IDL 101
FUNCTIONAL DESCRIPTION
HB_IDL101_E_V222.doc
39
Gantner Instruments Test & Measurement GmbH
Measurement of Resistance:
Figure 6.4 Measurement of resistance in 2-wire technique
Figure 6.5 Measurement of resistance in 4-wire technique
Resistance measuring are carried out by means of measurements of voltages at a current-carrying resistor. In this case
the occurring fall of potential is measured via the resistance sensor. The feed current required for the resistance
measuring provides the internal supply of the data logger.
For this purpose the data logger connects a supply point internally with the analog measurement input via a reference
resistor R
o
. The fall of potential U
o
via the resistor R
o
is required as a reference for further signal processing by the data
logger. The value of resistance of the sensor can be calculated from the input signals U
i
as a multiple of the reference
resistor R
o
. The measuring range amounts to between 0 and 2 k
Ω
and for measuring temperature with a Pt 100 sensor
the possible measuring ranges are –40 to +60 °C and –40 to +250 °C.
S
O
U
R
C
E
A
In
+
A
In
-
S
O
U
R
C
E
A
In
+
A
In
-
A
GN
D
A
GN
D
1
2
Connection Scheme
Circuit
Measuring Resistance
R = U / U * R , R = 2 * R
x
1
0
0
x
L
∆
R
x
R
x
R
L
R
0
R
L
SOURCE
A
GND
U
1
U
+
-
S
O
U
R
C
E
A
In
+
A
In
-
S
O
U
R
C
E
A
In
+
A
In
-
A
GN
D
A
GN
D
1
2
Connection Scheme
Circuit
Measuring Resistance
R = (U - U ) / U * R , R = 0
x
2
3
0
0
x
∆
R
x
R
x
R
L
R
0
R
L
SOURCE
AIn +
AIn -
A
GND
U -
2
U
3
U
+
-
