Steam Boiler Applications; Figure 2-13 Typical Echo Steam Application Echo With Vapor Reference Rod - Honeywell SmartLine SLG 700 User Manual

Usually, it will be the material absorption which determines the depth under which the end of
probe will be visible. This can be difficult to predict as published tables might not be correct
especially if there are material impurities or absorbed water present.

Steam Boiler Applications

Sensor revision R200 introduced a new application type: the measurement of the water level in
high-pressure steam boilers.
Unlike regular measurement applications where the user can enter a value for the dielectric
constant of the medium above the liquid, a measurement inside a boiler has a dynamic value of
the dielectric constant which varies with the steam pressure and temperature. To measure the
resulting varying speed of the radar pulse, the measurement rod is extended to include a
reference reflector that sits above the measurement area.
After installation but before the vessel is pressurized, the observed length of the probe to this
reference reflection is measured and recorded by the sensor. During subsequent measurements,
the apparent change in this distance is calculated and used to correct the propagation speed of
the radar pulse.
Steam applications always use the SLG726 (HTHP high temperature high pressure) process
connector with or without the 3-m remote housing extension. In all cases, the sensor uses a
reflection from the HTHP process connector as the reference plane from which all distances are
calculated. In total, therefore, the sensor must have four calibrated reflection models: the
internal reference from the sensor electronics, the process connector reflection mentioned
above, the steam reference reflection and the water surface reflection. While default model
values are supplied for all, it is highly recommended to use the DTM to display a typical echo
and verify that the model amplitudes are set correctly. If possible, verify that the process
connector model is still correct at the boiler operating temperature (amplitude tracking only
tracks level reflection echoes).
A typical example of an echo observed is shown below:

Figure 2-13 Typical Echo steam application echo with vapor reference rod

The transmitter probe type is restricted to coaxial or rod and the mounting location must be either
tank, for coax only, or bypass. In the case of a bypass, the diameter must be specified correctly. Note
the length of the steam reference rod should be calibrated after installation and before the vessel is
pressurized. This can be done from the display module or the DTM or the DD. Background
subtraction is not used for steam applications and it is advised that amplitude tracking be left on.
Revision 8
SLG 700 SmartLine Level Transmitter User's Manual
Page 31