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Note
Prior to board revision 186307G-01L, the internal resistor value on the
encoder input circuit was 1 kΩ. Figures 3-2 and 3-3 show the location of the part
number label on PXI and PCI boards, respectively. For earlier versions of the
NI 7340, refer to the NI 7340 User Manual and Specifications document,
370838A-01, November 2003 revision.
Caution
component failure. Verify that the input voltage is within the specification range.
Encoder Signals
The NI 7340 motion controller offers four 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.
Encoder <1..4> 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 or velocity monitoring, digital potentiometer encoder inputs, or as a master encoder
input for master/slave (electronic gearing) applications.
The encoder channels (Encoder <1..4>) are implemented in an FPGA and are high performance
with extended input frequency response and advanced features, such as high-speed position
capture inputs and breakpoint outputs.
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 two signals, 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 of measure (revolutions
or linear distance) produces 4 × N quadrature counts per unit of measure. The count is the basic
increment of position in NI-Motion systems.
Tip
Determine quadrature counts by multiplying the encoder resolution in encoder
lines by four. The encoder resolution is the number of encoder lines between
consecutive encoder marker or Z-bit indexes. If the encoder does not have an index
output, the resolution is referred to as lines per revolution, or lines per unit of
measure, such as inch, centimeter, millimeter, and so on.
Excessive input voltages can cause erroneous operation and/or
NI 7340 User Manual and Specifications
© National Instruments | 4-7
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