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Sensirion sht1 reads high — Parallax Forums

Sensirion sht1 reads high

Ray0665Ray0665 Posts: 231
edited 2011-03-04 13:40 in Accessories
I have the sensirion sht1 on the Prop demo board and am using the Sensirion.spin object from the obex.
It is consistently returning a high reading of almost 3 degrees C (5F). I' have it compensated for VCC of 3.3 volts and modified it to return a fixed point value scaled by 1000 as follows
' celsius = 1000(-39.63 + (0.01t))
return 10*ReadTemperature-39630

does anyone have any suggestion?

Comments

  • Tracy AllenTracy Allen Posts: 6,664
    edited 2011-03-04 08:15
    Hi Ray,

    I have to ask, what is the reference sensor and is it in direct contact with the SHT on the demo board?

    The SHT11 would not have that much self heating, less than 0.1 deg. Celsius when reading twice per second.
  • Ray0665Ray0665 Posts: 231
    edited 2011-03-04 10:40
    By reference sensor I assume you want to know how I know it is off?
    The bottom line is I don't, but I have a Galileo thermometer in the same room and a Lacross 2300 base station in the same room and both read lower than the sensiron, and they are physically close enough to the sensor that it should be in the same range. I don't expect a match but I think 5F is a bit much.
    To be clear there are two objects in the exchange, I am not using Sensirion_full so I don't have access to the heaters with this object.
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2011-03-04 11:52
    I'd be inclined to trust the Sensirion and look for other reasons it might be at a 3 °C higher temperature. There can be substantial variation in a room from place to place. The Sensirion is in its own micro-environment mounted on the white block on the demo board, and the voltage regulators or even a nearby lamp may be generating heat. The best comparison would be something like a DS1620 mounted side by side on the block. I don't see anything wrong with your math.

    The LaCross weather station is in its own micro-environment too. I don't know about its accuracy, but I wouldn't be at all surprised if it also uses the Sensirion sensor too. The SHT series is very popular.
    The Galileo (buoyancy) thermometer, I don't know, how accurate can those be?
  • Ray0665Ray0665 Posts: 231
    edited 2011-03-04 12:09
    Well I do have a DS1620 I think I'll put it on the board too just to see.
    Tracy , before I forget thanks for responding...

    After my reply I moved the Galileo right next to the demo board and there are no lights on in the room.
    I honestly don't know about the Galileo but the tags are marked at 2F increments.

    May I assume, from the lack of other suggestions that other than environment it is what it is with regards to the SHT1?
  • Ray0665Ray0665 Posts: 231
    edited 2011-03-04 13:40
    Well Well Well I now have the DS1620 and the Sht1 right next to each other on the demo board
    and I am seeing readings within 1 degree F of each other, well within expected tolerances.

    I guess I'm now like the proverbial guy with three watches
    Anyway thanks again.
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