  The ATLAS Tile Calorimeter (TileCal) is the central section of the hadronic
calorimeter of the ATLAS experiment at LHC. This sampling calorimeter uses
steel plates as absorber and scintillating tiles as active medium. The light
produced by the passage of charged particles is transmitted by wavelength
shifting fibers to photo-multiplier tubes (PMTs), located in the outer part of
the calorimeter. The readout is segmented into about 5000 cells, each one being
read out by two PMTs in parallel. To calibrate and monitor the stability and
performance of the full readout chain during the data taking, a set of
calibration sub-systems is used. The TileCal calibration system comprises
Cesium radioactive sources, laser, charge injection elements, and an integrator
based readout system. Combined information from all systems allows to monitor
and to equalize the calorimeter response at each stage of the signal evolution,
from scintillation light to digitization. Calibration runs are monitored from a
data quality perspective and used as a crosscheck for physics runs. Data
quality in physics runs is monitored extensively and continuously. Any problems
are reported and immediately investigated. The data quality efficiency achieved
was 99.6% in 2012, 100% in 2015, 98.9% in 2016 and 99.4% in 2017.
  Based on LHC Run-I experience, all calibration systems were improved for
Run-II. TileCal performance during LHC Run-II, (2015-2017), is discussed,
including calibration, stability, absolute energy scale, uniformity and time
resolution. Results show that the TileCal performance is within the design
requirements and has given essential contribution to reconstructed objects and
physics results.
