Siemens SITRANS LUT400, Руководство по эксплуатации

Страница: 576 / 601

A5E33329501 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS Page 263
mmm
mm
App. A -
Te
c
hni
cal Ref
.
Analog Output
The mA output (current output) is proportional to material level in the range 4 to 20 mA.
0% and 100% are percentages of the full-scale reading (m, cm, mm, ft, in). Typically mA
output is set so that 4 mA equals 0% and 20 mA equals 100%.
Current Output Function (2.5.1.)
Current Output Function (2.5.1.) controls the mA output and applies any relevant scaling.
By default it is set to LEVEL. Other options are Space, Distance, Volume, Head, Flow, or
Manual. A MANUAL setting allows you to test the functioning of the loop.
You can also set the mA output to report when the device is in an error condition and the
fail-safe timer has expired. By default, the reported value depends on the device type. A
standard device reports the last valid reading, and a NAMUR NE43 compliant device
reports the user-defined value for Material Level (3.58 mA by default).
Loss of Echo (LOE)
A loss of echo (LOE) occurs when the calculated measurement is judged to be unreliable
because the echo confidence value has dropped below the echo confidence threshold.
If the LOE condition persists beyond the time limit set in LOE Timer (2.4.2.) the LCD
displays the Service Required icon, and the text region displays the fault code 0 and the
text LOE.
If two faults are present at the same time, the device status indicator and text for the
highest priority fault will display. For example, if both Loss of Echo and Broken cable
faults are present, the Broken cable fault will display.
1 Broken cable
Fail-safe Mode
The purpose of the Fail-safe setting is to put the process into a safe mode of operation in
the event of a fault or failure. The value to be reported in the event of a fault (as displayed
in
2.5.8. Current Output Value
) is selected so that a loss of power or loss of signal triggers
the same response as an unsafe level.
LOE Timer (2.4.2.) determines the length of time a Loss of Echo (LOE) condition will persist
before a Fail-safe state is activated. The default setting is 100 seconds.
Material Level (2.4.1.) determines the mA value (corresponding to the selected PV) to be
reported when LOE Timer (2.4.2.) expires. The default setting is device dependent
(standard or NAMUR NE 43-compliant).
Upon receiving a reliable echo, the loss of echo condition is aborted, the Maintenance
Required icon and error message are cleared, and the mA output return to the current
material level. [The PV region on the LUI display will show dashes (– – – – – – –) when a
fault that causes fail-safe is present, and will return to the current reading when the fault
is cleared.]