Author Topic: "internal temp" from bridge?  (Read 2746 times)

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Offline SufferinSuccotash

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"internal temp" from bridge?
« on: April 06, 2015, 09:58:01 PM »
Anyone out there using a hardware/software solution to monitor data from the bridge?  I have looked at the internal temp measured by the bridge and it does not really jive with the temp around the bridge.  Mine reads about 10° F too low! compared to a very accurate thermistor placed beside the bridge.  Anyone else have this discrepancy?

Offline vreihen

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Re: "internal temp" from bridge?
« Reply #1 on: April 07, 2015, 06:39:19 AM »
Mine reads over 90F all the time, but it is located on top of a stack of electronics that generate heat.....
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Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #2 on: April 07, 2015, 12:53:07 PM »
I don't think the operating temperature of the barometric sensor was ever intended to indicate the general room temperature.

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #3 on: April 07, 2015, 02:29:07 PM »
I think you are right... however .. exactly what is this temp and how is it used?

Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #4 on: April 07, 2015, 03:08:33 PM »
I think you are right... however .. exactly what is this temp and how is it used?

It's the operating temperature of the barometric sensor itself.  It's necessary as part of the process for determining the absolute pressure reading from the sensor.  Depending on where it is placed, it may or may not reflect accurate room temperature.

I think Acurite was more concerned that people orient the bridge for best radio reception, not for accurate room temperature, so the temperature function was set aside.

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #5 on: April 07, 2015, 03:25:14 PM »
My thoughts were that it is likely used to calculate the correct pressure but it does not seem to be calibrated.  If anything it measures a temp below ambient!  I therefore wondered if this was the case with other bridges.  Do you see that with your bridge?

Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #6 on: April 07, 2015, 03:40:56 PM »
My thoughts were that it is likely used to calculate the correct pressure but it does not seem to be calibrated.  If anything it measures a temp below ambient!  I therefore wondered if this was the case with other bridges.  Do you see that with your bridge?

I typically ignore that value so I can't really say, but I just took a look and it's reading 4F degrees lower than the wall thermometer in another room.  The bridge is sitting next to a cold window in an unheated room, so I can't that it's a very good comparison.

Offline aweatherguy

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Re: "internal temp" from bridge?
« Reply #7 on: April 08, 2015, 12:24:03 AM »
FWIW, I've been poking around inside my 02032C console, and there's a Measurement Specialties MS5607 barometer module in there. Temperature accuracy for the barometer module is specified at +-2.0C from -20 to 85C. I would not be surprised if the bridge uses the same barometer module...anyone looked inside a bridge?

http://www.meas-spec.com/product/pressure/MS5607-02BA03.aspx

Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #8 on: April 08, 2015, 12:29:56 AM »
FWIW, I've been poking around inside my 02032C console, and there's a Measurement Specialties MS5607 barometer module in there. Temperature accuracy for the barometer module is specified at +-2.0C from -20 to 85C. I would not be surprised if the bridge uses the same barometer module...anyone looked inside a bridge?

http://www.meas-spec.com/product/pressure/MS5607-02BA03.aspx

Yes, people have looked inside the bridge.  It's not the same sensor as what's in the 2032c.

http://www.hoperf.com/upload/sensor/HP03S.pdf
« Last Edit: April 08, 2015, 12:32:54 AM by nincehelser »

Offline DoctorKnow

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Re: "internal temp" from bridge?
« Reply #9 on: April 08, 2015, 08:14:38 PM »
Anyone out there using a hardware/software solution to monitor data from the bridge?  I have looked at the internal temp measured by the bridge and it does not really jive with the temp around the bridge.  Mine reads about 10° F too low! compared to a very accurate thermistor placed beside the bridge.  Anyone else have this discrepancy?

Do you have the bridge near an A/C vent? It appears to be sensitive to rapid changes in temp. Mine runs real close to what I run my air conditioner and heat to. The barometer once calibrated, runs very accurately in my experiences. A meteobridge will show you the bridge air temp.

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #10 on: April 08, 2015, 08:20:20 PM »
Do you have the bridge near an A/C vent? It appears to be sensitive to rapid changes in temp. Mine runs real close to what I run my air conditioner and heat to. The barometer once calibrated, runs very accurately in my experiences. A meteobridge will show you the bridge air temp.


No. it is on its own... and like I said.  I have a very accurate thermistor right beside it to give the "true" temp.  I'm just confused by the reading since it is 10° F below ambient.

Offline DoctorKnow

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Re: "internal temp" from bridge?
« Reply #11 on: April 08, 2015, 08:26:51 PM »
Do you have the bridge near an A/C vent? It appears to be sensitive to rapid changes in temp. Mine runs real close to what I run my air conditioner and heat to. The barometer once calibrated, runs very accurately in my experiences. A meteobridge will show you the bridge air temp.


No. it is on its own... and like I said.  I have a very accurate thermistor right beside it to give the "true" temp.  I'm just confused by the reading since it is 10° F below ambient.

You may have a bad connection on the inside of the bridge to the temp sensor. I have seen where people have had duds right out of the box, meaning the barometer doesn't work, and it could be because of the chip being poorly installed.

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #12 on: April 08, 2015, 08:35:16 PM »

You may have a bad connection on the inside of the bridge to the temp sensor. I have seen where people have had duds right out of the box, meaning the barometer doesn't work, and it could be because of the chip being poorly installed.


Well it seems that the temp is the only thing that is off.  the pressure is in line with other PWS's around me.

Offline DoctorKnow

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Re: "internal temp" from bridge?
« Reply #13 on: April 08, 2015, 08:43:47 PM »
I wouldn't worry then. The temp sensor wasn't meant to be seen anyway I don't think. Also the transmitter inside the bridge is a mystery.

Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #14 on: April 08, 2015, 09:15:14 PM »
You may have a bad connection on the inside of the bridge to the temp sensor. I have seen where people have had duds right out of the box, meaning the barometer doesn't work, and it could be because of the chip being poorly installed.

There is no connection to a temp sensor inside the bridge.  That's because there is no discrete temperature sensor.

The temperature is derived from the 13 values transmitted by the barometric sensor.

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #15 on: April 08, 2015, 09:25:31 PM »

There is no connection to a temp sensor inside the bridge.  That's because there is no discrete temperature sensor.

The temperature is derived from the 13 values transmitted by the barometric sensor.


So the "temp" is a calculated value.  This is derived from the barometric readings?

Offline nincehelser

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Re: "internal temp" from bridge?
« Reply #16 on: April 08, 2015, 09:47:36 PM »

There is no connection to a temp sensor inside the bridge.  That's because there is no discrete temperature sensor.

The temperature is derived from the 13 values transmitted by the barometric sensor.


So the "temp" is a calculated value.  This is derived from the barometric readings?

Well, not in a meteorological sense.

The baro sensor sends out 11 coefficients set at the factory, most having something to do with temperature and other calibration values, then you have a raw signal relating to pressure and temperature.

You have to run all those values that through a set of equations to get the "absolute" or "station" pressure.  This is done outside of the bridge, likely due to it not have much in the way of computational ability.

The code ends up looking something like this:

Code: [Select]
        $c1 = hex ($c1);
        $c2 = hex ($c2);
        $c3 = hex ($c3);
        $c4 = hex ($c4);
        $c5 = hex ($c5);
        $c6 = hex ($c6);
        $c7 = hex ($c7);
        $a  = hex ($a);
        $b  = hex ($b);
        $c  = hex ($c);
        $d  = hex ($d);
        $pr = hex ($pr);
        $tr = hex ($tr);

        $d1 = $pr;
        $d2 = $tr;

        if ($d2 >= $c5)
                {
                $dut = $d2-$c5-(($d2-$c5)/2**7) * (($d2-$c5)/2**7)*$a/2**$c;
                }
                else
                {
                $dut = $d2-$c5-(($d2-$c5)/2**7) * (($d2-$c5)/2**7)*$b/2**$c;
                };

        $off = ($c2 + ($c4 - 1024) * $dut / 2**14) * 4;
        $sens = $c1 + $c3 * $dut / 2**10;
        $x = $sens * ($d1 - 7168) / 2**14 - $off;
        $p = $x * 10 / 2**5 + $c7;

        $t = 250 + $dut*$c6/2**16-$dut/2**$d;

The temperature is the $t value, but you have to divide it by 10 to get a proper Celsius value.

These equations are supplied by the manufacturer of the baro sensor.  Baro sensors from other manufacturers and models will likely be different, so these equations might not work for the consoles.  I know they don't work for the 2032c console, for example.

Note this just gets you "absolute" or "station" pressure.  Further work is needed to reduce it to MSL or Altimeter, or whatever.  I usually just apply a fixed offset based on the local airport reading.
« Last Edit: April 08, 2015, 09:50:33 PM by nincehelser »

Offline SufferinSuccotash

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Re: "internal temp" from bridge?
« Reply #17 on: April 10, 2015, 10:04:28 AM »

Well, not in a meteorological sense.

The baro sensor sends out 11 coefficients set at the factory, most having something to do with temperature and other calibration values, then you have a raw signal relating to pressure and temperature.

You have to run all those values that through a set of equations to get the "absolute" or "station" pressure.  This is done outside of the bridge, likely due to it not have much in the way of computational ability.

The code ends up looking something like this:

Code: [Select]
        $c1 = hex ($c1);
        $c2 = hex ($c2);
        $c3 = hex ($c3);
        $c4 = hex ($c4);
        $c5 = hex ($c5);
        $c6 = hex ($c6);
        $c7 = hex ($c7);
        $a  = hex ($a);
        $b  = hex ($b);
        $c  = hex ($c);
        $d  = hex ($d);
        $pr = hex ($pr);
        $tr = hex ($tr);

        $d1 = $pr;
        $d2 = $tr;

        if ($d2 >= $c5)
                {
                $dut = $d2-$c5-(($d2-$c5)/2**7) * (($d2-$c5)/2**7)*$a/2**$c;
                }
                else
                {
                $dut = $d2-$c5-(($d2-$c5)/2**7) * (($d2-$c5)/2**7)*$b/2**$c;
                };

        $off = ($c2 + ($c4 - 1024) * $dut / 2**14) * 4;
        $sens = $c1 + $c3 * $dut / 2**10;
        $x = $sens * ($d1 - 7168) / 2**14 - $off;
        $p = $x * 10 / 2**5 + $c7;

        $t = 250 + $dut*$c6/2**16-$dut/2**$d;

The temperature is the $t value, but you have to divide it by 10 to get a proper Celsius value.

These equations are supplied by the manufacturer of the baro sensor.  Baro sensors from other manufacturers and models will likely be different, so these equations might not work for the consoles.  I know they don't work for the 2032c console, for example.

Note this just gets you "absolute" or "station" pressure.  Further work is needed to reduce it to MSL or Altimeter, or whatever.  I usually just apply a fixed offset based on the local airport reading.


Thanks for taking the time to explain that.  I guess if there is no actual sensor in the bridge then it must be a generated value. 


It seems to me that the Acurite "system" is rather complicated.  It has to deal with many different setups.  I can envisage different sensors, sending in data through either a console using their software or through a bridge.