LI-COR LI-600, Instruction Manual

Page: 98 / 131

Section 9. Theory of operation
9-11
equations 9-12a and 9-12b). A prerequisite to starting a
calibration is access to tank air or a column of chemical
to scrub H
2
O from the airstream. Ensure dry conditions
prior to resetting a zero, which can take 30 minutes or
more of flowing dry air across the sensors.
Upon initiation, the calibration routine averages 10
seconds of data for
T
ref
and V
x
and then recalculate the
zero intercept:
9-36
After calculating b
xnew
, the user must confirm the new
setpoint. The new value will then stored to memory.
RH sensor span
Resetting the span setpoint is an adjustment of the para-
meter
S
x
in equations 9-13a and 9-13b for each sensor,
respectively. A prerequisite to starting a calibration is
access to a known H
2
O source, such as a dewpoint gen-
erator. The known quantity might be in a dewpoint tem-
perature, or potentially in mole fraction units. The
software will accept either unit and convert to the cor-
rect relative humidity at the sensor using equations 9-7,
9-21, and 9-25, with
Press coming from the LI-600 pres-
sure sensor and T
ref
coming from the LI-600 reference
thermistor.
The span setting requires all calibration parameters for a
given sensor from equations 9-12a, 9-12b, 9-13a, 9-13b,
9-14a, and 9-14b, as well as
rh
true
, current reference tem-
perature T
ref
and the voltage of the sensor V
x
.
Upon initiation, the calibration routine averages 10
seconds of data for
T
ref
and V
x
and then re-calculate the
span