National Instruments FP-QUAD-510 Velocity Data Channel Operation

You can configure each position counter to reset each time the

index condition is met. An index-initiated reset resets both the

upper and lower 16-bit registers associated with that axis. This

isuseful in applications in which only the position within one

rotation of the encoder is important to the user. In this mode of

operation, any count errors that occur are canceled when the index

condition is met.

Channels 0 through 3 (the lowest 16 bits of the position counter)

each support a control command with one action—reset. The

control-reset command resets the target counter. The control

command ignores the index reset setting. This command also resets

the upper 16 bits of the position counter.

Velocity Data Channel Operation

The FP-QUAD-510 uses a timebase counter as a basis for

determining the rate of change of position—the velocity—for each

axis. The four velocity data registers, channels 8 through 11,

contain 16-bit velocity data for axes 0 through 3 respectively. The

data in each register represents the velocity of the axis in number

of counts per microsecond. A positive number indicates motion in

the forward direction, and a negative number indicates motion in

the reverse direction. Each register can be independently

programmed with one of eight velocity ranges as shown in Table2.

Each range is based on a different timebase length and has a

different resolution.

Note While the ranges available reach speeds of

160counts per microsecond, the module inputs are still

limited to 1,000,000 counts per second (1 count per

microsecond) maximum. The higher ranges are used to

measure velocity over shorter timebases. With these

ranges, the velocity data is averaged over a much shorter

time period and, therefore, is more instantaneous.

However, the data from these ranges has a coarser

resolution. The slower ranges have a finer resolution, but

the data is an average velocity over a longer period

oftime.