User Manual
PLUS System Manual System Installation 39
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2.5 System Calibration
The following section describes the process of calibrating the PLUS system. The purpose of
calibration is to remove the time delays introduced by the varying length cables run to each Reader.
Because the Location Engine calculations are based on the Tag signal time of arrival to each Reader,
it is necessary to remove these additional timing delays to produce accurate location results.
With the 2.0 SDP and Readers, it is only necessary to calibrate the system one time as long
as no changes are made to the installation.
Do run a new calibration if Readers are added or replaced, or if cables are replaced.
Do not run a new calibration if the Readers or SDP are power cycled. The system will retain its
calibration through a power outage.
With the introduction of Reader groups in release 2.0 of the Location Engine, you can calibrate
groups all at once, or one at a time. This enables you to calibrate and verify the system by working
with a few Readers at a time. Two scenarios to illustrate calibration options are described below. In
each scenario, we will assume the same building layout and an installation consisting of fifty Readers.
Scenario 1: The fifty Readers are treated as a single group. Twenty tags are designated as calibration
tags, and are surveyed and permanently mounted in the facility. If a cable is replaced, it is necessary
to recalibrate all fifty Readers. Once a calibration has been configured (as explained in the following
paragraphs), it is easy to recalibrate using permanently mounted tags . The user must take care that
the environment does not change (people and equipment do not introduce blockage between the
calibration tags and readers) or errors could be introduced into the calibration.
Scenario 2: The fifty Readers are partitioned into five groups, averaging ten Readers each. Two
calibration tags are used to calibrate the system by surveying temporary locations and calibrating the
system one group at a time. If a cable is replaced, it is only necessary to recalibrate the groups
containing the affected Readers. The other groups can continue operating normally and generating
locations without disruption. Recalibrating the affected groups requires replacing the calibration tags
in their surveyed locations, or performing a new survey.
Note that the choice of permanently mounting calibration Tags verses temporarily placing Tags is
independent of the choice of one group verses multiple groups. The user is free to choose the best
approach for a given environment and system usage.
2.5.1 Calibration Tag Placement
Calibration Tags are standard PLUS Asset Tags that are placed in surveyed locations to help calibrate
the system. After the calibration process is complete, the Tags may be removed from the installation
area and used as standard Asset Tags. If one or more groups are recalibrated, the Tags serving those
groups must be returned to their surveyed locations. Leaving the tags in their surveyed locations also
has the advantage of providing a known Tag location for assessing performance of the system.
For the system to calibrate properly, all Readers must hear one or more Calibration Tags. In addition,
each Reader in a group must be able to ―stitch‖ their results to all other Readers in the same group by
hearing a common set of tags. For example, in Figure 2-30, Readers 1, 2 and 3 can hear Calibration
Tag A, and Readers 4 and 5 can hear Calibration Tag B. These five Readers cannot be calibrated
because there is no overlap with the Calibration Tags. In Figure 2-31 Tag B has been relocated so
that Reader 2 can hear it. This group of Readers will now calibrate.