Chapter 5 Signal Connections
NI 7350 User Manual 5-8 ni.com
Caution Excessive input voltages can cause erroneous operation and/or component
failure. Verify that the input voltage is within the specification range.
Encoder Signals
The NI 7350 controller offers up to eight channels of single-ended
quadrature encoder inputs. All National Instruments power drives and UMI
accessories provide built-in circuitry that converts differential encoder
signals to single-ended encoder signals. Each channel consists of a
Phase A, Phase B, and Index input, as described in the following sections.
Axis <1..8> Encoder Phase A/Phase B
The encoder inputs provide position and velocity feedback for absolute
and relative positioning of axes in any motion system configuration.
If an encoder resource is not needed for axis control, it is available for other
functions including position monitoring, digital potentiometer encoder
inputs, or as a master encoder input for master/slave (electronic gearing)
applications.
The encoder channels (Axis <1..8> Encoder Phase A/Phase B) are
implemented in an FPGA and provide advanced features, such as
high-speed position capture inputs and position breakpoint outputs. The
encoders have a maximum count frequency of 20MHz.
An encoder input channel converts quadrature signals on Phase A and
Phase B into 32-bit up/down counter values. Quadrature signals are
generated by optical, magnetic, laser, or electronic devices that provide
twosignals, Phase A and Phase B, that are 90° out of phase. The leading
phase, A or B, determines the direction of motion. The four transition states
of the relative signal phases provide distinct pulse edges that cause count
up or count down pulses in the direction determined by the leading phase.
A typical encoder with a specification of N (N = number) lines per unit
ofmeasure, which can be revolutions or linear distance, produces 4 × N
quadrature counts per unit of measure. The count is the basic increment of
position in National Instruments motion systems.
Note If your encoder does not supply resolution in quadrature counts per revolution,
determine quadrature counts per revolution by multiplying the encoder resolution, in
encoder lines or periods, by 4. The encoder resolution is the number of encoder lines
between consecutive encoder indexes, such as marker or Z-bit. If the encoder does not have
an index output, the resolution is referred to as lines per revolution, or lines per unit of