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 kΩ) and the cable
length (0.000032 kΩ 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 ]
To Next Page
Loading...
Need help?
General
