Setting Zero Head - Siemens SITRANS L 7ML5400 Operating Instructions Manual

7.11.3

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 Zero Head Offset (2.15.3.5.) (Page 237) to have OCM calculations ignore levels below
that value. Possible head = Low Calibration Point (2.2.1.) (Page 176) minus High Calibration
Point (2.2.2.) (Page 176).
Note
Maximum Head (2.15.3.3.) (Page 237) is preset to Low Calibration Point (2.2.1.)
(Page 176) minus High Calibration Point (2.2.2.) (Page 176) and is not updated when Zero
Head Offset (2.15.3.5.) (Page 237) is used. Make sure you set Maximum Head (2.15.3.3.)
(Page 237) to the correct value when using Zero Head Offset (2.15.3.5.) (Page 237).
(Refer to PMD supplier documentation for Maximum Head.).
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2. Use Far Range (2.2.5.) (Page 177) 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 Low Calibration Point (2.2.1.) (Page 176) level in normal operation without
reporting an LOE. The value is added to Low Calibration Point (2.2.1.) (Page 176) and can be
greater than the range of the transducer.
The examples on the following pages show both methods.
SITRANS LUT400
Operating Instructions, 04/2021, A5E33329501-AG
Sensor reference point
High calibration point
Low calibration point
Far range
Zero head
Head
Material surface
Maximum head
General Operation
7.11 Open Channel Monitoring (OCM)
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