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5.3.2.
To illustrate the five possible configurations,
the following fluid level measurement settings are
assumed
- To illustrate the five possible configurations, the following fluid level
measurement settings are assumed:
(HyView-
>”Device
Settings”
-
>”Application”
-
>”Operating mode: Liquid level measurement”)
(HyView-
>”Device Settings”
-
>”Measurement Configuration”
-
>”PV source: Level”)
-
Thus, the HART “PV” of the transmitter, its primary digital output, will be a level
value. The level is calculated from the parameter values below:
P03
–
Probe length
P04
–
Zero-level distance
P05
–
Min. distance/Near blocking
P06
–
Max. dist./Far blocking
Other markings in the figure:
R
–
Measuring range
H
–
Tank height
NOTE:
The reference point for
distance measurement “0” is the sealing
flange of the device (bottom of hexagon), the lower surface of the flange for
flanged devices. If max. distance is set to 0, the probe length is the maximum
measuring distance.
The 4…20 mA current output of the level
transmitter can be
assigned to the measured value, HART “PV” with two parameters:
P10: Lower level value: HyView-
>”Device Settings”
-
>”Outputs”
-
>”Assignment of 4
-
mA”)
P11: Upper level value: HyView-
>”Device
Settings”
-
>”Outputs”
-
>”Assignment of 20
-
mA”)
The cases outlined on the right side of the figure above:
1.
The “current output” range is shorter than the max. possible measuring
range: The 4 and 20 mA adjusters are located inside the near and far dead
zone on the probe, within the limits
2.
The range of the 'current output' is equal to the measuring range:
Assignment of 4-
mA (P10): = “0 level” distance –
maximum measuring
distance.
Assignment of 20-
mA (P11): = “0 level” distance –
minimum measuring
distance.
3.
The “current output” range is longer than the measuring range:
Assignment of 4-
mA (P10): = shorter than “0 level” distance –
maximum
measuring distance.
Assignment of 20-
mA (P11): = “0 level” distance –
minimum measuring
distance.
4.
The “current output” range is l
onger than the measuring range:
Assignment of 4-
mA (P10): = “0 level” distance –
maximum measuring
distance.
Assignment of 20-mA (P11): = distance longer
than “level 0” –
minimum
measuring distance.
5.
The “current output” range is
longer than the measuring range:
Assignment of 4-mA (P10): = shorter
than “0 level” distance –
maximum
measuring distance.
Assignment of 20-mA (P11): = distance longer
than “level 0” –
minimum
measuring distance.
5.3.3.
Echo Loss Handling
The reflected signal usually disappears when the level is in the upper dead zone
or near the bottom of the tank.
The zones used to handle signal loss (unreasonably many signals in Zone 1),
which can be adjusted with parameters, are shown in the figure below.
During “
HyView
” polling, the “Device status” function window must be used to
monitor the measurement status of the device on a PC (to activate the function,
see section 5.1.2.3).
It can also be tracked on an VGF-DISPLAY: display.
Indications: “Echo lost”: echo is lost, “E”: tank is
empty, “F”: tank is full, “Echo in
near blocking” in the nearby zone, “Echo in far blocking” in the remote zone.
Zone 1: Detection delay
Calibration setting. It filters out unwanted interferences. It has been
replaced by
the
threshold mask
, which can be edited in the Echo diagram.
It is not recommended!
Since, unlike the threshold mask, the instrument does
not detect any reflections in this section of the probe, regardless of the amplitude!
If the level is in this zone, it can only be inferred from the previous level that the
tank is full.
Zone 2: Close-end blocking: P05
The distance measurement works within the minimum measuring distance, up to
the detection delay. If the level is closer when switched on, the minimum
measuring distance (or the values calculated from it) is returned, “F” is displayed
as full and “Echo in near blocking” is displayed. For Eview 2 polling, “Echo in near
blocking” is also passed. The same is true if the echo of the level is transferred to
this range from the actual measurement zone.
