Campbell Scientific CS547A-L Conductivity/Temperature Probe and A547A Interface - Manual (Page 7)

CS547A Conductivity and Temperature
Probe and A547 Interface
1. Overview
The CS547A conductivity and temperature probe, and A547 interface are
designed for measuring the electrical conductivity, dissolved solids, and
temperature of fresh water with Campbell Scientific dataloggers. This sensor
can be used with any CSI logger that can issue a negative excitation. This
includes most new CRBasic dataloggers as well as older, Edlog loggers.
Exceptions include the CR200-series, the BDR301 and BDR320 loggers which
did not have this feature. Use with our AM16/32(B) multiplexer is possible
when needing to measure several of these probes on one datalogger.
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 CS547A. 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 in the tube is measured by
excitation of the center electrode with positive and negative voltage.
This electrode configuration eliminates the ground looping problems
associated with sensors in electrical contact with earth ground.
Temperature is measured with a thermistor in a three wire half bridge
configuration.
1.2 A547 Interface
The interface contains the completion resistors and blocking capacitors. The
interface should be kept in a non-condensing environment that is maintained
within the temperature range of the unit.
1