Kipp&Zonen COMBILOG Data Logger - Manual (Page 41)

5.1.3 Resistance Measurement
Resistance measurement is carried out by means of voltage
measurement at a resistor, measuring the resulting voltage
drop. The constant current required for the resistance meas-
urements is provided by the internal supply of the data logger.
For this purpose the sensor module connects a supply point in-
ternally with the analogue measurement input via a reference
resistor R
o
. The voltage drop U
o
via resistor R
o
is required as a
reference for further signal processing by the module. The res-
istance value of the sensor can be calculated from the input
signals U
i
as a multiple of the reference resistor R
o
. Measuring
range is between 0 and 20 k Ω .
Note: The data logger COMBILOG 1022 supports resistance
measurement in 2-, 3- and 4-wire technique. With resistance
measurement in 2-wire technique the supply lines cause an ad-
ditional voltage drop, thus distorting the measuring result and
influencing the measuring accuracy. Therefore it is necessary
to pay attention especially with resistance measurement in 2-
wire-technique. Wires with impedance as low as possible
should be used. Make sure that the leads are well connected to
the data logger and the sensor. With resistance measurement
using 3-wire technique the potential on the supply lines will be
subtracted by software. Therefore 2 measurements are neces-
sary, resulting in double measuring time. With resistance
measurement in 4-wire technique the drop of potential is picked
up directly at the sensor, so that the measuring results are not
influenced by the supply lines.
Hardware Manual COMBILOG 1022
41