Vansco VMM3120, User Manual, Page: 31 / 92

User Guide 21
Inputs
The following shows how to address ground shift with sensors that do not have
dedicated ground wires:
Figure 10: Analog input with ext. pull-up for sensors without ground wire
3.3. Frequency Inputs
Frequency inputs are typically used to read pulse signals.
There are two types of frequency inputs in the VMM3120:

AC-coupled frequency inputs

DC-coupled frequency inputs
3.3.1. AC-Coupled Frequency Inputs
The VMM3120 has 2 AC-coupled frequency inputs:

FREQ_1

FREQ_2
3.3.1.1. AC-Coupled Frequency Input Capabilities
AC-coupled frequency inputs provide AC-coupling, which allows you to read the
frequency of external signals that have either large DC offsets, or no ground
reference. These inputs are ideal for use with variable reluctance and inductive
pickup sensors.