Configuring a Module for Quadrature Input (Scan Interface)

CompactRIO Reference and Procedures Scan Interface

Edition Date: July 2010

Part Number: 372603F-01

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You can configure a digital input module for quadrature input. A quadrature input returns position and velocity data based on the values of three channels. In quadrature input mode, channels 0, 1, and 2 are the A, B, and Index channels, respectively, of Quadrature0. If the module has six or more channels, channels 3, 4, and 5 can form a second quadrature input, Quadrature1. A C Series module can have only two quadrature inputs. Quadrature inputs return position data in counts and velocity in counts per second. You can configure the following options for quadrature input.

Input Filter

You can add an input filter to all input channels of the module. A filter removes noise, glitches, and spikes on inputs by rejecting signals with periods shorter than the specified length. You can select one of the following options.

  • Disabled—The hardware synchronizes the digital inputs using a 4 MHz timebase. Pulses longer than 250 ns are always detected. Pulses shorter than 250 ns may be rejected.
  • 1 µs—Pulses shorter than 1 µs are rejected. Pulses between 1 µs and 2 µs are sometimes detected. Pulses longer than 2 µs are always detected.
  • 16 µs—Pulses shorter than 16 µs are rejected. Pulses between 16 µs and 32 µs are sometimes detected. Pulses longer than 32 µs are always detected.
  • 256 µs—Pulses shorter than 256 µs are rejected. Pulses between 256 µs and 512 µs are sometimes detected. Pulses longer than 512 µs are always detected.
  • 4096 µs—Pulses shorter than 4096 µs are rejected. Pulses between 4096 µs and 8192 µs are sometimes detected. Pulses longer than 8192 µs are always detected.

Velocity Timebase

Selecting a Velocity Timebase is a tradeoff between resolution and response speed. A shorter timebase provides lower resolution but the data it returns is more up to date. A longer timebase provides higher resolution but may lag behind or miss changes in velocity.

  • 256 µs—The counter returns the number of counts that occur in 256 µs. Use this setting for velocities of 500,000 counts/s or faster.
  • 512 µs—The counter returns the number of counts that occur in 512 µs. Use this setting for velocities of 250,000 counts/s or faster.
  • 1024 µs—The counter returns the number of counts that occur in 1024 µs. Use this setting for velocities of 125,000 counts/s or faster.
  • 2048 µs—The counter returns the number of counts that occur in 2048 µs. Use this setting for velocities of 62,500 counts/s or faster.
  • 4096 µs—The counter returns the number of counts that occur in 4096 µs. Use this setting for velocities of 31,300 counts/s or faster.
  • 8192 µs—The counter returns the number of counts that occur in 8192 µs. Use this setting for velocities of 15,600 counts/s or faster.
  • 16384 µs—The counter returns the number of counts that occur in 16384 µs. Use this setting for velocities of 7,800 counts/s or faster.
  • 32768 µs—The counter returns the number of counts that occur in 32768 µs. Use this setting for velocities of 3,900 counts/s or faster.

Index Mode

If you enable an Index Mode, the position is reset to zero when A and B have the specified values and the Index is in the on state.

  • Disabled—The position is never reset to zero.
  • Phase B0 A0—The position is reset to zero when B and A are both in the off state and the Index is in the on state.
  • Phase B0 A1—The position is reset to zero when B is in the off state and A and the Index are both in the on state.
  • Phase B1 A0—The position is reset to zero when B is in the on state, A is in the off state, and the Index is in the on state.
  • Phase B1 A1—The position is reset to zero when A, B, and the Index are all in the on state.

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