Vansco VMM3120, User Manual

Page: 32 / 92

22 VMM3120
Inputs
Note: Quadrature and pulse counting is possible; however, we recommend to
not use these functions with AC-coupled frequency inputs.
The following table provides specifications for the VMM3120's AC-coupled
frequency inputs:
AC-Coupled Frequency Input Specifications
Item MIN NOM MAX UNIT
Input voltage range -90 - 90 V
Pull-up resistance (24 V system) 4.7 k - -
Ω
Accuracy - - 5 %
Frequency range @ 2.5 Vp-p 1 - 10000 Hz
Frequency range @ 0.25 Vp-p 3 - 850 Hz
3.3.1.2. AC-Coupled Frequency Input Configuration
The pull-down or pull-up resistors for AC-coupled frequency inputs can be
enabled or disabled; however, they cannot be enabled at the same time. The pull-
up and pull-down resistance is 3.3 k

.
3.3.1.3. AC-Coupled Frequency Input Connections
When connecting AC-coupled frequency inputs, be aware of system noise and
ground level shift.
System Noise
AC-coupled frequency inputs are more susceptible to system noise than digital
inputs.
To reduce system noise:

Connect AC-coupled frequency inputs to sensors with significant DC offset.

Use the shortest possible wires when connecting AC-coupled frequency inputs
to sensors to prevent noise pickup on the sensors.
Ground Level Shift
Ground level shift affects the accuracy of AC-coupled frequency inputs. Ground
level shift refers to the difference between the system ground input (GND)
voltage, and the sensor ground voltage.