Data Sheet

Page 8 ams Datasheet
Document Feedback [v1-01] 2015-Oct-12
AS-MLV-P2 − Application I nfo rmation
The resolution of the measurement of R
S
is recommended to
be better or equal to 1% of the actual reading. This allows
making use of the full performance of the sensor. The
requirements for the A/D conversion of the output voltage V
out
is described in the following section.
The input impedance of the A/D converter should be high
enough not to influence the level of the voltage divider, a ration
of at least 10 between input impedance and values of R
S
and/or
R
L
is recommended.
Averaging A/D conversion procedures are recommended in
order to suppress fast resistance changes from the sensitive
layer (resistive noise and change of the resistance due to
chemical influences).
In order to achieve 1% of precision of the read-out of R
S
, the
A/D conversion of V
out
needs lower resolution, if sensor- and
load resistor match. A larger difference between R
S
and R
L
requires a higher resolution of the A/D conversion. The
following figure gives a few examples for V
S
= 5V.
Figure 9:
Examples for Readout of R
S
with 1% Resolution (V
S
=5V)
Examples for Readout of R
S
with 1% Resolution: The series resistor R
L
has also the functionality to limit the
power dissipated to the sensitive layer.
If the A/D conversion is single ended (common ground) it might
be useful to change the sequence of load resistor and sensor
resistor in the voltage divider. This enables to increase the
resolution by using a lower reference voltage for the A/D
conversion.
R
S
[Ohm] R
L
[Ohm] V
out
[V]
A/D Voltage Step for 1% Resolution
100 10k 4.95 0.5mV
1k 10k 4.5454 4.1mV
10k 10k 2.5 12.4mV
100k 10k 0.4545 4.1mV
1M 10k 0.0495 0.5mV
1k 100k 4.95 0.5mV
10k 100k 4.5454 4.1mV
100k 100k 2.5 12.4mV
1M 100k 0.4545 4.1mV