A5E33329501 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS Page 99
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General Operation
Setting Zero Head
Many PMDs start flowing higher than the traditional empty distance of the application.
You can account for the flow in one of two ways:
1. Use
2.15.3.5. Zero Head Offset
to have OCM calculations ignore levels below that
value. Possible head =
2.2.1. Low Calibration Point
minus
2.2.2. High Calibration Point
.
2. Use
2.2.5. Far Range
where the empty level is set to the bottom of the weir, and
above the bottom of the channel. It should be used if the surface monitored can fall
past the
2.2.1. Low Calibration Point
level in normal operation without reporting an
LOE. The value is added to
2.2.1. Low Calibration Point
and can be greater than the
range of the transducer.
The examples on the following pages show both methods.
Note:
2.15.3.3. Maximum Head
is preset to
2.2.1. Low Calibration Point
minus
2.2.2.
High Calibration Point
and is not updated when
2.15.3.5. Zero Head Offset
is used.
Make sure you set
2.15.3.3. Maximum Head
to the correct value when using
2.15.3.5.
Zero Head Offset
. (Refer to PMD supplier documentation for Maximum Head.).
zero head
max. head
low cal. point
high cal. point
far
range
head
sensor ref. point
material surface
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