Transcript transparencies

Calorimeter Cell description in PVSS data base (Proposal)
• Introduction
Which HV to be set before beam will come?
Needed Constants
• PVSS data point type (DPT) format of HV channel
• DCS system architecture
LHCb meeting 29.11.05
Anatoli Konoplyannikov
1
Calorimeter Cell description in PVSS data base (Proposal)
A calorimeter HV setting will be needed in time of detectors commissioning and normal
operation. Mainly the correct HV and timing settings will define a calorimeter trigger
performance. Procedure of the HV setting must be simple for users and flexible for various
gains. The HV setting will be done through the LHCb ECS system and it is important to define
the calorimeter cell description into a PVSS data base in a way that allows to satisfy desired
goals. There are few possibilities of this description e.g. using traditional method with an
individual HV set and voltage - current monitoring (like the CAEN HV system Framework) or
one can make a dedicated description takes into account the specific characteristics of the
calorimeter HV hardware (based on CW converters and HV_LED_DAC control signal
distribution boards).
A proposed idea is to prepare description of each calorimeter cell in the way that allows to set
only one parameter per detector and all the rest settings will be done automatically. The
parameter is a needed mean PMT gain. In other words I propose to describe a calorimeter
cell HV setting value by a formula with only one variable and few constants.
DACcode(i) = f(GAINmean, C1(i),...CN(i)), where DACcode(i) – individual 12 bit DAC code
writing by ECS; C1(i),...CN(i) – set of the individual per cell constants.
Some constants can be calculated and others must be measured during commissioning time
and later with beam in the calibration runs.
Below I will try to define these constants and explain a possible way of measurement.
LHCb meeting 29.11.05
Anatoli Konoplyannikov
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Calorimeter Cell description in PVSS data base (Proposal)
It was decided that the PMT responses of the LHCb calorimeters will follow the Pt distribution.
The formula below shows relation between a PMT response on one GeV particle energy loss and
a calorimeter mean gain.
PMT response for a calibrated calorimeter cell.
RESPpmt(i) = Cfe(i)*Qpmt(i) = Cfe(i)* Coptics(i)* Cpt(i)*GAINmean, [ FE ADCcnt / GeV ]
where: Qpmt is a collected charge;
Cfe - front end analog circuitry (fast integrator, ADC) transfer coefficient;
Cpt – a Pt distribution constant calculated for each cell follow the Pt distribution,
Coptics – a complex constant (could be partially calculated) related to a detector cell
optics quality, light collection efficiency, a PMT photo cathode quantum efficiency and so on. In
the beginning of a detector commissioning a default value could be calculated with using data
obtained from a radioactive source calibration of HCAL and a cosmic pre-calibration of ECAL.
Then a beam calibration will be needed for a more precise definition of this constant.
GAINmean – a required mean value of the detector PMT gains, or a gain for a defined
reference cell.
The individual PMT gain is defined by formula: GAINpmt(i) = Cpt(i)*GAINmean.
Let define the cell response constant as: Cresponce = RESPpmt(i) / GAINmean*Cpt(i). This
constant must be the same for all calorimeter cells of a good calibrated detector.
Finally the formula looks like: GAINpmt(i) = Cresponce / Coptics(i).
The aim of the HV system is set the needed control values for obtaining required GAINpmt
satisfying the previous formula.
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
Now a few formulas show relations between phototube gain and DAC codes.
PMT gain and high voltage relation.
Gain versus high voltage V dependence is well defined by a function
GAINpmt(i) = A(i)*VB(i)
for the used Hamamatsu PMTs it is correct for a gain more than 10 000 and we have the A an B
constant values from Hamamatsu data sheet and the test bench measurements. For obtaining
the correct function for a lower gain an additional measurement with LED monitoring system will
be needed (commissioning time). A new formula GAINpmt = f(V) can be more complicated and
includes more constant parameters.
PMT high voltage and control voltage relation.
The control voltage produced by DAC IC feeds a CW voltage converter of the PMT base. The
dependence of HV versus an applied DAC CODE looks like:
V = Cdac(i)*Ccw(i)*DACcode,
where Cdac – a DAC transfer function coefficient;
Ccw – a CW base voltage converter multiplication factor.
The distribution of the Cdac coefficients has been measured for three pre-series HV_LED_DAC
control boards and for one is shown below. The distribution of the Ccw coefficients was shown
some times ago on a calorimeter meeting.
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
Cathod voltage distribution for
first sample of 50 bases
Cdac = DACout(V) / DACcode(cnt)
DAC ICs transfer coefficients distribution for 200
channels of HV_LED_DAC board RMS ~ 0.3 %
Spread of Uc: (Uc(max)-Uc(min))/Uc(mean) ~1%
Uset=4.8v
~1% of HV spread --- ~10% GAINpmt(i) spread  Cdac(i) and Ccw(i) must be measured
PMT response and FE ADC output relation
Each front end analog circuitry (fast integrator, ADC) has an individual transfer coefficient. The
formula looks like:
RESPpmt = Cfe(i)*Qpmt [ ADC counts ].
The Cfe coefficients could be obtained during a FE boards postproduction calibration.
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
Finally the formula for calculation of a DAC input code (12 bits ) looks like:
DACcode(i) = exp( ( log( (1/Cfe(i))*Coptics(i)*Cpt(i)*GAINmean) - Ac(i) ) / Bc(i) )
One looking on the formula can define:
• the commissioning tasks for the correct procedure of the calorimeter HV
settings (calculation and measurement needed constants);
• the input values for a calorimeter data base.
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
PART I Conclusion
Summary of constants describing an individual cell
Defined and calculated
• Cpt – constant of the PMT response follow by needed Pt distribution
• A, B – parameters of the function of a PMT gain versus HV dependence (gain > 10000).
Measured in commissioning time
• A, B, C ... – parameters of the function of a PMT gain versus HV dependence (gain <
10000)
• Cdac – parameter of a DAC IC transfer function
• Ccw - CW base voltage converter multiplication factor
• Cfe – parameter of a FE integrator and ADC transfer function
• Coptics – constant of detector cell quality and optic attenuation
Unfortunately, as one can see, the many constants not so easy to measure or re-measure (e. g.
Cdac, Ccw, A, B). In the same time we can define one combined constant from the mentioned
above and responsible for a PMT gain and make a gain calibration (with LED system) for all
calorimeter cells equipped with the final PMTs, CW bases and DAC channels. After this calibration
we will get the function GAINpmt(i) = f( DACcode(i) ), that includes all hardware constants and
then calculate parameters Ac(i), Bc(i) ...
LHCb meeting 29.11.05
Anatoli Konoplyannikov
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Calorimeter Cell description in PVSS data base (Proposal)
Possible implementation of the calorimeter cell description in
LHCb PVSS ECS system
An additional information describing hardware addresses, useful info and reading
values will be needed for complete a HV channel definition in the ECS data base.
Additional constants of a calorimeter cell describe a geometrical position, the
hardware boards addresses and monitoring values:
• geometrical position (HO0101L);
• PMT or CW base name (LA5080);
Channel Info
• FE board address (220204);
• HV board address (3);
• Channel (1);
• Control voltage readings (1500);
• 100 V power supply protection circuit status (ON/OFF);
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
HV Channel
info
settings
description
board
channel
constants
Cpt
Ac
Bc
readings
g0set
v0
switchOn
isOn
rampUp
rampDown
unsigned int
float
bool
Cfe
string
Coptics
dpid
limits
vMin
vMax
Data Point Type definition of the CALO HV channel
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
Supervisory Application
User
Framework
PVSS
Device Editor
Navigator
Controls
Hierarchy
Data
Manager
Event
Manager
Devices
DIM
Custom FE
CALO_HV DIM Server
System Architecture for HV control
HV control boards
LHCb meeting 29.11.05
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Calorimeter Cell description in PVSS data base (Proposal)
Conclusion
The possible way of a calorimeter cell definition in sense of HV setting is proposed.
The needed constants those to be defined and measured were described.
The PVSS Data Point Type description of a calorimeter cell and a DCS system
architecture was presented too.
LHCb meeting 29.11.05
Anatoli Konoplyannikov 11
Calorimeter Cell description in PVSS data base (Proposal)
Appendix
HV control signal board overview.
200 channel control boards with DAC ICs produce the control voltages for CW bases.
All boards are connected to ECS with using the SPECS bus.
On each board there is possibility to read back the individual control voltage values, status of
the eight over current (100 V) protection chains and low voltage power supplies values.
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