3.3.3.2. DC-Coupled Frequency Configuration Options
Multi-purpose inputs used as frequency inputs allow a periodic waveform with
frequencies ranging from 10 Hz to 10 kHz to be read as a frequency value.
An internal pull-up resistor value of approximately 3.3 k can be turned on or off
for this input type.
The inputs have programmable gain values (1, 3.007, 4.022, 6.029), and
programmable attenuation values (1, 0.3061, 0.1807, 0.1282).
The gain values and attenuation values can be mixed and matched to produce
other gains/attenuation factors.
3.3.3.3. DC-Coupled Frequency Input Connections
When connecting DC-coupled frequency inputs, be aware of system noise and
ground level shift.
System Noise
DC-coupled frequency inputs are more susceptible to system noise than digital
inputs.
To reduce system noise:
Connect DC-coupled frequency inputs to sensors that produce signals with no
DC offset.
Use the shortest possible wires when connecting DC-coupled frequency inputs
to sensors to prevent noise pickup on the sensors.
Ground Level Shift
Ground level shift affects the accuracy of DC-coupled frequency inputs. Ground
level shift refers to the difference between the system ground input (GND)
voltage, and the sensor ground voltage.
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