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2.2.1.1
Input
Conditioning
2.2.2
Zero Crossing
Detection
2.2.2.1
Dual VR IC
© Copyright 2024
United Electronic Industries, Inc.
•
TTL-level digital pulse train - Some sensors, such as Hall Effect
sensors, already output a conditioned 0-5 V square wave.
•
Revision 1: The digital sensor's signal and return wires connect to
a single VR-608 channel (e.g., In
power wire does not connect to the VR-608.
•
Revision 2: The digital sensor can either connect to a VR-608
channel or connect directly to a counter/timer module through DIn/
DIGnd. The direct DIn connection is the recommended configuration
as it bypasses the zero crossing and peak threshold stages for a
faster read rate.
All VR analog inputs pass through a limiter circuit before entering the Dual VR
IC and ADCs.
Revision 2 boards provide a digital FIR filter after each ADC to smooth out noise
on the VR inputs. It is useful when the ADC tooth rate is greater than 10 kHz. By
default, the FIR filter is disabled. It may be enabled in board configuration.
Zero crossing detection is performed by either the Dual VR IC (default) or the
channel's ADC. The ADC input path is highlighted in blue in Figure 2-5.
The DNx-VR-608 supports the following zero crossing modes:
•
VR608_ZC_ONCHIP: automatically determines the mid-range of the
analog sine wave signal using the built-in zero-cross detector of the
Dual VR IC.
•
VR608_ZC_FIXED: fixed to a particular voltage level by the user and
detected by the ADC module. If the desired zero crossing level is 0 V,
UEI recommends setting the desired zero crossing level to a value
slightly above 0 to avoid false positives, e.g., 0.1 V.
•
VR608_ZC_LOGIC: calculated by the ADC module as (min+max)/2,
subject to a configurable moving average.
Because the Dual VR IC expects a bipolar input, Hall Effect sensors and other
unipolar digital inputs should use an ADC-based mode (ZC_FIXED OR
ZC_LOGIC). ADC-based modes cap the input pulse rate at 18 kHz.
DIn connections will use VR608_ZC_ONCHIP by default. This is the
recommended configuration. Using VR608_ZC_ONCHIP mode is also
recommended with analog inputs.
The Dual VR IC's purpose is to convert the VR sensor's analog signal into a
digital output. The Dual VR IC electronic chip is the Maxim MAX9926 Variable
Reluctance Sensor Interface.
Figure 2-6 takes a closer look at the logic for one channel in the Dual VR IC.
After the input signal has passed the limiter circuit, it enters the Dual VR IC and
is clipped from ±125 V down to ±5 V using Zener diodes. The ±5 V input is
amplified before entering the zero crossing detection circuit.
The zero crossing circuit centers around an inverting comparator. The
reference voltage at the comparator's non-inverting (+) terminal switches
between the zero crossing level and a configurable peak threshold level
depending on the current state of the comparator output (cout). When cout is
low, the input is compared to the zero crossing level to determine when cout
should be raised. When cout is high, the input is compared to the peak
February 2024
DNx-VR-608 Variable Reluctance Interface
Functional Description
+/- of Channel 0); the sensor's
0
Chapter 2
13
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508.921.4600
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