Vansco VMM3120, Руководство пользователя

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26 VMM3120
Inputs
3.3.2.3. 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.
To reduce ground level shift:

If there are more than 1 GND pins in the system, dedicate one of them to
sensors that have ground wires, and connect all sensor grounds to that system
ground pin.

Splice the other system ground inputs together in the vehicle harness (close to
the connector), to provide a better ground for the noisier low-side outputs and
digital circuits.
 Ensure the sensor’s ground connection is close to the system ground
connections. This will help ensure the signal remains within the digital
activation range of the input.
Note 1: The VMM3120 system ground inputs are rated for low-current
signals, which ensures the sensor’s ground is very close in voltage potential to
the system ground.
Note 2: Sensors that don’t have a dedicated ground wire are typically
grounded to the vehicle chassis through the sensor’s body.