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Title: HMP RH and AirT Comparison 12-2017
Date:2017-12-18
Data File: HMPCompare_201712.csv
HMPCompare_201801.csv
Refers to:TA,EE,WP,SW,MB,W07030036,G4540021,U3030041,G45400253,G4540025,L1740420,T2130005,L2310736,U2120013,L2310711,U3030046,T1250012

From 2017-12-18 to 2017-12-19, twelve HMP45s and HMP60s were compared at the Twitchell Alfalfa site. There was one reference (master) sensor. For more details about setup, see field notes from 2017-12-18, 2017-12-19, 2018-01-11, 2018-01-16, and 2018-01-31.

All sensors were set up on the N side of the tower, under the flux sensors. Sensors 4, 5, 6 are on the eddy post. The other 9 sensors are on a separate metal bar.

Location Serial No. Site Model Wiring Data Order Last Cal Fan New T Cal (R2=99%) New RH Cal (R2=99%) Status
1 sn W0730036 Lab HMP45 SE 17, 18 9 2017-05-05 12V 0.1A 0.17m3/min y=0.96808*x+-0.10046 y=0.95446*x+0.12369 Ok
2 sn G4540021 Master HMP60 SE 1, 2 1 2017-04-03 12V 0.04A, 0.11m3/min n/a n/a n/a
3 sn U3030041 Lab HMP45 SE 15, 16 8 2009-12-01 No Fan y=0.95229*x+-0.12176 y=1.0289*x+0.017553 Ok
4 sn G4540023 EE HMP60 SE 9, 10 5 2012-03-12 Unknown y=0.97571*x+0.074027 y=1.0484*x+-0.0082041 Ok
5 sn G4540025 WP HMP60 SE 7, 8 4 2012-03-12 Unknown y=1.0096*x+-0.11377 y=1.0237*x+-0.98393 Ok
6 sn L1740420 TA HMP60 SE 11, 12 6 2015-09-28 24V 0.09A 0.19m3/min y=1.0415*x+-1.0049 y=1.1035*x+-4.9594 Ok
7 sn T2130005 Lab HMP45 SE 21, 22 11 From Siyan 12V 0.1A 0.17m3/min y=1.0131*x+-0.17404 y=1.0657*x+-0.84346 Ok
8 sn L2310736 SW HMP60 SE 5, 6 3 2015-09-28 Unknown y=0.89081*x+2.6501 (R2=97) y=1.0073*x+-0.68692 More testing needed
9 sn U2120013 MB HMP45 SE 13, 14 7 1999-08-18 Unknown y=1.0214*x+-0.085362 y=1.0606*x+-4.5595 Ok
10 sn L2310711 Lab HMP60 SE 3, 4 2 2015-09-28 12V 0.04A, 0.11m3/min y=1.0352*x+-0.048208 y=0.99795*x+-1.56 Ok
11 sn U3030046 Lab HMP45 SE 23, 24 12 2012-04-17 12V 0.1A 0.17m3/min fan y=1.0287*x+-0.28056 y=0.99337*x+2.9056 Ok
12 sn T1250012 Lab HMP45 SE 19, 20 10 From Siyan 12V 0.1A 0.17m3/min fan y=1.0462*x+-0.13614 y=1.0369*x+-0.86214 Ok

Air temperature data generally matched within specifications: +/-0.6C (HMP60) and +/-0.5C (HMP45). The TA sensor was ~1C warmer and the SW sensor was ~2-3C cooler than the other sensors.

Figure 1. Time series of air temperatures.

Relative humidity data generally matched within specifications: +/-5% (HMP60) and +/-3% (HMP45).

Figure 2. Time series of relative humidity

Linear regressions for air temperature and relative humidity between the master and test sensors had tight lines; the only exception was air temperature data from the SW sensor.

Regression Data

Residuals

Figure 3. Linear Regressions for air temperature.

Regression Data

Residuals

Figure 4. Linear Regressions for relative humidity.

From 2018-01-11 to 2018-01-31, two sensors were compared at the Twitchell Alfalfa site. From 2018-01-11 to 2018-01-16, the sensors had no fans and were not aspirated. (Missing data from this period was caused by sporadic power outages at the site.) On 2018-01-16, we added new 24V fans to both sensors to collect aspirated data. Aspirating the sensors made more of a difference for air temperature data than relative humidity data.

When not aspirated, the two sensors did not necessarily match with air temperature specifications: measurement difference was 1.5-2.5 degC. However, when aspirated, the air temperature difference between the two sensors was 0.6-1 degC, meeting the specification of +/- 0.6 degC.

Figure 5. Time series of aspirated vs. non-aspirated air temperature.

Aspiration made less difference for relative humidity measurements. Without aspiration, the two relative humidity measurements were about 5% different; with aspiration, the two measurements were about 4% different. 

Figure 8. Time series of aspirated vs. non-aspirated relative humidity.

There is a slight offset difference between aspirated vs. non-aspirated air temperature. However, the regression lines are right on top of each other for aspirated vs. non-aspirated relative humidity, again showing that aspiration affects air temperature but not relative humidity data.

Regression Data

Residuals

Figure 7. Linear regressions for aspirated vs. non-aspirated air temperature.

Regression Data

Residuals

Figure 6. Linear regressions for aspirated vs. non-aspirated relative humidity.

 

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