Operation
2–25
IP244
C79000–B8576–C859–02
3.1.5 Configuring Analog Inputs 0 to 6
Sensors with an output voltage range of 51.2 mV for thermal e.m.f.s or 512 mV for general
applications, can be connected to channels 0 to 6.
3.1.6 Configuring Analog Inputs 7 to 14 (15)
The input channels 7 to 14 (15) have solder lugs on the board to allow shunt resistors for
current measurement or voltage dividers for voltage measurement to be fitted. (When supplied,
a voltage divider 1:400 is fitted for channels 13 and 14, providing an input voltage of 20.48 V at
the ADC sensitivity of 51.2 mV.)
If you wish to change the input range from the factory setting, follow the procedure outlined
below.
Remember that the ADC sensitivity can only be selected for the whole module and that the
sensitivity required for channels 0 to 6 also determines the sensitivity of channels 7 to 14 (15).
To fit the required resistors, the jumpers for R
S
of channels 7 to 12 must be removed.
To obtain the required input voltage (U
I
), the divider ratio of the resistors is calculated as
follows:
Example: U
I
= 10.24 V : ADCĆsens. = 512 mV : R
p
= 2.5 kohms
R
P=
5kohms
R
S
+R
P=
100 kohms
=
U
I
[ mV] R
S
+ R
P
R
p
R
S
=R
P
x
- R
P
ADCĆsens.
U
I
R
S
= 2.5 x 20 - 2.5 = 47.5 kohms
ADCĆsens. [ mV]
Use metal foil resistors with 0.25 W, tolerance 0.1% and a temperature compensation value
(t.c. value) of 50 x 10
–6
or better.
For input currents (e.g. transducer connection with 0 to 20 mA) a jumper must be fitted for R
S
.
The required resistor R
P
is calculated as follows:
R
P
=
I
N
[A]
ADCĆsens. [ V]
Example: I
N
= 20.48 mA; ADCĆsens. = 512 mV
R
P
= 25 ohms
Metal foil resistor 0.25 W, tolerance 0.1 %, t.c. value= 50 x 10
-6
(or better).
R
P
=
0.02048
0.512
= 25 ohms
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