Campbell 247 User manual

INSTRUCTION MANUAL
247 Conductivity and
Temperature Probes
Revision: 3/96
Copyright (c) 1994-1996
Campbell Scientific, Inc.

Warranty and Assistance
The 247-L CONDUCTIVITY & TEMPERATURE PROBE is warranted by
CAMPBELL SCIENTIFIC, INC. to be free from defects in materials and
workmanship under normal use and service for twelve (12) months from date of
shipment unless specified otherwise. Batteries have no warranty. CAMPBELL
SCIENTIFIC, INC.'s obligation under this warranty is limited to repairing or
replacing (at CAMPBELL SCIENTIFIC, INC.'s option) defective products.
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defective products to CAMPBELL SCIENTIFIC, INC. CAMPBELL
SCIENTIFIC, INC. will return such products by surface carrier prepaid. This
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which have been subjected to modification, misuse, neglect, accidents of
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expressed or implied, including warranties of merchantability or fitness for a
particular purpose. CAMPBELL SCIENTIFIC, INC. is not liable for special,
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i
247 Table of Contents
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1. Overview......................................................................1
1.1 EC Sensor .................................................................................................1
1.2 Temperature Sensor..................................................................................1
2. Specifications .............................................................1
2.1 Probe.........................................................................................................1
2.2 EC Sensor .................................................................................................2
2.3 Temperature Sensor..................................................................................2
3. Installation...................................................................2
3.1 Site Selection ............................................................................................2
3.2 Mounting...................................................................................................2
4. Wiring ..........................................................................2
5. Programming ..............................................................2
5.1 Programming Overview............................................................................2
5.2 Measurement Programming......................................................................3
5.3 Correction of Ionization Errors in EC Measurement ................................4
5.4 Correction of Temperature Errors.............................................................5
5.5 Output Processing.....................................................................................5
6. Calibration...................................................................5
6.1 Conversion Factors ...................................................................................5
6.2 Typical Ranges .........................................................................................5
6.3 Factory Calibration ...................................................................................5
6.4 Field Calibration.......................................................................................6
7. Maintenance................................................................7
8. Analysis of Errors.......................................................7
8.1 EC Measurement Error .............................................................................7
8.2 Temperature Measurement Error..............................................................8
9. Deriving a Temperature Compensation
Coeffecient.......................................................................9

10. Instruction 11 Details................................................9
11. Electrically Noisy Environments............................10
12. Long Lead Lengths Temperature...........................10

1
247 CONDUCTIVITY AND TEMPERATURE PROBES
1. OVERVIEW
247 Probes (247-L and 247W-L) are designed for
measuring the electrical conductivity, dissolved
solids, and temperature of fresh water with
Campbell Scientific dataloggers. They require the
use of negative excitation, so they can be used
with the CR10(X), 21X, and CR7 dataloggers but
not with the BDR301 or BDR320.
Electrical conductivity (EC) of a solution is a
simple physical property, but measurements can
be difficult to interpret. This manual instructs the
user how to make EC measurements with the
247. Accuracy specifications apply to
measurements of EC in water containing KCl,
Na2SO4, NaHCO3, and/or NaCl, which are typical
calibration compounds, and to EC not yet
compensated for temperature effects.
Statements made on methods of temperature
compensation or estimating dissolved solids are
included to introduce common ways of refining and
interpreting data, but are not definitive.
Authoritative sources to consult include the USGS
Water-Supply Paper 1473, The pH and Conductivity
Handbook published by OMEGA Engineering,
physical chemistry texts, and other sources.
1.1 EC SENSOR
The EC sensor consists of three stainless steel
rings mounted in an epoxy tube as shown in
Figure 4-1. Resistance of water passing
through the tube is measured by excitation of
the center electrode with positive and negative
voltage. The two outer electrodes return the
signal to the datalogger.
This electrode configuration eliminates the
ground looping problems associated with
sensors in electrical contact with earth ground.
1.2 TEMPERATURE SENSOR
Temperature is measured with a thermistor in a
three wire half bridge configuration.
2. SPECIFICATIONS
2.1 PROBE
Construction: The probe housing is epoxy with
rounded ends to facilitate installation and removal.
Size: Length 3.125". Diameter 0.75". The
diameter of the weighted 247W-L version with
the stainless steel sleeve is 1.05".
Maximum Cable Length: 1000 ft. The sensor
must be ordered with desired length as cable
cannot be added to existing probes.
Depth Rating: Maximum 1000 ft. In
applications that require probe placement in
well casings, the weighted 247W-L is strongly
recommended.
pH Range: Solution pH of less than 3.0 or greater
than 9.0 may damage the epoxy housing.
LAC-2 2292 SOLDER
SIDE
FIGURE 1-1. 247 Conductivity and Temperature Probe

247 CONDUCTIVITY AND TEMPERATURE PROBES
2
2.2 EC SENSOR
Electrodes: Passivated 316 SS with DC
isolation capacitors.
Cell constant: Individually calibrated. The cell
constant (Kc) is found on a label near the
termination of the cable.
Temp. Range of Use: Above freezing to 50°C.
EC Range: Approx. 0.005 to 7.5 mS cm-1.
Accuracy: in KCl and Na2SO4, NaHCO3, and
NaCl standards at 25°C:
±5% of reading 0.44 to 7.0 mS cm-1.
±10% of reading 0.005 to 0.44 mS cm-1.
2.3 TEMPERATURE SENSOR
Thermistor: Betatherm 100K6A1.
Range: 0°C to 50°C.
Accuracy: Error ±0.4°C (See Section 8.2).
3. INSTALLATION
CAUTION: Rapid heating and cooling of the
probe, such as leaving it in the sun and then
submersing it in a cold stream, may cause
irreparable damage.
3.1 SITE SELECTION
The EC sensor measures the EC of water
inside the epoxy tube, so detection of rapid
changes in EC requires that the probe be
flushed continuously. This is easy to
accommodate in a flowing stream by simply
orienting the sensor parallel to the direction of
flow. In stilling wells and ground wells,
however, diffusion rate of ions limits the
response time.
3.2 MOUNTING
The epoxy housing and sensor cable are made
of water impervious, durable materials. Care
should be taken, however, to mount the probe
where contact with abrasives and moving
objects will be avoided. Weighting to facilitate
installation in wells is provided by the stainless
steel sleeve on the 247W-L. Strain on cables
can be minimized by using a split mesh strain
relief sleeve on the cable, which is
recommended for cables over 100 ft. The
strain relief sleeve is available from Campbell
Scientific as part number 7421.
4. WIRING
The 247s manufactured after January 1, 1994
are connected to a Campbell Scientific
datalogger as illustrated in Figure 4-1.
NOTE: The excitation channel used for EC
must be separate from the one used for
temperature or measurement errors will result.
To make previous versions of the 247 (those
without an orange lead) compatible with the
information in this manual, connect existing
wires as shown in Figure 4-1. Attach one end
of a short piece of insulated wire to the
excitation channel servicing the black lead and
the other end to the H side of the selected
differential channel (this wire acts as the absent
orange lead). If your probe has a blue lead, it is
no longer needed. Tape the exposed portion to
avoid shorting the sensor.
5. PROGRAMMING
5.1 PROGRAMMING OVERVIEW
Typical datalogger programs to measure the
247 consist of four parts:
1. Measurement of EC and temperature
2. Correction of ionization errors in EC
measurements
3. Correction of temperature errors in EC
measurements
4. Output processing
All example programs may require modification
by the user to fit the specific application's wiring
and programming needs. Example programs in
this manual assume that the orange lead is
connected to 1H, the white to 1L, the red to 2H,
the green to E2, and the black to E1.

247 CONDUCTIVITY AND TEMPERATURE PROBES
3
FIGURE 4-1. 247 Wiring Diagram
5.2 MEASUREMENT PROGRAMMING.
EC Results from Instructions 5 or 6 (chosen
automatically as part of the autoranging feature
of the following program segment) are
processed with Instruction 59 to produce the
resistance across the electrodes:
Make a preliminary measurement of resistance
for autoranging.
01: P6 Full Bridge
01: 1 Rep
02: 15 2500 mV fast Range
(Use 5000 mV fast for 21X)
03: 1 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation
(5000 mV for 21X)
06: 1 Loc [:Rs ]
07: -.001 Mult
08: 1 Offset
02: P59 BR Transform Rf[X/(1-X)]
01: 1 Rep
02: 1 Loc [:Rs ]
03: 1 Multiplier (Rf)
Test the preliminary measurement against each
case and make a refined measurement.
03: P93 Case
01: 1 Case Loc Rs
04: P 83 If Case Location < F
01: 1.8 F
02: 30 Then Do
05: P5 AC Half Bridge
01: 1 Rep
02: 15 2500 mV fast Range
(Use 5000 mV fast for 21X)
03: 2 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation
(Use 5000 mV for 21X)
06: 1 Loc [:Rs ]
07: 1 Mult
08: 0 Offset
06: P95 End
07: P83 If Case Location < F
01: 9.25 F
02: 30 Then Do
08: P6 Full Bridge
01: 1 Rep
02: 15 2500 mV fast Range
(Use 5000 mV fast for 21X)
03: 1 IN Chan
04: 1 Excite all reps w/EXchan 1
05: 2500 mV Excitation
(5000 mV for 21X)
06: 1 Loc [:Rs ]
07: -.001 Mult
08: 1 Offset
09: P95 End
10: P83 If Case Location < F
01: 280 F
02: 30 Then Do

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 kΩft-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 (Kc) 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, Na2SO4, NaHCO3, 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 ]

247 CONDUCTIVITY AND TEMPERATURE PROBES
5
25: P34 Z=X+F
01: 3 X Loc Ct
02: -.00378 F
03: 3 Z Loc [:Ct ]
26: P94 Else
27: P55 Polynomial
01: 1 Rep
02: 3 X Loc Ct
03: 3 F(X) Loc [:Ct ]
04: -.02889 C0
05: .98614 C1
06: .02846 C2
07: 0.0000 C3
08: 0.0000 C4
09: 0.0000 C5
28: P95 End
5.4 CORRECTION OF TEMPERATURE ERRORS
The effect of temperature on the sample
solution can cause large errors in the EC
measurement. A simple method of correcting
for this effect is to assume a linear relationship
between temperature and EC. This method
generally produces values to within 2% to 3% of
a measurement made at 25°C.
The best corrections are made when the
temperature coefficient is determined at a
temperature near field conditions. See Section
9 for details on how to determine the
temperature coefficient. If determining the
temperature coefficient is not possible, use a
value of 2% °C-1 as a rough estimate.
The following program segment implements a
previously determined temperature coefficient
(TC) and calculates the corrected conductivity.
29: P34 Z=X+F
01: 4 X Loc Temp °C
02: -25 F
03: 6 Z Loc [:A ]
30: P37 Z=X*F
01: 3 X Loc Ct
02: 100 F
03: 8 Z Loc [:100*Ct ]
31: P37 Z=X*F
01: 6 X Loc A
02: nnn F Enter TC (%°C-1)
03: 9 Z Loc [:TC PROCES]
32: P34 Z=X+F
01: 9 X Loc TC PROCES
02: 100 F
03: 9 Z Loc [:TC PROCES]
33: P38 Z=X/F
01: 8 X Loc 100*Ct
02: 9 Y Loc TC PROCES
03: 10 Z Loc [:C25mScm-1]
5.5 OUTPUT PROCESSING
Over large ranges, EC is not linear and is best
reported as samples (70). In limited ranges,
averaging (71) measurements over time may be
acceptable. Convention requires that the
temperature at the time of the measurement be
reported.
6. CALIBRATION
6.1 CONVERSION FACTORS
1 S (Siemens) = 1 mho = 1/ohm
Although mS·cm-1 and µS·cm-1 are the
commonly used units of EC, the SI base unit is
S·m-1. The result of the example programs is
mS·cm-1
EC measurements can be used to estimate
dissolved solids. For high accuracy, calibration
to the specific stream is required. However, for
rough estimates, values between 550 and 750
mg·l-1 / mS·cm-1 are typical with the higher
values generally being associated with waters
high in sulfate concentration (USGS Water-
Supply Paper #1473, p. 99). A common
practice is to multiply the EC in mS·cm-1 by 500
to produce ppm or mg·l-1.
6.2 TYPICAL RANGES
Single distilled water will have an EC of at least
0.001 mS·cm-1. ECs of melted snow usually
range from 0.002 to 0.042 mS·cm-1. ECs of
stream water usually range from 0.05 to 50.0
mS·cm-1, the higher value being close to the EC
of sea water (USGS Water-Supply Paper 1473,
p. 102).
6.3 FACTORY CALIBRATION
The 247 is shipped with a cell constant
calibrated in a 0.01 molal KCl solution at 25.0°C
±0.05°C. The solution has a EC of 1.408 mS
cm-1.

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)]