Dear Amirul,
These are basic Instrumentation Terms and the main source of such teminology is the Standard ISA S 5.11: Process Instrumentation Terminology.
Sourcing from above your mentioned terms mean as follows:
lrl= lower range-limit: The lowest value of the measured variable that a device can be adjusted to measure.
url= upper range-limit : The highest value of the measured variable that a device can be adjusted to measure.
lrv= lower range-value: The lowest value of the measured variable that a device is adjusted to measure.
urv= upper range-value: The highest value of the measured variable that a device is adjusted to measure.
Regards,
Sajid Ali Khan
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