Vansco VMM3120, User Manual

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User Guide 19
Inputs
The following shows how to connect analog inputs to reduce system noise:
Internal to product
+5 Vdc Sensor Supply
Sensor Ground
Sensor
Analog Input
Figure 8: Analog input system noise reduction
Ground Level Shift
The accuracy of analog inputs can be affected by ground level shift. Ground shift
refers to the difference between the system ground voltage (system ground inputs
are called GROUND) and the sensor ground voltage.
There are two kinds of sensors need to be addressed: sensors that have dedicated
ground wires and sensors that don't have dedicated ground wires.
To reduce ground level shift for sensors that have dedicated ground wires

Dedicate one of the five system ground inputs (GROUND) to sensors that
have dedicated ground wires, and connect all sensor grounds to this system
ground input.

Splice the other four 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: The VMM3120 system ground inputs are rated for low-current signals,
and ensure the sensor's ground is very close in voltage potential to the
VMM3120 ground.