| Posted: Friday Oct 12th, 2007 07:42 pm |
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TheMax74
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| Joined: | Monday Jul 16th, 2007 |
| Location: | Italy |
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Hello, i've a question:
where i live, there is no way to use smartfit for hvac control, so i've found a temperature sensor LM35DZ.
This is a transistor, giving a linear response from 0 to 150°C, 10mV / degree. For example, 22°c is 220mV (0,22V)
I wish to use input zone #1 to read the analog voltage, by shunting the pins to double EOL resistors (away of zone input terminals).
Confort analog zone input, reports 0 for 0 Volt, 255 for 3 V.
The problem is that the zone#1 outputs 3.0 V and the temp sensor 0,22V.
3.0V - 0.22V = 2.78V
Using math: 255:3=x:2.78
x=(255*2.78) / 3 = 236
It means that for 2.78V, comfort reports 236. Ok.
My problem is that when temperature changes, there is no change in the value, even if i burn the sensor with fire.
I wired the output of the temp sensor directly to the zone #1, the ground of temp sensor with zone common and the +12V of the sensor with one of +12V of the main board.
Where is the problem?
Thank you!
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| Posted: Saturday Oct 13th, 2007 09:11 am |
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2nd Post |
admin
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| Joined: | Saturday Mar 3rd, 2007 |
| Location: | Singapore |
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The LM35 Supply pin should be connected to 12V and the output of the IC should be connected to the Zone Input (on Comfort or Slave but not the LEM)
The LM35 gives an output proportional to the Celsius scale at 10 mV / deg C
Hence at 40 degrees C you will only get 0.4V, the change will be too small to be useful
You need to amplify the output of the LM35 using an electronic amplifier circuit in order to get a more useful dynamic range say by 6 times which means 60 deg C would give 3.0 V
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| Posted: Saturday Oct 13th, 2007 10:41 am |
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3rd Post |
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