Date post: | 04-Jan-2016 |
Category: |
Documents |
Upload: | lenard-bryant |
View: | 213 times |
Download: | 0 times |
Design of a readout system Design of a readout system for RPCsfor RPCs
Olu Amoda 2
The LODEN GroupThe LODEN Group
The group is an association of Fermilab scientists who teamed up to build a cosmic ray detector from RPCs.
I was assigned as intern to this group and I helped in building a readout for RPCs
Olu Amoda 3
Resistive Plate Resistive Plate Chamber(RPC)Chamber(RPC)
An RPC is a glass chamber filled with a mixture of gases,an electric field supplied by an High Voltage source. It is used to detect charged particles through their interactions with the molecules of the gases.
The particles strip off electrons from the molecules of the gases, which results in a spark inside the chamber.
The spark induces a voltage on an adjoining readout system.
Olu Amoda 4
SchematicsSchematics
Olu Amoda 5
How it worksHow it works
Glass electrodes are used to apply an electric field of ~4kV/mm across a 2mm gap.The gap has a mixture of argon,isobutane and HFC123a gas. An ionizing particle initiates a discharge which capacitively induces a signal on external pickup strips.
Olu Amoda 6
Building a Readout SystemBuilding a Readout System
Factors taken into consideration:CostEfficiency AvailabilityConstruction.
Olu Amoda 7
Inductive Readout SystemInductive Readout System
Is a capacitor like setupWith two surfaces, one for signal
transmission and the other for signal protection.
A dielectric material between the surfaces
Olu Amoda 8
Two Methods of ConstructionTwo Methods of Construction
Strip readout Method: A board is stripped
vertically and another one horizontally.
A signal is picked by a a vertical and horizontal strip
Both strips locates position.
Padded r/out Method: Board is partitioned
into square segments. A signal is picked up a
square segment Square segment
locates position
Olu Amoda 9
Diagram of Readout SystemsDiagram of Readout Systems
Strip Readout System Padded Readout System
Olu Amoda 10
The strips method was chosen over the padded method due to the following reasons. 1) It is easier to make strips on a board than to make square segments. 2) For a large area of RPC it will cost much more to attach signal cable to each square than to each strip. 3) For a a board of dimension a by b, we need a*b for square segments, while we need a+b for strips.
Strips over PadsStrips over Pads
Olu Amoda 11
Material for constructionMaterial for construction
Copper strips on mylar foil is normally used for a strip readout board.
Copper and mylar are every expensive.An home insulating board from home depot
was used as a substitute for the “copper strips on mylar”.
Olu Amoda 12
The BoardThe Board
As one side made of aluminum.
Another side made of aluminum coated with insulating material.
A dielectric made of foam.
Olu Amoda 13
What next ?What next ?
Make strips of different width on the board.Setup experiment to:
– Study signal transmission in each strip.– Determine the right strip for experiment– Study reflection.
Olu Amoda 14
Pre-ExperimentPre-Experiment
Strips were made on the board by a saw.
The ends of the ground plane were cleaned with ethyl , for cable attachments.
Olu Amoda 15
Purpose of Experiment:Purpose of Experiment:To DetermineTo Determine
The width of the strip that will give the least backend reflection
The terminating impedance at the back of the board for each strip
The strip that gives the least front end reflection, after termination .
Olu Amoda 16
Experimental SetupExperimental Setup
Olu Amoda 17
Reflections in CablesReflections in CablesWhen signals travel trough two cables of
different impedances, reflections are setup at the boundary of the two cables.
If two cables of impedances R and Z are connected to each other, ρ gives the value of reflection for both cables.
ZR
ZR
R Z
Olu Amoda 18
ProblemProblem
A pulser was required to generate pulses.A pulser output feeds a 50 ohm coaxial
cable.120 ohm twisted-flat cable was to receive
pulses from the pulser.Problem: Interconnecting the two cables
directly will pose a problem.Why?
Olu Amoda 19
Avoiding ReflectionsAvoiding Reflections
When two cables of different impedances are to be connected to each other.
The principle of termination is employed.Termination is the addition of
supplementary impedance(s) to the impedances of two cables.
Termination can be done either in series or in parallel or a combination of both.
Olu Amoda 20
ApplicationApplication
The circuit represented by the circuit diagram was designed to connect the 120 ohms and 50 ohms cable.
It helped to avoid reflections at the interface of the two cables.
Olu Amoda 21
ProceduresProcedures The diagram shows a typical
display on the oscilloscope Termination was done on a
trial and error basis. Resistors attached in turn, to
flatten out backend The values and displays were
recorded for further analysis.
Olu Amoda 22
ResultsResultsDimension of board: 2m x 0.9m x1.25m
Olu Amoda 23
Analysis of ResultsAnalysis of Results
The result was tested for experimental accuracy by comparing with a theoretical equation.
The resistors vs width/thickness ratio was plotted on the same graph with the theoretical equation
Impedance Equation
Olu Amoda 24
ComparisonComparison
The values obtained from the experiment are accurate to a certain degree.
The experimental values were well distributed around the equation line.
Olu Amoda 25
Conclusions from experiment.Conclusions from experiment.
All strips widths are okay for further experimental purposes
Strip of width 1.8 cm gave the least front-end reflection
Reflections at the front end are negligible. Strip of width 3cm was selected for further
experimental purposes