Subject:
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Re: Sensor Reliability
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 7 Feb 2000 16:31:20 GMT
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Viewed:
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1667 times
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In lugnet.robotics, Ben Jackson writes:
> In lugnet.robotics, Dave Baum writes:
> [regarding the accuracy of the LEGO temperature sensor]
> > Not very accurate - perhaps within 2 or 3 degrees F. The display uses 0.1
> > degrees precision (either C or F), but the accuracy just isn't there.
>
> My recent experience with the rotation sensor led me to two conclusions: the
> RAW values measured by the RCX are significantly affected by both battery
> voltage and the length of the connecting wire.
>
> I suspect that the *precision* (repeatability) of the inputs is very high as
> long as you control both of those variables. If you need accurate absolute
> temperature readings you'll need to calibrate with any extension wires you • plan
> to use and use the RCX on an A/C power supply. It's possible (even likely)
> that the default calibration assumes a temperature sensor with no extension
> wires (since it has one built in) and a wall power supply.
>
> BTW, was the incubator monitor that Steve Moffat was talking about ever built?
The reading is affected by wire length, because this introduces more
capacitance in the equation. When the RCX switches off power, and takes a
reading from the sensor, there is only a tiny period of time for the signal to
stabilise at it's new value, and once the wire grows in length, this no longer
happens. The RCX does stabilise the power delivered during the 'sense' phase
on the active sensors, but the delivered power during the 'power' phase is not
stabilised. However Lego do stabilise the power inside their sensors, but it
is a question of 'level'. They use a simple one transistor current source, to
stabilise the delivered power into their LED drive circuit, and this is quite
stable really, but is affected by temperature, and only gives a 'real'
accuracy of a few percent.
Fun Huh...
Best Wishes
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Message is in Reply To:
 | | Re: Sensor Reliability
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| In lugnet.robotics, Dave Baum writes: [regarding the accuracy of the LEGO temperature sensor] (...) My recent experience with the rotation sensor led me to two conclusions: the RAW values measured by the RCX are significantly affected by both (...) (25 years ago, 7-Feb-00, to lugnet.robotics)
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