Reference Manual
00809-0100-4731, Rev FA
April 2003
3-3
APEX
™
and APEX Sentry
™
Radar Gauge
The Reference Gauge Height is the distance between the reference line and
the face of the radar gauge flange, as shown in Figure 3-1. The Reference
Gauge Height is the most critical setting for the radar gauge because it is the
basis for all other calculations. The radar gauge measures the distance to the
product surface and subtracts this value from the Reference Gauge Height to
determine level. To keep level measurements within the stated accuracy
specifications, the Reference Gauge Height must be within the ranges
specified in Appendix A: Reference Data.
If the distance from the reference line (bottom) of the vessel to the gauge is
unknown, you can do one of the following:
• Record the radar gauge level reading and compare it to another known
reference level measurement, such as a hand dip.
Enter the actual level during the configuration process
(see Section 2: Installation). The actual level and distance equals the
Reference Gauge Height. Use the distance reading from the gauge
and the actual level measurement from some other means, add these
values, and input the sum on the Reference Gauge Height.
or
• If the radar gauge is installed when the tank is empty, measure the
Reference Gauge Height (see Figure 3-1) and record the value. You
can determine the Reference Gauge Height in one of
two ways:
– Use the engineering drawing of the vessel to calculate the distance
from the mounting flange surface to the bottom of
the tank.
– If the tank has a flat bottom, use the HART Communicator to set
Distance as the secondary variable and have the radar gauge measure
it. The distance reading displayed on the HART Communicator is the
Reference Gauge Height.
Minimum Clearance to Product Level
The minimum clearance from the gauge flange to the expected maximum
product level must be at least 19.6 inches (50 cm). The gauge cannot
accurately measure levels at less than 19.6 inches (50 cm) from the flange.
Maximum Range
The maximum measuring range for stated accuracies can be found in
Section A: Reference Data.
Upper Range Value (20 mA Point)
When configuring the gauge, you must provide the Upper Range Value
(URV). The URV must be at least 19.6 inches (0.5 m) above the lower range
value.
Lower Range Value (4 mA Point)
When configuring the gauge, the Lower Range Value (LRV) must be provided
and must be at least 19.6 inches (0.5 m) below the upper range value.
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