From sam at wa4phy.net Wed Dec 1 20:28:14 2004 From: sam at wa4phy.net (Sam Drinkard) Date: Wed Dec 1 20:28:18 2004 Subject: [wxqc] Barometer drift? Message-ID: I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman From dshelms at comcast.net Thu Dec 2 00:05:07 2004 From: dshelms at comcast.net (Sandy and David Helms) Date: Thu Dec 2 00:05:15 2004 Subject: [wxqc] Barometer drift? Message-ID: Hi Sam, Elevation differences account for 00.001 INS per 1 foot elevation difference or 00.025 inch of mercury in your case (re: 25 ft elevation difference). With a 2 mb difference (or 00.06 INS), this accounts for about 1/3 of the noted difference. However if you are comparing altimeter readings, the elevation differences are already built into the solutions as altimeter is pressure reduced to sea level. If your area is seeing anything more than light winds, you should assume that the pressure gradient will contribute to an additional difference in pressures between the stations. When doing pressure comparisons, its best to wait for a calm day. The other issue to is to make sure the valid times of the comparisons are within a few minutes of each other. Since most ASOS METAR reports are available at hourly intervals, on the hour (but aren't posted to the Internet until 10 minutes past the hour), I usually call the ASOS/AWOS computer voice automated phone number and get a simultaneous altimeter reading. Here's the info for the stations in your area: AGS Reports from WX ASOS: PHONE 706-790-0631 http://www.airnav.com/airport/KAGS DNL Reports from WX ASOS: PHONE 706-481-8629 http://www.airnav.com/airport/KDNL I don't think the 70-75F degree variance is significant contributor to your pressure variance. If possible, you should try to keep the pressure instrument away from a direct influence of a HVAC vent which might cause small spikes in pressure. You may ask Santa for a second stand-alone barometer to act as a local pressure value. The goal is to be within 00.03 INS of a local standard. Hope this helps, Dave CW0351 -----Original Message----- From: wxqc-bounces@lists.gladstonefamily.net [mailto:wxqc-bounces@lists.gladstonefamily.net]On Behalf Of Sam Drinkard Sent: Wednesday, December 01, 2004 8:28 PM To: wxqc@lists.gladstonefamily.net Subject: [wxqc] Barometer drift? I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman _______________________________________________ wxqc mailing list wxqc@lists.gladstonefamily.net http://pond1.gladstonefamily.net:8080/mailman/listinfo/wxqc From sam at wa4phy.net Wed Dec 1 20:28:14 2004 From: sam at wa4phy.net (Sam Drinkard) Date: Wed, 1 Dec 2004 20:28:14 -0500 Subject: [wxqc] Barometer drift? Message-ID: I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman From dshelms at comcast.net Thu Dec 2 00:05:07 2004 From: dshelms at comcast.net (Sandy and David Helms) Date: Thu, 2 Dec 2004 00:05:07 -0500 Subject: [wxqc] Barometer drift? Message-ID: Hi Sam, Elevation differences account for 00.001 INS per 1 foot elevation difference or 00.025 inch of mercury in your case (re: 25 ft elevation difference). With a 2 mb difference (or 00.06 INS), this accounts for about 1/3 of the noted difference. However if you are comparing altimeter readings, the elevation differences are already built into the solutions as altimeter is pressure reduced to sea level. If your area is seeing anything more than light winds, you should assume that the pressure gradient will contribute to an additional difference in pressures between the stations. When doing pressure comparisons, its best to wait for a calm day. The other issue to is to make sure the valid times of the comparisons are within a few minutes of each other. Since most ASOS METAR reports are available at hourly intervals, on the hour (but aren't posted to the Internet until 10 minutes past the hour), I usually call the ASOS/AWOS computer voice automated phone number and get a simultaneous altimeter reading. Here's the info for the stations in your area: AGS Reports from WX ASOS: PHONE 706-790-0631 http://www.airnav.com/airport/KAGS DNL Reports from WX ASOS: PHONE 706-481-8629 http://www.airnav.com/airport/KDNL I don't think the 70-75F degree variance is significant contributor to your pressure variance. If possible, you should try to keep the pressure instrument away from a direct influence of a HVAC vent which might cause small spikes in pressure. You may ask Santa for a second stand-alone barometer to act as a local pressure value. The goal is to be within 00.03 INS of a local standard. Hope this helps, Dave CW0351 -----Original Message----- From: wxqc-bounces at lists.gladstonefamily.net [mailto:wxqc-bounces at lists.gladstonefamily.net]On Behalf Of Sam Drinkard Sent: Wednesday, December 01, 2004 8:28 PM To: wxqc at lists.gladstonefamily.net Subject: [wxqc] Barometer drift? I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman _______________________________________________ wxqc mailing list wxqc at lists.gladstonefamily.net http://pond1.gladstonefamily.net:8080/mailman/listinfo/wxqc From sam at wa4phy.net Wed Dec 1 20:28:14 2004 From: sam at wa4phy.net (Sam Drinkard) Date: Wed, 1 Dec 2004 20:28:14 -0500 Subject: [wxqc] Barometer drift? Message-ID: I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman From dshelms at comcast.net Thu Dec 2 00:05:07 2004 From: dshelms at comcast.net (Sandy and David Helms) Date: Thu, 2 Dec 2004 00:05:07 -0500 Subject: [wxqc] Barometer drift? Message-ID: Hi Sam, Elevation differences account for 00.001 INS per 1 foot elevation difference or 00.025 inch of mercury in your case (re: 25 ft elevation difference). With a 2 mb difference (or 00.06 INS), this accounts for about 1/3 of the noted difference. However if you are comparing altimeter readings, the elevation differences are already built into the solutions as altimeter is pressure reduced to sea level. If your area is seeing anything more than light winds, you should assume that the pressure gradient will contribute to an additional difference in pressures between the stations. When doing pressure comparisons, its best to wait for a calm day. The other issue to is to make sure the valid times of the comparisons are within a few minutes of each other. Since most ASOS METAR reports are available at hourly intervals, on the hour (but aren't posted to the Internet until 10 minutes past the hour), I usually call the ASOS/AWOS computer voice automated phone number and get a simultaneous altimeter reading. Here's the info for the stations in your area: AGS Reports from WX ASOS: PHONE 706-790-0631 http://www.airnav.com/airport/KAGS DNL Reports from WX ASOS: PHONE 706-481-8629 http://www.airnav.com/airport/KDNL I don't think the 70-75F degree variance is significant contributor to your pressure variance. If possible, you should try to keep the pressure instrument away from a direct influence of a HVAC vent which might cause small spikes in pressure. You may ask Santa for a second stand-alone barometer to act as a local pressure value. The goal is to be within 00.03 INS of a local standard. Hope this helps, Dave CW0351 -----Original Message----- From: wxqc-bounces at lists.gladstonefamily.net [mailto:wxqc-bounces at lists.gladstonefamily.net]On Behalf Of Sam Drinkard Sent: Wednesday, December 01, 2004 8:28 PM To: wxqc at lists.gladstonefamily.net Subject: [wxqc] Barometer drift? I've come almost to the conclusion that the Davis barometers have somewhat of a temperature drift associated with them, altho at this point, I have no solid data to back up that statement. I do plan to run some experiments to either prove or disprove. Reason, I've been following rather closely, the readings and difference or lack thereof, between my station reading and both KAGS and KDNL. DNL is about 6nm from me, and elevations are within 25' or so, yet I seem to be seeing as much as 2mb or more difference between us, yet yesterday, during my periodic tracking of the two, we were exactly together for quite a number of hours. Is there any logical explaination for this or could there really be that much difference in pressure in only 6nm ? At other times, AGS, which is roughly 14.3nm from here and I track relatively close, with DNL being somewhat of an outlier as compared to surrounding stations. Altho I try to maintain a constant temperature here in the computer room where the console of the WM-II is located, at times, the temp will exceed what I like to keep it at (approx 75?F), but never drops below about 70?. Any comments from others? --- Snowman _______________________________________________ wxqc mailing list wxqc at lists.gladstonefamily.net http://pond1.gladstonefamily.net:8080/mailman/listinfo/wxqc