![background image](http://html1.mh-extra.com/html/campbell/kh20/kh20_user-manual_3876052020.webp)
KH20 Krypton Hygrometer
A-2
4
4.5
5
5.5
6
6.5
7
7.5
8
1.74
3.02
4.17
5.44
6.71
7.95
9.2
10.47 11.69
12.9
14.22 15.46 16.78 18.04 19.25
KH
2O
Ou
tp
u
t (m
V
)
Vapour Density (g/m
3
)
Figure A-1. KH20 ln(mV) vs. Vapour Density
We can perform the linear regression on the plot above to obtain the slope for the
relationship between the ln(mV) and the vapour density. The slope for the graph
above will be the coefficient,
k
w
x
which we are after. Table A-1 below shows the
result of linear regression analysis. Again the slope is the product of the
absorption coefficient of water vapour,
k
w
, and the KH20 path length,
x
.
Table A-1. Linear Regression Results for KH20 ln(mV)
vs. Vapour Density
Description
Values
Slope (xk
w
) -0.205
Y Intercept (ln(V
0
) 8.033
If we substitute these values, along with the measured lnV into equation A-3, we
can obtain the water vapour density,
ρ
w
. Campbell Scientific, Inc. performs the
calibration twice for each KH20: once with the window cleaned, and again with
the window scaled. We then break up the vapour density range into dry and wet
ranges, and compute the
k
w
values for each sub range, as well as for the full range.
If you know the vapour density range for your site, it is recommended that you
select the coefficient,
k
w
, that is appropriate for your site, the dry range or the wet
range. If the vapour range for the site is unknown, or if the vapour range is on the
border line between the dry and the wet ranges, use the value for the full range.
Table A-2 shows the final calibration values the KH20 calibration certificate
contains. The data shown in Table A-2 is from an actual KH20.