Workshop JRA1- INFN Legnaro, 19/2005 A LabView® software for Automatized Electropolishing

Aim of work The minimum of derivative dI/dV of I-V characteristic curve is the best point of EP. The aim of work is obtaining the best EP of Niobium and Copper seeking and following the working point automatically.

Tuning of the EP process in the minimum of the differential conductivity dI/dV Typical I-V polarization curve for EP The best polishing is obtained by keeping the voltage always in the plateau. But the polarization curve is not fixed and moves dynamically The method consists in computer monitoring the I-V characteristic. The numeric derivative of I versus V is automatically displayed and the working point is chosen as the minimum of the bath differential conductance dI/dV that corresponds to the point of maximum resistance of the viscous layer.

Scheme of the automated EP Analogical signals Electrolytic cell Voltage Supply PLC PC Automation Software Digital Input-output VOLTAGE CONTROL REGIME The best working point of the I-V characteristic is searched and followed by during the whole EP process

The apparatus The apparatus is made of : Industrial power supply, controlled by analog current signal. Special PLC, the FieldPoint® FP-2010 by National Instruments, that uses the software written by LabView® 7.1. Test electrolitic cell The LabView® program is written on a computer, and then transferred on the memory of FieldPoint®.

Remote control The Hardware consists in a ALINTEL S4000 power supply (100Vmax - 40V max) with remote controller 0-10 V applied to the pins at the interface produce 0-100 V in output The analog readings from the Power supply are converted to digital in a PLC and elaborated by the automation software The digital output from the automation software are converted in voltage signals that drive the Power supply Remote interface

Input/Output Channels PLC The PLC is a LabView® programmable National Instruments Field Point 2010 It is composed by: 2 modules 1 supply 1 RS-232 Serial interface 1 Ethernet 10/100 Mbps It is possible to drive the process by several PC’s connected to the PLC in a network ETHERNET o RS-232 ports Input/Output Channels

Set up and preliminary tests of the automated procedure for Cu EP It has been built a test electrolytic cell with variable cathode area The Cu electrodes can be easily substituted by Nb electrodes, once that the “Automated EP programme” has been definetely set up

The program The control software of electropolishing is written in LabView 7.1, that is a graphical language specifically designed for interface and control the instruments of National Instruments. This language meets a simple graphic interface and a powerful set of function. The core of program is the algorithm for search and pick the working point.

Initial scan Initial scan parameters Calculated numerical derivative minimum The program initially makes a large scan from two values set by user. After the scan, the software calculates the derivative of the I-V curve, and sets the voltage that match to minimum point.

Following the minimum The program mantains the voltage for a time value set by user, after it makes a little scan around the minimum voltage. By recalculating the derivative, the program follows the new voltage minimum.

Rescanning the characteristic curve After a time set by user, the program uses the initial data to rescan the characteristic curve. This system allows to the program to adjust the minimum if the working point goes away from plateau

Automatic and semi-automatic function New manual minimum Confirm the manual minimum If the point found by program isn’t at right place, the user can stop the automatic search and manually sets a new minimum. The program continue the automatic search on the new minimum.

Niobium The program was tested on Niobium, but the electrolitic cell wasn’t cooled properly, so the I-V curve displays oscillations. Oscillation create difficulties on setting the working point.

The Movie

Conclusion The automatized program for EP is succesfully applied to Copper. Work on Nb requires more attention and it is on progress The program can auto-correct the errors of working point by rescanning the I-Vcurve. The semi-automatic function allows to study another points on characteristic curve. All parameters can be changed in real time.