Temp sensing, finally

iceman (Mike) · #1 02-05-2006, 03:02 PM

Ok i've finally made some steps to start active cooling..

First things first though.. measuring the temperature.

Went to d.ick smith and got a digitor Slimline Electronic Dual Thermometer for $30, and also some thermal paste for $4.

So, what now?

I take it the "indoor" temperature is measured from on the unit itself - therefore this should be my "amient" temperature measurement? Where should I put this on my scope? Anywhere on the base with velcro?

The "outdoor" temperature is measured by a sensor at the end of a 3m long wire. I take it this is my "mirror" temperature measurement? So do I glue this sensor onto the side of my mirror, with the thermal paste?

What else do I need to know?

Thanks in advance.

RB (Andrew) · #2 02-05-2006, 03:17 PM

Quote:

Originally Posted by iceman

The "outdoor" temperature is measured by a sensor at the end of a 3m long wire. I take it this is my "mirror" temperature measurement? So do I glue this sensor onto the side of my mirror, with the thermal paste?

What else do I need to know?

Thanks in advance.

The thermal paste acts as a medium for the heat transfer, it will not hold the sensor in place. You need to secure the sensor somehow.

matt · #3 02-05-2006, 03:18 PM

That sounds about right, Mike.

I'm not sure exactly where you place the mirror sensor and how you insulate it for accuracy? DP I'm sure will have the good oil on this bit.

But the only other thing is to maybe buy a couple of cable tidy's

Welcome to SpaghettiVille

davidpretorius · #4 02-05-2006, 03:18 PM

good boy,

yes indoor measures the ambient and the one on the lead should fit up that little hole on the mirror cell. I have mine half way up the side of the mirror.

i would put some velcro on the outside of your tube, so that whilst imaging, you easily look over and check temps at any time.

no glue, just the paste should hold it in place

davidpretorius · #5 02-05-2006, 03:26 PM

as long as you do not pull on the lead, i have found the sensor stays in place with the thermal paste.

i used to have a polystyrene strip that went over the top to make sure the sensor was measuring the mirror as much as possible, but found the plastic surrounds of the sensor do that job very well

matt · #6 02-05-2006, 03:30 PM

So just leave the sensor "as is" and attach it to the side of the mirror with the thermal paste? That's it?

RB (Andrew) · #7 02-05-2006, 03:33 PM

Quote:

Originally Posted by davidpretorius

as long as you do not pull on the lead, i have found the sensor stays in place with the thermal paste.

Cool (pardon the pun)

I was thinking more along the lines of permanency.

davidpretorius · #8 02-05-2006, 03:45 PM

i have found it to be strong enough not to fall off with normal alt/az movement etc, and no doubt you will want to clean your mirror once a year, so it is handy if it can come off.

make sure it is not too close to the top of the mirror and dont swamp the paste on.

matt · #9 02-05-2006, 05:04 PM

OK. Back from my own little shopping trip where I bought the same indoor/outdoor temp sensor and thermal paste.

DP - In regards to attaching the outdoor sensor to the mirror with the paste. Is it just a case of applying a small dob to the side of the mirror and pressing the sensor into that dob, or do you need to also cover the sensor with paste?

The other thing is: when to take the temp readings? Is it OK to watch the temps while the fan is operating? Won't that give some kind of false reading with the "fanned" air blowing over the outdoor sensor?

That's why I asked about covering the sensor with paste to act as some kind of insulation or shield? Or do you wait to take readings after the fan is switched off?

Thanks in advance

davidpretorius · #10 02-05-2006, 05:18 PM

Quote:

Originally Posted by matt

DP - In regards to attaching the outdoor sensor to the mirror with the paste. Is it just a case of applying a small dob to the side of the mirror and pressing the sensor into that dob, or do you need to also cover the sensor with paste?

The other thing is: when to take the temp readings? Is it OK to watch the temps while the fan is operating? Won't that give some kind of false reading with the "fanned" air blowing over the outdoor sensor?

there was some double sided tape on my sensor which i pulled off and then had a look at the sensor itself. it is contained within a plastic shell. by putting a dab of paste on the mirror and pushing the sensor into it, i believe that this is enough. you can insulate it further, but I am yet to be convinced.

the fan will be blowing ambient air over the sensor true, but i do not notice any rise in apparent mirror temp as the fans are swtiched off. and i am blowing aprox 5 degree below ambient air over the mirror.

Starkler (Geoff) · #11 02-05-2006, 07:23 PM

Quote:

Originally Posted by davidpretorius

i would put some velcro on the outside of your tube, so that whilst imaging, you easily look over and check temps at any time.

I wonder if a supercooling steel tube will affect the measurement?

I would also think that the display unit may need a dew shield of its own to prevent supercooling from affecting the reading.

P.S. supercooling is an object becomming colder than ambient due to black body radiation.

iceman (Mike) · #12 02-05-2006, 07:27 PM

Maybe i'll mount it in a cardbox box with a flip-top lid? Keep the dew off and keep it at roughly ambient.

davidpretorius · #13 02-05-2006, 07:34 PM

there might be something in that geoff, i have two sensors, one black one like mikes connected to mirror and its ambient sensors, right next to it on the tube is a white one with one end measuring the cold plate and ambient.

now both ambients are not always the same for the black and white ones even though they are right next to each other on the grey steel tube.

the excess leads are rolled up and sits between the two sensors and the tube

??

matt · #14 03-05-2006, 06:05 AM

Well. Good news. After getting the indoor/outdoor sensor home last night I thought I'd check its accuracy before installing in/on the scope.

When left in a room without any drafts or widely variable temp differences the indoor and outdoor readings came to the same point very quickly.

Quite an accurate little unit.

But like DP recommends, immediately remove the scotch tape covering the outdoor sensor. It affects the sensor's sensitivity.

iceman (Mike) · #15 03-05-2006, 06:13 AM

I tested mine as well.. 22.5° inside the house, took it out and attached it to the scope at 10pm (just on the tube, for the "ambient" reading), and within 5 minutes it was stable at 11.2°.

Will pull the mirror out tonight (if I get time), clean it (well overdue), and secure the "outdoor" sensor to the mirror.

However while playing around last night, I wondered about sticking the unit on the tube.. The tube was very cold to touch.. it felt colder than the actual ambient temperature. I know the sensor on the unit is on top, so it's not in direct contact with the tube, but I wondered if it might still give a false reading.

I wonder if on the base, away from the cold tube, might be a better place for the ambient sensor?

matt · #16 03-05-2006, 06:35 AM

Yeah. Been thinking about the false reading issue myself, Mike.

Maybe someone knows of a good insulating material that we could stick between the tube and the temp unit???

I'd like mine up high where I can see it. I also like your idea of housing it inside some kind of box, to shield it from dew...and drafts etc etc

iceman (Mike) · #17 03-05-2006, 06:48 AM

Yeh, as long as the box doesn't give a false reading itself, as it might be protecting it from the "real" ambient temperature.

matt · #18 03-05-2006, 06:56 AM

Nah. The box should be OK as far as accurate readings go.

Think if all those weather stations where the thermometer's housed in a wooden box with all the other instruments.

davidpretorius · #19 03-05-2006, 08:38 AM

it is ugly, but a little block of polystyrene with velcro either side.

matt · #20 03-05-2006, 04:16 PM

DP. Does that thermal paste "set" or does it remain in the same gooey-soft state?