User's Manual

Page 132 SITRANS LR250 (HART) – INSTRUCTION MANUAL 7ML19985JE03
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D: Technical Reference
Damping
Damping Filter (2.2.4.) smooths out the response to a sudden change in level. This is an
exponential filter and the engineering unit is always in seconds.
In 5 time constants the output rises exponentially: from 63.2% of the change in the first
time constant, to almost 100% of the change by the end of the 5th time constant.
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%.
When SITRANS LR250 is put into PROGRAM mode (for example, by navigating through
the menu) it stops updating the output of the device (local user interface and mA Output).
It stores the most recent measurement, and holds the associated readings and mA signal
output. The device reverts to the parameter last addressed during the previous program
session.
When the device is returned to Measurement mode, the transceiver resumes operation.
The reading and mA output default to the last measurement taken. The reading and
associated outputs migrate to the current process level at a rate controlled by Response
Rate (2.4.1.).
If the device is left in PROGRAM
mode for 10 minutes without input, it automatically
reverts to Measurement mode.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
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Series1 Series 2
Level (m)
Time (s)
smoothed output
input (level)
Damping example
time constant = 2 seconds
input (level) change = 2 m