230.  You won't need the 700-1200 watts of the normal dryer to warm your
> >stage so you put the two heating coils in series and this makes the
> >controller cheaper.).
> >
> >As the motors in most dryers are DC, we made a small variable power supply
> >(about 0-15 volt as I remember but you can measure it. ) for it to get the
> >flow that we wanted and hooked the controller to the heating element and to
> >a temperature sensor (think we used a copper/constantan thermocouple)
> >buried into the metal of the stage (to dampen short term temperature
> >variations).  The only problem was that the warm wind tended to dry out any
> >preparation that wasn't very water tight.
>
> We have done more or less the same thing, but there seems to be more to the
> design of these things than meets the eye. I would like to hear anyone's
> opinions (especially yours, Jim) on some of these issues:
>
> 1. If you place the temperature sensor in the stage, the system will
> probably take a long time to come to equilibrium due to the thermal mass of
> the stage. Overshoot may be a problem. Also, at startup, your heater will
> be running open loop (i.e., as much power as it can put out) due to the
> thermal lag of the stage. If you have not limited the max power output of
> the heater, this could result in very hot air being blown at the specimen.
> The only solution I had here was to limit the power output of the heater
> such that when running at full power, the air temperature was limited to
> about 40-42 degrees C. Of course, this also limits how fast the system can
> come to equilibrium. The basic problem is the limitation with which air can
> transfer heat to these relatively large metal masses.
>
> 2. Another solution to the above problem is to place the temperature sensor
> directly in the air stream, such that the unit is effectively regulating
> the air stream to the desired temperature. If you have done like Jim and
> made the air flow rate adjustable, this should make the system stay in
> regulation better. The problems here are (a) you don't actually monitor the
> stage temperature, so you don't know what it is without an external probe,
> and (b) you are always fighting to overcome the thermal losses of the
> stage, so unless you are really moving a lot of air, the stage will always
> be cooler than the airstream. In our experience of monitoring the cell bath
> with an external fast response time probe, it looks like the airstream
> needs to be two to five degrees hotter than the desired temperature of the
> stage (at about 37 degrees). Most critical of all, of course, is that this
> you are not regulating the temperature of the stage - if you move the air
> curtain, the whole thing will shift its equilibrium point.
>
> 3. Considering the slow thermal response time of such systems, it is
> crucial to have an indication of the instantaneous power being applied to
> your heater so you can tell whether the system is regulating or not. If you
> just look at the temperature and see that it is about where you want it,
> you don't know if that is because the system is regulating, or if it is
> just because the heater is running at full tilt and the system just happens
> to have stabilized there. This could be important if you change samples -
> if the system is not regulating, it make take a very long time for the new
> sample to come up to temperature.
>
>
> ________________________________________________________________________
> Kurt M. Scudder, Research Scientist          tel: +45 4442 1412
> Novo Nordisk BioImage Satellite              fax: +45 4442 1411
> Moerkhoej Bygade 28                          email: [log in to unmask]
> DK-2860 Soeborg, Denmark
>
 
 ========================================================================
Gert van Cappellen, [log in to unmask] Erasmus University,
Endocr.& Reprod., Dr. Molewaterplein 50, 3015 GE Rotterdam, The Netherlands
Fax: +31 10 4366832