X20 system modules • Analog input modules • X20AI2237
X20 system User's Manual 3.10
159
4.3.4.9.3 General information
The X20AI2237 provides two electrically isolated channels. Each channel can read an electrical voltage signal in
the ±10 V range, and the supply the signal encoder with 24 VDC.
4.3.4.9.4 Analog input - Configuration
Each channel is configured and enabled separately First, the user must set the
scaling
of the input value and select
a
replacement value strategy
. Depending on the requirements of the application, the user can also set
user-defined
limit values
to limit the
slew rate of the input value
.
Scaling
The module's ADC works at a resolution of 16 bits (±15 bits). This allows the input value of ±10 V to be mapped
using ±32767 steps. To simplify implementation, the user can configure scaling to ±10000 steps. The conversion
value corresponds to the voltage in mV, and with a resolution of more than 14 bits (±13 bits) is still precise enough
for the many different application that use this technology.
Replacement value strategy
The detected voltage is evaluated in order to ensure the quality of the read value. For example, if a logically
impermissible voltage value or an open line is detected, the limit monitor triggers an appropriate response.
The response is determined by the replacement value strategy selected by the user. With the option "Replace with
static value", the user defines two values that replace the converted value when the upper and lower limits are
exceeded. The alternative "Retain last valid value" keeps the last validated value. However, the evaluation for this
option takes more time. Depending on the defined preparation interval, the currently read value may be delayed.
User limit check
In addition to the qualitative evaluation of the input, the module also provides the option of adapting the range
of permitted values to the requirements of the application. The "UpperLimit" and "LowerLimit" registers can be
used to place additional restrictions on the permitted upper and lower limit. When this feature is used, the selected
replacement value strategy is implemented according to the new limits.
Slew rate of the input value
Analog input signals can experience brief disturbances caused by external factors (EMC). The ADC's high sampling
rate allows you to filter out these types of signal peaks without hindering the application processes.
Two configuration points are available for interpolating the input signal:
•
"Level of input filter" and
•
"Input limitation"
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