Open Channel Monitoring (Ocm); Failsafe - Siemens SITRANS Probe LU Operating Instructions Manual

Open Channel Monitoring (OCM)

OCM converts a level reading (head) into a flow value using a linear algorithm.
SITRANS Probe LU can convert a head level measurement into a flow rate, using a thirty-
two breakpoint head-versus-flow characteristic curve. This chart is usually available
from the manufacturer of the v-notch weir, Parshall flume, or other open channel device.
Parameter P050 must be set to 9 (universal linear function), and breakpoints must be set
for head levels and corresponding flowrates at parameters P054 and P055. Once these
parameters are set, the mA output is scaled to represent the flowrate, and the RUN mode
display will show the flowrate
Example: Flow Characterization.
11
10
9
8
7
6
5
4
3
2
1
1 2
The maximum and minimum points on the curve must be defined. Then program the
remaining breakpoints to closely match the flow curve of your open channel device.

Failsafe

The Failsafe function can be activated either if there is not a valid measurement, or by
one of the faults marked by an asterisk in the table
Failsafe mode, the device will output one of the four options determined by P071 (Failsafe
Material Level).
Failsafe Mode P071
1 = HI
2 = LO
3 = HOLd
4 = SEL
A5E32337695 SITRANS Probe LU (HART) – OPERATING INSTRUCTIONS
3 4 5
head (P054)
Use Maximum mA Limit (P213) as material level
Use Minimum mA Limit (P212) as material level
Level remains at last reading
User-selected value (defined in P073)
6 7 8 9
General Fault Code
10 11
on page 82. In
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