How to insulate a digital thermometer IC?

I want to design a digital thermometer with Dallas's DS1631 to measure current outdoors temperature, just outside a window or so.
I need some ideas on how to insulate the IC and still get the correct outside temperature.
My ideas are:
*Fixing the IC against the window
*Fixing the IC on the aluminium casing of the window
*Insulate the IC somehow and put it outside.
I don't know which one should be the most correct one to pick up the current actual temperature outside.
The last idea seems to be the best as the others might pick up only the window or the alluminium temperature, but I don't know how to insultate the IC and still pass the current temperature correctly.

If anyone has any ideas i'd appreciate it very much.

Tkx

Re: Digital Thermometer

Usually you want to measure the air temperature, so don't attach it to anything like a window, etc. Use an insulated mount and thin wires (they will conduct heat from inside the house which will give you a small error). Cover it so the sun can't shine directly on it and so it doesn't get wet in the rain but allow plenty of air circulation. Route wires to droop down at the sensor so water can't run down the wires into the sensor.

Re: Digital Thermometer

Microemission said:

My ideas are:
*Fixing the IC against the window

Click to expand...

Will have some errors. The moisture will kill it if it's not insulated

*Fixing the IC on the aluminium casing of the window

Click to expand...

Will have large thermal inertia and will not measure the real outside temperature

*Insulate the IC somehow and put it outside.

Click to expand...

The best option. One ideea is to use a thin glass (0.5mm maximum thin) and the IC imersed in oil. As small oil quantity (a recipient which IC dimension will fit inside) as small thermal inertia. Silicone vaseline instead oil as well.

If anyone has any ideas i'd appreciate it very much.

Tkx

Click to expand...

Re: Digital Thermometer

Tkx guys, you've been very helpfull.

melc said:

The best option. One ideea is to use a thin glass (0.5mm maximum thin) and the IC imersed in oil. As small oil quantity (a recipient which IC dimension will fit inside) as small thermal inertia. Silicone vaseline instead oil as well.

Click to expand...

Kitchen oil will do?
The biggest problem is to find a small glass case to put the IC in.

One more thing, is it better the IC package to be SMD type or DIP type for this purpose? I have both thats why I'm asking

Re: Digital Thermometer

Microemission said:

Tkx guys, you've been very helpfull.

melc said:

The best option. One ideea is to use a thin glass (0.5mm maximum thin) and the IC imersed in oil. As small oil quantity (a recipient which IC dimension will fit inside) as small thermal inertia. Silicone vaseline instead oil as well.

Click to expand...

Kitchen oil will do?

Kitchen oil is not very good because in time will smell ugly (and looks ugly) because of oxidation

Click to expand...

The biggest problem is to find a small glass case to put the IC in.

There are some 3-4mm diameter glass tubes for chemical purposes. If you'll melt one end in a fire (a real fire with oxigen) become what you need

Click to expand...

One more thing, is it better the IC package to be SMD type or DIP type for this purpose? I have both thats why I'm asking

Click to expand...

SMD is better because is smaller and the whole assembly will have lower inertia

Click to expand...

Re: Digital Thermometer

An interesting experiment would be to make 2 sensors and put one in oil and one next to it in air. Then bring all the wires inside to a switch so you could switch back and forth to see what the difference is.
If you do this, please report the results back to us!

Re: Digital Thermometer

@melc
Besides Silicone vaseline that you refered what kind of oil would be appropriate then?

There are some 3-4mm diameter glass tubes for chemical purposes. If you'll melt one end in a fire (a real fire with oxigen) become what you need

Click to expand...

Yes I do remember playing with those on chemistry classes
I know what to look for now!!

newelltech said:

An interesting experiment would be to make 2 sensors and put one in oil and one next to it in air. Then bring all the wires inside to a switch so you could switch back and forth to see what the difference is.
If you do this, please report the results back to us!

Click to expand...

Can be totally done, as the IC's run on I2C bus, and have selectable addresses, so no need for switch.
Still need to code it in a AVR, but I forsee no problems, I will report the results when I finish building it.

Re: Digital Thermometer

newelltech said:

An interesting experiment would be to make 2 sensors and put one in oil and one next to it in air. Then bring all the wires inside to a switch so you could switch back and forth to see what the difference is.
If you do this, please report the results back to us!

Click to expand...

A more simple experiment will be the temperature measurement using two identical sensors, both of them mounted EXACTLY in the same conditions in a closed box (avoiding air flow) first very close one to each other and second at 50cm distance.

The next experiment is to multiply with 5 or more sensors, spreaded in your room (from the floor to the ceiling) and see the result. You'll be surprised, believe me !


The best temperature sensor I've used was the DS18B20 in BGA package (1.6x2mm).

Re: Digital Thermometer

Why would you want to mount 2 sensors in the same enclosed box?
The goal is to measure the air temperature. The most accurate way to do this is to mount the sensor in the air but restricting wind effects as much as possible. The suggestion to put the sensor in a small, thin walled container filled with oil is to prevent moisture from affecting the readings. Even a small amout of moisture on the sensor will reduce the reading due to evaporation effects. The oil filled approach keeps water off the sensor, although the container itself will experience evaporative effects but to a lesser extent. The oil mass also helps conduct away any self-heating that the sensor may have, which would also affect the reading.

When you put a temperature sensor in an enclosed box, it will produce erroneous readings and will be very slow to react to temperature changes. The enclosure will insulate the sensor from the outside air which is the opposite of what you want. It will also collect and keep heat that the sensor produces (even a little heat will build up). It's like putting a temperature sensor in a thermos bottle.

I'm not sure of the value of measuring the air temp at various heights in the room. Everyone knows that heat rises so the top will be warmer. How much warmer will depend on the circulation of the air and whether the heater or air conditioner is running.