right place this time
maybe a silly question but where is the best place to put the temp sensors on a newt
i am using 2 heaters one on the guide scope and one on the bottom of the main ota
should I be measuring the temp close to the heater tape?
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Hi
I do not have any experience with Newts but the principle is the same for each type of scope.
When you idenify the optics (or lens etc) that you want dew NOT to form on -
the heating strap should be placed as near to the optics as possible - this might be on the back of the mirror block - the heating strap should never be placed inches away - it must be as close as possible
The reasons for this are - we have better control over temperature because we are not trying to heat up other things - there is more efficient heat transfer so we can keep the power down, we are not heating the tube itself and creating heat waves in the tube - which is a bad thing
We use a temp probe because - we need to measure the optics temperature. If we just used a sensor to read ambient humidity and dew point then that is not good enough. At nigh time with a dark clear sky, and the telescopes pointing upwards, the dark sky acts as a heat sponge to optics - though the ambient temp might be say 0, the actual temp of optics can be -3 or -4 because the dark sky acts as a huge heat sink for optics and literally sucks the heat from the optics - meaning the optics cool down and thus reach a temp below ambient temp as of course as they cool down - well dew forms.
So then comes the question where does the temperature probe go?
We cannot place it under the heat strap because then we are really measuring the heat strap and not the convected heat to the optics.
With a large mirror area we have good choices - but with a front lens cell of a refractor or eyepiece we do not have many choices.
I tend to lay the metal end of the probe flat on the surface about 1/2 to 1" away from the strap. I then can compensate for the reading using channel offsets or when I am using multiple dew straps, I tend to adjust the tracking offset by about 1 degree C to compensate for the fact the the temp probe is reading the convected heat and thus is a little below the actual heat.
Hope that helps
Robert
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
right place this time
maybe a silly question but where is the best place to put the temp sensors on a newt
i am using 2 heaters one on the guide scope and one on the bottom of the main ota
should I be measuring the temp close to the heater tape?
Hi
I do not have any experience with Newts but the principle is the same for each type of scope.
When you idenify the optics (or lens etc) that you want dew NOT to form on -
the heating strap should be placed as near to the optics as possible - this might be on the back of the mirror block - the heating strap should never be placed inches away - it must be as close as possible
The reasons for this are - we have better control over temperature because we are not trying to heat up other things - there is more efficient heat transfer so we can keep the power down, we are not heating the tube itself and creating heat waves in the tube - which is a bad thing
We use a temp probe because - we need to measure the optics temperature. If we just used a sensor to read ambient humidity and dew point then that is not good enough. At nigh time with a dark clear sky, and the telescopes pointing upwards, the dark sky acts as a heat sponge to optics - though the ambient temp might be say 0, the actual temp of optics can be -3 or -4 because the dark sky acts as a huge heat sink for optics and literally sucks the heat from the optics - meaning the optics cool down and thus reach a temp below ambient temp as of course as they cool down - well dew forms.
So then comes the question where does the temperature probe go?
We cannot place it under the heat strap because then we are really measuring the heat strap and not the convected heat to the optics.
With a large mirror area we have good choices - but with a front lens cell of a refractor or eyepiece we do not have many choices.
I tend to lay the metal end of the probe flat on the surface about 1/2 to 1" away from the strap. I then can compensate for the reading using channel offsets or when I am using multiple dew straps, I tend to adjust the tracking offset by about 1 degree C to compensate for the fact the the temp probe is reading the convected heat and thus is a little below the actual heat.
Hope that helps
Robert
perfect thanks
have a great Christmas