PS wirescanner calibration

PS wirescanner calibration

Student Meeting10/03/2014

Carolina Bianchini

BE-BI-BL

10/03/2014 Carolina Bianchini 2

Outline

Wirescanner calibration

Calibration analysis

Conclusions

Calibration analysis...new method

10/03/2014 Carolina Bianchini

Wirescanner calibrationWire Scanners are devices used for beam-profile measurement in the LHC and its injectors.

3


Wire Scanners calibration is needed to correlate the potentiometer values with the projected position of the beam.

Wirescanner calibrationPS Wirescanner



Laser Splitter Photodiode

Combiner

Wirescanner

PS Wirescanner calibration bench


PS Wirescanner calibration procedure1. We move the system along the vertical axis with fix step and

we record, at each position, the profile of the laser-beam. We repeat these measurement at two different speed: 10m/s and 15m/s.


Bits (angular position)

Phot

odio

de s

igna

l




Phot

odio

de s

igna

lPS Wirescanner calibration procedure1. At each position, we have to find the center of the two peak

(in potentiometer bit).


PS Wirescanner calibration procedureFor each scanned position we plot the potentiometer center of

the laser beams as function of the position.We fitted it with a polynomial curve.

3.



PS Wirescanner calibration procedureThe best polynomial curve order is chosen minimizing the

average difference between the fit and the real values and looking for the best average of the peaks distance.

4.

We generate a table to correlate the motor angular position (in bit) vs the projected position (in mm).



• Actually the calibration data analysis is performed using a Java application written by BE/BI/SW.

• The calibration data analysis is carried out in 3 steps:– Identification of the signals

obtained during the measurements;

– Identification of the two laser peaks. The first peak is the absolute minimum value of the signal registered by the photodiode. The second peak is found as the second minimum value in the

region lowered by at least 40% of the previous peak value.

- Generation of the tables. 10

Calibration analysis


Calibration analysis The method developed by Emiliano follows these steps: 1. Laser signal is cut with fix threshold (|Max-Min|*40%).2. Average values in the first and in the second couple of

points where the threshold is equal to the signal are calculated (P1 and P2).

3. Plot the average between P1 and P2 vs the projected position.

4. Fit the previous curve with polynomial function.5. Generate calibration table.

11


Calibration analysis...new methodMy expected work as technical student is to develop a program

with new mathematical routines and fit functions which will standardize calibrations quality assurance.During my first 3 months I have developed an alternative method in MATLAB to better perform the calibration data fit.I follow these logical steps:1. I load data file to MatLab;2. I take the signal and I divide into IN and OUT profile;

12


3. I apply a threshold in order to clean the signal by the noise and I smooth the signal;

13



4. I find 4 points where the signal is equal to the threshold (A, B, C, D).

14

A B C D



5. I divide the signal into 2 different regions, A-B and C-D.6. In each region I apply another smooth (lower order) and I

use a Gaussian fit to calculate the center of the peak. I obtain 2 values, peak1 and peak2.

15



8. I calculate the average peak1, peak2 and I plot it vs position (in mm).

16



9. I fit this curve with different polynomial order function and I choose the best polynomial result to generate the calibration table.

17



15m/s IN

improvement

Posi

tion

diffe

renc

e (m

m)

Average absolute error107µm


0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

29000 29500 30000 30500 31000 31500 32000 32500 33000 33500 34000

C1-C2

C1-C3

C2-C3





WS PS 146382 OLD METHOD (µm) EP METHOD (µm) NEW METHOD (µm)

10 m/s IN 105 85 78

15m/s IN 195 100 95

10 m/s OUT 116 85 79

15m/s OUT 107 75 71



Conclusions• New routines seems to improve PS & PSB calibration

reliability.• First attempt done in MatLab showed good results, taking

into account the electronic noise in the potentiometer reading.

• Different filters are still under studying.• Once the procedure will be tested on all the PS & PSB

calibrations, a final software will be developed in Python.

20


Emiliano

Thanks to...

Documents

PS wirescanner calibration