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- Logisys multifunction panel (with remote)
April 4, 2008, 1:07 am
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drive bay panel with the two analog meters on the front and the
wireless remote PC power on.
The meters are way off. I'd like to try and tweak them down to
display the actual temps, but the trim pots on the board don't appear
to help very much.
Anyone have any luck tweaking the temp readout with this drive bay
Re: Logisys multifunction panel (with remote)
You should ask the manufacturer, for a calibration procedure.
For example, there are two channels, and two potentiometers per
channel. One could be for "gain" and the other for "offset".
You have to be very careful, when screwing around with stuff like
that, because you may never get the pots adjusted back to the
Another thing to keep in mind with 10 turn or 20 turn pots, is on
some of them, the slider comes off the end of the rail when you
crank them too far. Sometimes it is hard to get them to go back
again. They're not the most robust adjustment devices.
A calibration procedure would consist of using a couple fixed
resistors. The resistors would need to have tight tolerances
(like +/- 1% or better). You would alternate between the
two or more fixed resistors, connecting them to the header,
and making adjustments. The manufacturer probably did something
like that, at the factory.
I cannot tell from the pictures, whether the sensors provided are
thermistor based or transistor based. The circuit they're connected
to, on the Logisys board, appears to be pretty simple. Just a couple
transistors by the looks of it.
Thermistors at least, are not linear devices. This is a resistance table
for a RadioShack thermistor you used to be able to get. RadioShack
no longer sells this one.
RS part# 271-110A
10k +/- 1% @ 25 deg C.
Temperature degrees C versus resistance in K ohms
-50c = 329.2k +35c = 6.941k
-45c = 247.5k +40c = 5.862k
-40c = 188.4k +45c = 4.912k
-35c = 144.0k +50c = 4.161k
-30c = 111.3k +55c = 3.567k
-25c = 86.39k +60c = 3.021k
-20c = 67.74k +65c = 2.589k
-15c = 53.39k +70c = 2.229k
-10c = 42.25k +75c = 1.924k
-5c = 33.89k +80c = 1.669k
0c = 27.28k +85c = 1.451k
+ 5c = 22.05k +90c = 1.366k
+10c = 17.96k +95c = 1.108k
+15c = 14.68k +100c = .9735k
+20c = 12.09k +105c = .8575k
+25 c= 10.0k +110c = .7579k
+30c = 8.313k
A thermistor generally has a nice round number at, say, 25C, and the
resistance then varies above and below that, as the temperature varies.
You'll notice, if you plot those values, that the response of the
thermistor is not linear. On the motherboard hardware monitor, they
use a table lookup, to do the conversion from voltage to temperature,
and that can be used to take care of the non-linearity.
The thermistor has two parameters. A unitless "beta", like 3435, and
the nominal resistance at 25C, which for the above device is 10000 ohms
or 10K ohms. The curvature of the response is what is specified by the
beta. It could be that the two pots, are a way of tweaking for the
temp at 25C and the curvature (beta).
The calibration procedure, would probably not calibrate with an actual
sensor. By using fixed resistors, they could test to see if the meter
reads correctly. For example, they could take a 10000 ohm 1% accurate
resistor, and connect it to the header. The meter should read 25C. Then,
they could connect a 3000 ohm resistor, and check that the meter reads
60C. That would be the basic idea of a calibration procedure. It would be
a nuisance to maintain a water bath at a fixed temp, dip the sensor in
the water (using a test tube to prevent the water from shorting the
sensor), and check the readout that way. The fixed resistor doesn't
take the sensor inaccuracy into account, but does bring the metering
circuit into the ballpark. When you buy the sensor, from a sensor
manufacturer, they can already be screened to 1% accuracy.
I don't know exactly how the circuit on the Logisys board works.
I see a couple transistors, but don't recognize what they might
be doing. The analog meters on the front panel, are current
sensing devices, so a measured voltage from the sensor, is
converted to a current, and that is what the analog meter