4 field calibration – Campbell Scientific 247-L Conductivity and Temperature User Manual
Page 10
247 CONDUCTIVITY AND TEMPERATURE PROBES
6
6.4 FIELD CALIBRATION
The cell constant is a dimensional number
expressed in units of cm
-1
. The unit cm
-1
is
slightly easier to understand when expressed as
cm·cm
-2
. Because it is dimensional, the cell
constant as determined at any one standard,
will change only if the physical dimensions
inside the 247 probe change. Error due to
thermal expansion and contraction is negligible.
Corrosion and abrasion, however, have the
potential of causing significant errors.
A field calibration of the 247 cell constant can
be accomplished as follows:
1.
Make a 0.01 molal KCL solution by
dissolving 0.7456 g of reagent grade KCl in
1000 g of distilled water.
2.
Clean the probe thoroughly with the black
nylon brush shipped with the 247 and a
small amount of soapy water. Rinse
thoroughly with distilled water, dry
thoroughly, and place in the KCl solution.
3.
Connect the 247 to the datalogger using the
wiring described in Section 4. Enter the
following program into the datalogger.
The calibration solution temperature must be
between 1°C and 35°C; the polynomial in step 11
(58) corrects for temperature errors within this
range. The solution constant of 1.408 mS cm
-1
,
entered in step 13 (37), is valid only for a 0.01
molal KCl solution. Location 8, generated by step
14, will contain the resultant cell constant.
01:
P5
AC Half Bridge
01:
1
Rep
02:
15
2500 mV fast Range
(5000 mV fast for 21X)
03:
2
IN Chan
04:
1
Excite all reps w/EXchan 1
05: 2500
mV Excitation
(5000 mV for 21X)
06:
1
Loc [:Rs ]
07:
1
Mult
08:
0
Offset
02:
P59
BR Transform Rf[X/(1-X)]
01:
1
Rep
02:
1
Loc [:Rs ]
03:
1
Multiplier (Rf)
03:
P30
Z=F
01:
nnn
F Enter Lead Length
in Feet
02:
00
Exponent of 10
03:
5
Loc [:Rp ]
04:
P37
Z=X*F
01:
5
Loc Rp
02:
.00032 F
03:
5
Loc [:Rp ]
05:
P37
Z=X*F
01:
5
Loc Rp
02:
-.1
F
03:
5
Loc [:Rp ]
06:
P34
Z=X+F
01:
5
Loc [Rp ]
02:
-.005
03:
5
Loc [:Rp ]
07:
P33
Z=X+Y
01:
1
X Loc Rs
02:
5
Y Loc Rp
03:
1
Z Loc [:Rs ]
08:
P11
Temp 107 Probe
01:
1
Rep
02:
3
IN Chan
03:
2
Excite all reps w/EXchan 2
04:
2
Loc [:t]
05:
1
Mult
06:
0
Offset
09:
P34
Z=X+F
01:
2
X Loc t
02:
-25
F
03:
3
Z Loc [:(t-25).01]
10:
P37
Z=X*F
01:
3
X Loc (t-25).01
02:
.01
F
03:
3
Z Loc [:(t-25).01]
11:
P55
Polynomial
01:
1
Rep
02:
3
X Loc (t-25).01
03:
4
F(X) Loc [:f(t) ]
04:
.99124 C0
05:
-1.8817
C1
06:
3.4789
C2
07:
-3.51
C3
08:
-1.2
C4
09:
-43
C5
12:
P42
Z=1/X
01:
4
X Loc f(t)
02:
6
Z Loc [:1/f(t) ]
13:
P37
Z=X*F
01:
6
X Loc 1/f(t)
02:
1.408
F
03:
7
Z Loc [:Act'l Con]
14:
P36
Z=X*Y
01:
7
X Loc Act'l Con
02:
1
Y Loc Rs
03:
8
Z Loc [:Kc (cm-1)]