Campbell Scientific 247-L Conductivity and Temperature - Manual (Page 5)

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,
Na
2
SO
4
, NaHCO
3
, 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