Campbell Scientific 247-L Conductivity and Temperature User Manual
Page 8
247 CONDUCTIVITY AND TEMPERATURE PROBES
4
11:
P6
Full Bridge
01:
1
Rep
02:
14
250 mV fast Range
(Use 500 mV fast for 21X)
03:
1
IN Chan
04:
1
Excite all reps w/EXchan 1
05: 2500
mV Excitation
(Use 5000 mV for 21X)
06:
1
Loc [:Rs ]
07:
-.001
Mult
08:
1
Offset
12:
P95
End
13:
P95
End
14:
P59
BR Transform Rf[X/(1-X)]
01:
1
Rep
02:
1
Loc [:Rs ]
03:
1
Multiplier (Rf)
Subtract resistance errors (Rp) caused by the
blocking capacitors (0.005 k
Ω) and the cable
length (0.000032 k
Ω ft
-1
). Enter cable lead
length in nnn below.
15:
P30
Z=F
01:
nnn
F Enter Lead Length
in Feet
02:
00
Exponent of 10
03:
5
Loc [:Rp ]
16:
P37
Z=X*F
01:
5
Loc Rp
02:
.00032 F
03:
5
Loc [:Rp ]
17:
P37
Z=X*F
01:
5
Loc Rp
02:
-.1
F
03:
5
Loc [:Rp ]
18:
P34
Z=X+F
01:
5
Loc [Rp ]
02:
-.005
03:
5
Loc [:Rp ]
19:
P33
Z=X+Y
01:
1
X Loc Rs
02:
5
Y Loc Rp
03:
1
Z Loc [:Rs ]
EC is then calculated by multiplying the
reciprocal of resistance, which is conductance,
by the cell constant to arrive at EC.
NOTE: The cell constant (K
c
) is printed on the
label of each sensor. It is entered in place of
nnn in this segment.
20:
P42
Z=1/X
01:
1
X Loc Rs
02:
2
Z Loc [:1/Rs ]
21:
P37
Z=X*F
01:
2
X Loc 1/Rs
02:
nnn
F ENTER CELL
CONSTANT
03:
3
Z Loc [:Ct ]
Temperature Temperature is measured with a
single instruction, P11, that measures the
thermistor resistance and calculates
temperature. Output is °C when a multiplier of
1 and an offset of 0 is used. See Section 10 for
detailed information on the function of
Instruction P11.
22:
P11
Temp 107 Probe
01:
1
Rep
02:
3
IN Chan
03:
2
Excite all reps w/EXchan 2
04:
4
Loc [:Temp °C ]
05:
1
Mult
06:
0
Offset
5.3 CORRECTION OF IONIZATION ERRORS IN
EC MEASUREMENT
Ionization caused by the excitation of the EC
sensor can cause large errors. Campbell
Scientific has developed a linear correction for
measurements between 0.005 and 0.44 mS cm
-1
,
and a quadratic correction for measurements
between 0.44 and 7.0 mS cm
-1
. Corrections were
determined in standard salt solutions containing
KCl, Na
2
SO
4
, NaHCO
3
, and NaCl.
The following program segment automatically
chooses which correction to apply to the
measurement.
23:
P89
If X<=>F
01:
3
X Loc Ct
02:
4
<
03:
.474
F
04:
30
Then Do
24:
P37
Z=X*F
01:
3
X Loc Ct
02:
.95031 F
03:
3
Z Loc [:Ct ]