Operation; General Information; Measuring Principle - Siemens SITRANS LR 400 Instruction Manual

Operation

General information

You can operate the SITRANS LR 400 with:
• Local operating and monitoring module
• HART-Communicator or Profibus PA
• PC/Laptop and SIMATIC PDM software (recommended)
Note:
The device can be operated and programmed most comfortably with the
SIMATIC PDM software. This software gives you the added possibility of saving and
archiving your application-specific parameters and copying them back into the device
if necessary.
It is best to perform the operations described in the following sections directly on the
device to familiarize yourself with the operation.

Measuring principle

The SITRANS LR 400 operates according to the FMCW (Frequency Modulated Continuous
Wave) method. Its antenna sends microwaves to the surface of the measuring medium,
the frequency of which is modulated continuously (see "Determining the Differential
Frequency on page 17). A receiver registers the reflection at the surface of the measuring
medium and links it with the simultaneously radiated signal.
The propagation speed of microwaves in gases corresponds to the speed of light. The
d
distance is therefore proportional to the propagation time
d= distance, t = measured time, c = speed of light
Page 16 SITRANS LR 400 – INSTRUCTION MANUAL DRAFT
c t ⋅
d = --------
2
d
t
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