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Guy
The Bioptechs series 5 Objective Heater System was not designed to detect the presence of an objective because we did not think anybody would run it without being attached to an objective.
However, it has happened although not often. In our next series of Bioptechs Objective heaters we will include that feature.
We are always responsible to our customers request and that is a good one.
When I get back from AACR I will begin implementing this feature.
Note, that the instructions indicate that the operator should never run the objective heater without a load and should observe the digital display to confirm proper expected operation.
One reason the controller does not detect the presence of an objective is that the temperature sensor is always at rom temp at the beginning of the heating process.
Therefore, room temp is expected and not out of the ordinary. Also given the differences to thermal profiles of different objectives and different potential sources of heat that could influence the sensor we cant always look for a heat rise to occur. What I will do is to place a pressure sensor on the heater "cube", BTW the machinist already thinks it is Swiss Cheese given all the holes in it, to not allow the activation of the heating circuit until the heater cube is secured firmly against the objective. That should do it!
I have never suggested or advised that an objective should be heated as high as 50 degree C. I was just illustrating the acceptable range as allowed by manufacturers.
I know it was Stephen Cody that mentioned Warner, Thank you Stephen!
Dan
> Maybe I should point out to Dan that it was Steve Cody, not Wamer, who
> mentioned their product. Both Steve and I are interested in the whole
> range of these products simply because we cater for a wide range of
> users, we teach courses for all comers, and (in my case at least) write
> books for the whole gamut of life-science researchers.
>
>
>
> So I would still be interested to get a response from Dan to my query -
> why is it that his controller cannot detect that the heater is detached
> from the lens? It should be simple.
>
>
>
> As to the temperature a lens can handle, I am sure 50C is not a problem
> but it is vital to heat it slowly - there is a lot of glass there and it
> is a very poor conductor of heat. (Brass isn't that good but it's a lot
> better than glass). I suspect a body at 50C with optics at 20C would be
> disastrous.
On Mar 28, 2011, at 4:24 PM, Dan Focht wrote:
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Stephan
I agree that boxing the whole microscope or stage and objective area is a solution.
However, for those who don't want to box the scope for a variety of reasons. The following applies.
From the Warner web page:
"Heat generated by the isolated collar is not directly communicated to the objective but is instead distributed around the objective via a conducting sleeve."
When I read this my first impression is, "What?, they intentionally isolate the heat source from the objective!"
That means they rely on radiation, which goes in all directions (not just toward the objective) and a little conductivity from air, another inefficient heat transfer means.
Thermal conductivity of air 0.024 W/(m.oC). Thermal conductivity of brass 109 W/(m.oC). In terms of thermal transfer efficiency, there is no comparison, not even in the ball park!
Again from the Warner site:
"The conducting sleeve warms the surrounding air, which in turn gently warms the objective. This approach allows the apparatus to take full advantage of the thermal characteristics of the surrounding air. The warmer achieves its task without directly contacting or exposing the objective to significant stresses associated with temperature gradients."
I look at it this way.
I know the thermal characteristics of air, and it is poor.
You have an objective screwed into a nosepiece that you want to warm to 37 degrees C.
The objective is about 150 to 225 grams of brass, glass and airspace not to mention the mass of the nosepiece.
I mention the mass of the nosepiece because it acts as a heat sink requiring constant compensation thus more energy to maintain constant temperature.
1. Do you think you can accurately transfer enough heat to warm the objective with the additional thermal drain of the nosepiece from an air-spaced heat source without excessive heat being produced in the vicinity of the objective where it radiates outward and upward?
2. Do you think you can maintain a constant accurate temperature when you have to wait for the heat to be transferred through air to get to the objective without inducing excessive temperature cycling?
It is the inefficiency of heat transfer that causes cycling. We thermally profile objectives to be certain that the surface that heat is transferred from or to is as efficient as possible to minimize
3. If your thermal transfer efficiency is as good as it should be, the heat source only has to be only a couple of percent higher than the temperature of the objective.
Given the thermal inefficiency of air, I never even entertained using air to conduct heat to an objective.
However, if someone out there has one of these and would lend it to me for a couple of days, I would be glad to do a thermal propagation time-lapse of it with our military grade quantitative IR camera.
It would be in movie form and I would make it available to anyone that wants it. This is a costly thing to do but the data would be worth it.
Note, All four major microscope manufacturers have issued a letter to me that the objectives can withstand up to 50 degrees C. I thought that was generous but understandable.
The temperature of the objective can get a lot higher than 37 degrees while it is sitting in the delivery truck waiting to be delivered.
Note, I refrained from naming other companies in my first reply. Now that the door is open, I guess ,SWAG, I can walk in.
Dan
> From: Stephen Cody <[log in to unmask]>
> Date: March 27, 2011 10:30:22 PM EDT
> To: [log in to unmask]
> Subject: Re: Objective Heaters
> Reply-To: Confocal Microscopy List <[log in to unmask]>
>
> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> Dear List,
>
> For the sake of completeness I think the Warner objective heater should be
> mentioned. This differs slightly from those discussed so far, in that the
> heating collar is not directly coupled to the lens. There is instead a
> deliberate air space between the heating collar and lens. Presumably this
> adds a little capacitance to the heat transfer process. It may reduce some
> of the tendency for temperature cycling. It also is their way of simplifying
> the build to suit different shapes and sizes of lens, although they sell
> small, medium and large versions. It should avoid problems with badly
> attached heat sensors. Presumably the heat sensor is on the collar itself or
> in the airspace, this would result in a slow, but conservative heating
> mechanism.
>
> I myself use heated chambers that enclose the stage and objectives, with a
> sub-incubator to control CO2 / Oxygen / Nitrogen and humidity.
>
> See link: http://www.warneronline.com/product_info.cfm?id=1365&name=Objective
> Warmers
>
>
> Caveats: I haven't used any commercial objective heaters,
> No commercial affiliation with any objective heater companies.
>
> --
> Stephen H. Cody
Dan Focht
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Bioptechs, Inc.
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Dan Focht
Bioptechs, Inc.
3560 Beck Rd.
Butler, PA 16002
www.bioptechs.com
P: (724)282-7145
F: (724)282-0745
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