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 nor mal use and service for twelve (12) months from date of
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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
i
10. Instruction 11 Details................................................9
11. Electrically Noisy Environments............................10
12. Long Lead Lengths Temperature...........................10
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,
Na
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
, NaHCO3, and/or NaCl, which are typical
2SO4
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.
SOLDER
SIDE
LAC-2
2292
FIGURE 1-1. 247 Conductivity and Temperature Probe
1
247 CONDUCTIVITY AND TEMPERATURE PROBES
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
±10% of reading 0.005 to 0.44 mS cm
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.
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
-1
.
-1
.
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
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.
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.
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