Ascension laserBIRD, Installation And Operation Manual

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4: Software Operation: Tools for Successful Tracking
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ERROR CODE
When PARAMETERnumber = 10 during EXAMINE, The Bird will output a one byte Error code,
indicating a particular system condition was detected. The byte returned represents the earliest
error code sent to the SYSTEM ERROR register. See the
Error Reporting
section below, for
details.
DC FILTER TABLE Vm
When PARAMETERnumber = 12 during EXAMINE, The Bird returns a 7 word (14 byte) table, or
during CHANGE, the user sends to The Bird a 14 byte table representing the expected noise that
the DC filter will measure. By changing the table values the user can increase or decrease the DC
filter's lag as a function of sensor range from the Scanner.
The DC filter is adaptive in that it tries to reduce the amount of low pass filtering in The Bird as it
detects translation or rotation rates in The Bird's sensor. Reducing the amount of filtering results in
less filter lag. Unfortunately electrical noise in the environment, when measured by the sensor,
may also make it look like the sensor is undergoing a translation and rotation. As the sensor
moves farther and farther away from the Scanner, the amount of noise measured by the sensor
appears to increase because the measured signal level is decreasing and the sensor amplifier gain
is increasing. In order to decide if the amount of filtering should be reduced, The Bird has to know
if the measured events are real due to movement or false due to noise. The Bird gets this
knowledge by the user specifying what the expected noise levels are in the operating environment
as a function of distance from the Scanner. These noise levels are the 7 words that form the Vm
table. The Vm values can range from 1 for almost no noise to 32767 for a lot of noise.
The default values as a function of Scanner to sensor separation range are:
Std. Range Xmtr
Range Vm
(inches) (integer)
0 to 17 2
17 to 22 4
22 to 27 8
27 to 34 16
34 to 42 64
42 to 54 128
54 + 512
As Vm increases with range so does the amount of filter lag. To reduce the amount of lag, reduce
the larger Vm values until the noise in The Bird's output is too large for your application.
DC FILTER CONSTANT TABLE ALPHA_MAX
When PARAMETERnumber = 13 during EXAMINE, The Bird returns 7 words (14 bytes) which
define the upper end of the adaptive range that filter constant ALPHA_MAX can assume in the DC
filter as a function of sensor to Scanner separation. When there is a fast motion of the sensor, the