 | Behaviour of \AvDeltaHV{} as a function of time of a stable (left) and an unstable channel (right) observed during the 2015 run. |
 | The noise filter inserted in the connectors between the HVopto board and the input of each PMT voltage divider. |
 | Comparison of the PMT gain variation measured by the Laser and computed using the monitored high voltage {\HVmeas} in the case of the stable channels PMT 15 of the module LBC08 (left) and PMT 46 of the module LBC08 (right). By definition, the first point is set to zero. |
 | Comparison of the PMT gain variation measured by the Laser and computed using the monitored high voltage {\HVmeas} in the case of channels with faults in the regulation loop systems: PMT 43 of the module LBA20 (left) and PMT 26 of the module LBC51 (right). By definition, the first points are set to zero. |
 | Two partial views of the external HVbus board. In the top one can see the low and high voltage input connector (1) and several connectors feeding the HV to the PMTs, among them the one of PMT 44 is indicated with (2). The picture in the bottom shows several HV connectors linking the HVopto board to the HVbus board (for example the one indicated with (3)). The connector (4) links the external HVbus board with the internal HVbus board through the HVflex (see Fig.~\ref{fig:diagram}) that does not appear in the picture. |
 | Scheme of the HV distribution system. In the HVopto board the odd and even components correspond to the left and right PMTs respectively discussed in the text. |
 | Behaviour of \AvDeltaHV{} as a function of time of a stable (left) and an unstable channel (right) observed during the 2015 run. |
 | Scheme of the HVopto regulation loop: the {\HVleftright}, coming from the HVPS, is modified by the opto-coupler (MOC8204) according to the DAC value, in order to have an {\HVout} value (going to the PMT) equal to the required one. This output value is monitored by the ADC at the right side of the scheme. |
 | Sketch of a partial super-drawer showing the external drawer (a) and the internal drawer (b). The two unconnected drawers are shown on the bottom. The HV components are indicated: the external HVbus board (1), the HVmicro board (2), the external HVopto board (3), the HVflex (4), the internal HVopto board (5) and the internal HVbus board (6). |
 | Comparison of the PMT gain variation measured by the Laser and computed using the monitored high voltage {\HVmeas} in the case of a channel with faults in the monitoring system. By definition, the first point is set to zero. |
 | Distributions of the values of the quadratic term of the polynomial function used for conversions of the DACs (left) and ADCs (right) of all the HVopto boards. |
 | Distribution of \mudhvi, defined in Section~\ref{subsec:unstable}, for all the stable channels of the EBA partition obtained analysing 2015 data. |
 | Comparison of the PMT gain variation measured by the Laser and computed using the monitored high voltage {\HVmeas} in the case of the stable channels PMT 15 of the module LBC08 (left) and PMT 46 of the module LBC08 (right). By definition, the first point is set to zero. |
 | Distributions of the values of the quadratic term of the polynomial function used for conversions of the DACs (left) and ADCs (right) of all the HVopto boards. |
 | Picture of the HVmicro board. The main components are: the micro-controller (1), the 256~KB flash memory (2), the 256~KB RAM (3), the 2~KB EEPROM (4), the two opto-couplers of the CANbus interface (5) and the connector for the CANbus cable (6). |
 | Drawing of a TileCal module showing the structure of the iron and scintillator tiles and the method of light collection by wavelength shifting fibres to the photomultipliers. The holes for the radioactive source tubes that traverse all the eleven radial tile-rows parallel to the colliding beams are also shown~\cite{tdr_tile,PERF-2007-01}. |
 | Comparison of the PMT gain variation measured by the Laser and computed using the monitored high voltage {\HVmeas} in the case of channels with faults in the regulation loop systems: PMT 43 of the module LBA20 (left) and PMT 26 of the module LBC51 (right). By definition, the first points are set to zero. |
 | Partial picture of the HVopto board showing four complete regulation loops. One of them is highlighted by the box (1). One opto-coupler (2), the two 100~M$\Omega$ HV resistors (3), the six 4-channels DACs highlighted by the box (4), the two $-5$~V regulators (5), the ADC (6), the voltage reference AD589 (7) and the 2~KB EEPROM (8) are also shown. |