User's Manual

Appendix A: Technical reference
A.3 Analog Output
SITRANS LR250 (HART)
224 Operating Instructions, 01/2014, A5E32220602-AB
A.2.9
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.
Damping example
time constant = 2 seconds
input (level) change = 2 m
A.3
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.