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Surely this situation is easy to test for. The temperature increase for
a given heater current will be hugely higher if the heat-sink
(objective) is not in good contact. It shouldn't be difficult to
implement a check for this in the controller circuitry.
Xuejun's other point was sensor failure - and again surely the circuitry
should check for this. Likely failure modes are open circuit or short
circuit - both easily testable conditions, at least if the sensor is a
thermistor or other resistive device.
Guy
Sponsor my next half-marathon on May 15th
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From: Confocal Microscopy List [mailto:[log in to unmask]]
On Behalf Of Dan Focht
Sent: Thursday, 24 March 2011 6:46 AM
To: [log in to unmask]
Subject: Re: Objective Heaters Commercial response
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Xuejun
Thank you for pointing out the overheating issue with Pe-Con.
I did not know theirs would do that!
There is a safety circuit in the Bioptechs objective heater that
continuously looks for the temperature to drop out of a 0.9 degree error
window.
When and if this happens it is due to an improperly attached objective.
When the temperature sensor goes cool beyond the error window, after
having warmed the objective, all power to the heater is shut off and an
annoying alarm goes off on the controller.
This is done to safeguard the objective.
The only time the heater-band overheats is if someone turns the
controller on with the heater plugged in to the controller but NOT
attached to an objective!
The system needs something to heat to complete the control loop.
We cannot help it if somebody does not attach it properly.
Our newest Objective Heater now has a secondary retaining strap to
provide a secure attachment to the objective.
The power cord is detachable so you can have several heaters on the
nosepiece, rotate the nosepiece and just plug in the one you want to use
when you want to use it.
Like I said other companies have copied the idea of warming an objective
but not the technology.
If you have a damaged Objective Heater, call for a RMA number to send it
in for repair.
Dan
On Mar 23, 2011, at 2:28 PM, Xuejun SUN wrote:
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Thanks, Dan, but I like to emphasize this sentence:
"As long as the Objective Heater is attached correctly to the objective,
we
have had no problems."
None of the objective heaters I used (Pecon through Zeiss we got and
Bioptechs) has any safe-guard mechanisms built-in, E.g if the
temperature
sensor fails to read correctly, you might end up with a toasted lens or
heater. In the case of Pecon, one of the few we had, we had an instance
that
temperature runs to the level of so hot that I could not hold it in my
hands
because the wire of the temp. sensor broke inside (which one does not
know
with the simple controller we disposed of). The Bioptech one, if it is
not
attached properly (hard to monitor in a multi-user facility), you will
smell
burning plastic soon.
My advice: get away from objective heater and get an scope enclosure if
you
could afford one.
Regards,
Xuejun
Xuejun SUN, Ph.D.
Faculty Service Officer
Dept. Exp. Oncology
Cross Cancer Institute
11560 University Ave.
Edmonton Alberta, T6G1Z2
Phone (780) 432-8898 (office)
(780) 432-8468/8458 (lab)
Fax: (780) 432-8425
Preferred Email: [log in to unmask]
-----Original Message-----
From: Confocal Microscopy List [mailto:[log in to unmask]]
On
Behalf Of Dan Focht
Sent: Tuesday, March 22, 2011 5:06 PM
To: [log in to unmask]
Subject: Re: Objective Heaters Commercial response
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Neil
There are significant differences in the design and operation of
Objective
Heaters.
I have studied this extensively and used the results of these studies to
develop and produce the Bioptechs Objective heater system.
Our system is not just a copy of an idea it is the first commercial,
patented, Objective Heater System.
Other companies have copied the idea of warming an objective but not the
technology behind it.
Here are a few of the differences between the Bioptechs and other
companies
products.
In my opinion as an engineer, the Bioptechs Objective Heater System
provides
the most efficient, accurate and safe means of objective temperature
control.
. Most efficient - heat is transferred to the barrel of the objective
by
the highest efficiency conductive means by a thin film heater directly
in
contact with the most thermally conductive surfaces of the objective.
Therefore, 97% of the heat developed in the heater goes directly into
the
objective. This statement is backed up with thermographic images from a
military grade quantitative IR camera. Images are on our web site.
This is a significant concern because any heat that does not go into the
objective radiates outward and upward in the direction of the specimen.
As an example, if you touch the heater band of a Bioptechs Objective
heater
you cannot tell the difference from its temperature and the rest of the
objective.
Try that with a Silicone blanket or ring heater and you will feel what I
mean.
In an efficient system, it only requires between 1.3 to 1.7 watts of
energy
to warm an average objective from 22 to 37 degrees C.
Any system that uses more energy than that is not only wasteful but you
have
to consider where this excess energy is going!
In addition, not only do you need to warm the objective, you also have
to
overcome the constant heat-sinking effect of the nosepiece. All the
more
reason for an efficient heat transfer. Another reason that thermal
transfer
efficiency is important is that the control loop runs more efficiently
because thermal corrections can take place on the fly instead of waiting
a
long time for the effect of energy changes to take effect due to thermal
inertia.
. Accuracy - The Bioptechs Objective heater is controlled by a closed
loop
feedback based on the actual temperature of the objective. This is
accomplished by warming the objective about 3/4 of its diameter and
measuring the heat that has been transferred to the objective in an
adjacent
location away from the heat transfer surface. Therefore, the system is
based on the temperature of the objective and not on the temperature of
a
simplistic heater ring!
The temperature of the heated ring is not what is important as long as
it
does not do damage.
What you care about is the temperature at the specimen plane and that
the
objective is not harmed.
Therefore, our operating setpoint is determined at the specimen plane of
the
objective.
Other systems simply regulate the temperature of the heating collar with
no
regard to the temperature at the place that really matters, the specimen
plane!
We do a thermal profile of objectives with the quantitative IR camera to
know how they behave when heated.
. Safety- Bioptechs has been producing objective heaters for 18.5 years
for
all modes of microscopy. We have found that even daily temperature
cycling
has never caused damage to an objective. Our controllers, with their
safety
shutdown and alarm circuitry, warms the objective up over a 15 minute
period
of time so there is no thermal shock to the objective. If you held an
objective in your hand it would warm up faster than that! As long as
the
Objective Heater is attached correctly to the objective, we have had no
problems.
I have seen warm air blowers, velcro attached heaters or blankets, and
heated metal rings all of which have the afore mentioned issues.
I you feel comfortable trusting your objective to a silicone rubber
heater
held in place with velcro or a clamp on metal ring I can't help.
If you want to try one of our systems just call and we will arrange a
free
demo.
Additional information:
http://www.bioptechs.com/Products/OBJ_HTR/obj_htr.html
Movie:
http://www.bioptechs.com/movies/product/ObjectiveHtrdvd06.mov
We have distributors all over the world and would be happy to serve you.
We are very detailed in identifying the correct Objective Heater for
your
objective.
Therefore, we need to know the exact objective you want to control.
Dan
On Mar 22, 2011, at 5:14 PM, Neil Kad wrote:
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I want to use an objective heater for my home-built TIRF. I have an
Olympus
1.45NA objective and more temperature control would be nice.
What kind of objective heaters are used out there and is there anything
I
need to watch out for?
Cheers
Neil
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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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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