Hello,
I would ask you what is the best position for probes and sensor. I have dew removal for a ED80 and a 60mm guide telescope and they get very hot at 100% of power so I was wondering what the best position is in order to be sure all OTA is warm enough to avoid dew. Also temp/hum sensor shoul be placed where dew does not wet it at all, what's your solution/suggestions?
Thanks in advance,
Regards.
Giovanni
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For refractors, The dew strap should be placed over the front cell assembly (ie the glass front cell).
You do not want to heat all the OTA, only the front cell as that is where dew will form. Heating the entire OTA will cause excessive thermal currents in the tube which will impact on image quality.
The temp sensor for the heat strap should be located as close as possible to the dew strap, BUT NOT underneath the dew strap. I tape mine on just below the dew strap with clear tape. Lay it flat so it makes contact.
For the Ambient Temp/Humidity sensor, its normally mounted on the outside of the dew controller so it is exposed to the air. The dew controller is preferably strapped to a tripod leg or the mount pier. (Not on the ground as that will affect the temp/humidity sensor with false readings).
Why are you running it at 100%? Looking at the dew controller app you should see the OTA temp either at ambient or above ambient temperature by 1 or 2 degrees at most, depending on which temperature tracking mode is selected.
Last edit: brownrb 2016-10-10
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Hello
Thanks for the suggestion. Meanwhile I noticed my home made dew removal nichel cromo makes a weak sound when it's on: is it normal ??? May it affects ccd read noise??
Best regards
Giovanni
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Hi Giovanni
Maybe. Its possible the nickel wire is acting as an antenna and if the correct length could then emit signals which could be picked up by the CCD both as read noise or disturbance in the image. I assume that the noise is at the pitch frequency of the PWM you are using to control the strap, if its audible then it might not be, a lot depends on the closeness of the ccd and dew starp, the amount of power, the switching frequency, the amount of RFI shielding in the camera etc.
Probably unlikely,
As bias frames are so short, they would hardly be affected. It is more likely to tutn up in darks, so I would take a 2m dark with the dew controller on, then another with the dew controller off and use a program that can measure the noise levels to see if there is any difference. If they are around the same then it should not be an issue.
Cheers
Robert
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Hello,
I think I solved the issue. I changed frequency of Arduono pwn dew channel pins from 480Hz to 31Khz and the noise has disapperead. Duty Cycle does not change and dew removals work well. I also tried to get dark and bias frames with and without dew removal on and it seems there's no interference.
Thanks for your support.
Clear skies,
Giovanni.
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Hello Giovanni,
could you please help: I can't find wehre to change the frequency. I built my own heating stripes and they sounds. And why did you decide to set the frequency to 31Khz?
Kind regards
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hello,
I would ask you what is the best position for probes and sensor. I have dew removal for a ED80 and a 60mm guide telescope and they get very hot at 100% of power so I was wondering what the best position is in order to be sure all OTA is warm enough to avoid dew. Also temp/hum sensor shoul be placed where dew does not wet it at all, what's your solution/suggestions?
Thanks in advance,
Regards.
Giovanni
Hi Giovanni
For refractors, The dew strap should be placed over the front cell assembly (ie the glass front cell).
You do not want to heat all the OTA, only the front cell as that is where dew will form. Heating the entire OTA will cause excessive thermal currents in the tube which will impact on image quality.
The temp sensor for the heat strap should be located as close as possible to the dew strap, BUT NOT underneath the dew strap. I tape mine on just below the dew strap with clear tape. Lay it flat so it makes contact.
For the Ambient Temp/Humidity sensor, its normally mounted on the outside of the dew controller so it is exposed to the air. The dew controller is preferably strapped to a tripod leg or the mount pier. (Not on the ground as that will affect the temp/humidity sensor with false readings).
Why are you running it at 100%? Looking at the dew controller app you should see the OTA temp either at ambient or above ambient temperature by 1 or 2 degrees at most, depending on which temperature tracking mode is selected.
Last edit: brownrb 2016-10-10
Hello
Thanks for the suggestion. Meanwhile I noticed my home made dew removal nichel cromo makes a weak sound when it's on: is it normal ??? May it affects ccd read noise??
Best regards
Giovanni
Hi Giovanni
Maybe. Its possible the nickel wire is acting as an antenna and if the correct length could then emit signals which could be picked up by the CCD both as read noise or disturbance in the image. I assume that the noise is at the pitch frequency of the PWM you are using to control the strap, if its audible then it might not be, a lot depends on the closeness of the ccd and dew starp, the amount of power, the switching frequency, the amount of RFI shielding in the camera etc.
Probably unlikely,
As bias frames are so short, they would hardly be affected. It is more likely to tutn up in darks, so I would take a 2m dark with the dew controller on, then another with the dew controller off and use a program that can measure the noise levels to see if there is any difference. If they are around the same then it should not be an issue.
Cheers
Robert
Hello,
I think I solved the issue. I changed frequency of Arduono pwn dew channel pins from 480Hz to 31Khz and the noise has disapperead. Duty Cycle does not change and dew removals work well. I also tried to get dark and bias frames with and without dew removal on and it seems there's no interference.
Thanks for your support.
Clear skies,
Giovanni.
Hi Giovanni
Glad to hear you solved the problem,
Happy imaging!
Robert
Hello Giovanni,
could you please help: I can't find wehre to change the frequency. I built my own heating stripes and they sounds. And why did you decide to set the frequency to 31Khz?
Kind regards