1 | function [Tau, I0, t, DCCT, chi2n] = measlifetime(varargin) |
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2 | %MEASLIFETIME - Measures the lifetime using an exponential or linear least squares fit to beam current |
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3 | % [Tau, I0, t, DCCT] = measlifetime(t, DCCT) |
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4 | % [Tau, I0, t, DCCT] = measlifetime(t) |
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5 | % [Tau, I0, t, DCCT] = measlifetime |
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6 | % |
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7 | % INPUTS #1 - t is a vector or positive scalar |
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8 | % 1. t = a. If vector, time [seconds] (vector input) |
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9 | % b. If scalar and t > 0, length of time in seconds to measure current |
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10 | % Default sample period is .5 seconds. |
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11 | % 2. DCCT = current vector [mAmps] |
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12 | % if the DCCT vector is empty then this function will |
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13 | % get the current using getdcct at the times defined in t |
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14 | % 3. Method - 'Exponential' for exponential least square fit |
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15 | % - 'Linear' for linear least square fit |
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16 | % |
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17 | % or |
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18 | % |
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19 | % [Tau, I0, t, DCCT] = measlifetime(DCCT_Drop, Tmax, Tmin, Nmin) |
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20 | % |
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21 | % INPUTS #2 - "t" is negative |
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22 | % 1. DCCT_Drop - If DCCT_Drop is scalar and DCCT_Drop <= 0, then the beam current will be |
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23 | % monitored until the current is DCCT_Drop. Default sample period is .5 seconds. |
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24 | % Default: Monitor the beam current until current drops 60 uA |
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25 | % (At Spear sigma(DCCT) = 0.001 mA) |
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26 | % 2. Tmax - Maximum time to measure DCCT {Default: inf} |
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27 | % 3. Tmin - Minimum time to measure DCCT {Default: 0} |
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28 | % 4. Nmin - Minimum number of unique data points when monitoring DCCT drop {Default: 6} |
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29 | % |
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30 | % The goal is to measure the current until a current drop of DCCT_Drop is achived. However, the |
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31 | % time that takes will never goes above Tmax. And if DCCT_Drop is achived then the measurement will |
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32 | % continue until Tmin or Nmin points is achieved (but not exceeding Tmax). |
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33 | % |
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34 | % |
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35 | % OUTPUTS |
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36 | % DCCTfit = I0 * exp(-t/Tau); Exponential |
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37 | % DCCTfit = I0 * (1-t/Tau); Linear |
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38 | % 1. Tau - Computed lifetime [hours] |
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39 | % 2. I0 - Computed [mAmps] |
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40 | % 3. DCCT - Beam current vector [mAmps] |
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41 | % 4. t - Actual time [Seconds] |
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42 | % 5. chi2n - normalized chi2 |
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43 | % |
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44 | % |
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45 | % NOTES |
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46 | % 1. If no output exists, the beam current and fit will be plotted to the screen |
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47 | % as well as the residual of the DCCT. |
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48 | % 2. DCCT is assumed to be in mAmps |
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49 | |
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50 | % |
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51 | % Written by Gregory S. Portmann |
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52 | % Modified by Amor Nadji, May 2005 |
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53 | % Adapted by Laurent S. Nadolski, 23/01/06 |
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54 | % Added covariance calculation |
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55 | |
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56 | % Default method if not user given |
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57 | MethodFlag = 'Exponential'; |
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58 | sigma = 0.2e-6; % Error in dcct measure in Amps for 7 read per second config |
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59 | |
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60 | % Parser for method |
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61 | for i = length(varargin):-1:1 |
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62 | if strcmpi(varargin{i},'Linear') |
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63 | MethodFlag = 'Linear'; |
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64 | varargin(i) = []; |
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65 | elseif strcmpi(varargin{i},'Exponential') |
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66 | MethodFlag = 'Exponential'; |
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67 | varargin(i) = []; |
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68 | end |
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69 | end |
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70 | |
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71 | T_Seconds = .5; % Default sample period [Seconds] |
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72 | TmaxDefault = inf; % Maximum time |
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73 | TminDefault = 0; % Minimum time |
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74 | NminDefault = 6; % Minimum number of data points |
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75 | |
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76 | |
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77 | % Input parsing |
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78 | Tmax = []; |
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79 | if length(varargin) == 0 |
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80 | MonitorFlag = 2; |
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81 | deltaDCCT = 60 * 0.001; |
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82 | Tmin = TminDefault; |
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83 | Tmax = TmaxDefault; |
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84 | Nmin = NminDefault; |
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85 | |
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86 | elseif length(varargin) >= 1 |
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87 | t = varargin{1}; |
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88 | if all(size(t)==[1 1]) |
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89 | if t > 0 |
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90 | MonitorFlag = 1; |
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91 | t = 0:T_Seconds:t; |
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92 | Tmax = TmaxDefault; |
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93 | else |
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94 | MonitorFlag = 2; |
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95 | deltaDCCT = abs(t); |
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96 | if length(varargin) >= 2 |
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97 | Tmax = DCCT; |
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98 | else |
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99 | Tmax = []; |
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100 | end |
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101 | end |
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102 | if length(varargin) < 3 |
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103 | Tmin = []; |
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104 | end |
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105 | if length(varargin) < 4 |
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106 | Nmin = []; |
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107 | end |
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108 | if isempty(Tmax) |
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109 | Tmax = TmaxDefault; |
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110 | end |
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111 | if isempty(Tmin) |
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112 | Tmin = TminDefault; |
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113 | end |
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114 | if isempty(Nmin) |
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115 | Nmin = NminDefault; |
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116 | end |
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117 | else |
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118 | % Time vector input |
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119 | if length(varargin) < 2 |
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120 | MonitorFlag = 1; |
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121 | else |
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122 | MonitorFlag = 0; |
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123 | end |
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124 | end |
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125 | end |
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126 | |
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127 | |
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128 | if MonitorFlag == 1 |
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129 | |
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130 | % Get DCCT data at a fix interval determined by the input vector t |
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131 | %disp([' Monitoring beam current for ', num2str(t(length(t))), ' seconds.']); |
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132 | t0 = gettime; |
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133 | for j = 1:length(t) |
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134 | T = t(j) - (gettime-t0); |
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135 | if T > 0 |
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136 | pause(T); |
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137 | end |
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138 | tout(j,1) = gettime - t0; |
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139 | DCCT(j,1) = getdcct; |
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140 | end |
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141 | |
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142 | elseif MonitorFlag == 2 |
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143 | |
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144 | % Monitor for a fixed DCCT drop |
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145 | %disp([' Monitoring beam current until current drops by more than ', num2str(deltaDCCT), ' mA.']); |
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146 | j = 1; |
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147 | n = 1; |
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148 | tout(n,1) = 0; |
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149 | DCCT(n,1) = getdcct; |
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150 | t0 = gettime; |
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151 | t0_Display = 0; |
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152 | while ((abs(DCCT(end,1)-DCCT(1,1)) < deltaDCCT) & (DCCT(end,1) > 0.1)) | ... |
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153 | n < Nmin | (gettime-t0) < Tmin |
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154 | j = j+1; |
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155 | T = (j-1)*T_Seconds - (gettime-t0); |
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156 | if T > 0 |
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157 | pause(T); |
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158 | end |
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159 | DCCTnew = getdcct; |
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160 | if DCCTnew ~= DCCT(n) |
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161 | n = n + 1; |
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162 | tout(n,1) = gettime - t0; |
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163 | DCCT(n,1) = DCCTnew; |
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164 | end |
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165 | if gettime-t0 > Tmax |
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166 | break; |
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167 | end |
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168 | if gettime-t0_Display > 10 |
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169 | fprintf(' Monitoring DCCT for lifetime measurement (%s)\n', ... |
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170 | datestr(clock,0)); |
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171 | t0_Display = gettime; |
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172 | end |
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173 | end |
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174 | t = tout; |
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175 | end |
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176 | |
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177 | % Column vectors |
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178 | DCCT = DCCT(:); |
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179 | t = t(:); |
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180 | |
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181 | |
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182 | % Lookfor identical data in DCCT. Some machine don't update at T_Sample and |
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183 | % having the same reading twice is probably not so good for the LS fit. |
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184 | iExtra = find(diff(DCCT)==0); |
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185 | DCCT(iExtra) = []; |
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186 | t(iExtra) = []; |
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187 | |
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188 | if length(DCCT) < 2 |
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189 | Tau = NaN; |
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190 | I0 = NaN; |
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191 | fprintf(' Only 1 unique DCCT reading, hence Tau is set to NaN.\n'); |
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192 | %error('There must be at least 2 unique point to fit a lifetime.'); |
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193 | return |
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194 | end |
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195 | |
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196 | |
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197 | % LS fit |
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198 | if strcmpi(MethodFlag,'Exponential') |
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199 | y = log(DCCT); |
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200 | else |
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201 | y = DCCT; |
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202 | end |
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203 | |
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204 | X = [ones(size(t)) t]; |
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205 | |
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206 | % Linear Least square fit |
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207 | invXX = inv(X'*X); |
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208 | B = invXX*X'*y ; |
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209 | |
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210 | if strcmpi(MethodFlag,'Exponential') |
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211 | % yfit = exp(B(1))*exp(B(2)*tfit); |
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212 | I0 = exp(B(1)); |
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213 | Tau = -1/B(2)/3600; % In hours |
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214 | yfit = exp(B(1))*exp(B(2)*t); |
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215 | stitle = 'Least Squares Fit : I0*exp(-t/tau)'; |
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216 | else |
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217 | % yfit = B(1) + B(2)*tfit; |
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218 | I0 = B(1) ; |
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219 | Tau = -B(1)/B(2)/60/60; % In hours |
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220 | yfit = B(1) + B(2)*t; |
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221 | stitle = 'Least Squares Fit : I0*(1 - t/tau)'; |
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222 | end |
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223 | |
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224 | %% Erreur |
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225 | %chi2 = 1/(sigma*sigma)*sum(power(DCCT - yfit,2)); |
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226 | chi2 = 1/(sigma*sigma)*sum(power(y - B(1)-B(2)*t,2)); |
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227 | % Normalized chi2 |
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228 | chi2n = chi2/(length(t)-length(B)); |
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229 | % Covariance matrix |
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230 | Mcovariance = chi2n*invXX; |
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231 | |
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232 | if strcmpi(MethodFlag,'Exponential') |
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233 | dtau = sqrt(Mcovariance(2,2)/B(2)/B(2))/3600; |
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234 | else |
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235 | dtau = sqrt(Mcovariance(1,1)/B(2)/B(2) + ... |
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236 | power(B(1)/B(2)/B(2),2)*Mcovariance(2,2) - ... |
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237 | 2*B(1)/power(B(2),3)*Mcovariance(2,1)); |
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238 | end |
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239 | |
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240 | if isnan(Tau) || chi2n > 5 |
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241 | fprintf(' Life time measurement is inaccurate!\n'); |
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242 | end |
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243 | |
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244 | if nargout == 0 |
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245 | |
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246 | clf reset |
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247 | subplot(2,1,1) |
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248 | plot(t,DCCT,'o-b', t,yfit,'--r'); hold on; |
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249 | % errorbar(t,DCCT,sigma*ones(size(DCCT)),'.b'); hold off |
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250 | title(sprintf('Beam Current vs Time: Lifetime= %2.2f +/- %2.2f (h) with chi2n = %2.2g', Tau, dtau, chi2n)) |
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251 | % title(sprintf('Beam Current vs Time: Lifetime= %2.2f (h) with chi2n = %2.2g', Tau, chi2n)) |
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252 | xlabel('Time [seconds]'); |
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253 | ylabel('Beam Current [mA]'); |
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254 | legend('Measured Beam Current',stitle,0); |
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255 | grid on; |
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256 | xlim([t(1) t(end)]); |
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257 | |
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258 | subplot(2,1,2) |
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259 | plot(t,DCCT-yfit); |
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260 | title(['Residual Error (RMS = ' num2str(std(DCCT-yfit),'%.2g') ' mA)']); |
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261 | xlabel('Time [seconds]'); |
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262 | ylabel('Lifetime Corrected Beam Current Variation'); |
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263 | grid on; |
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264 | |
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265 | addlabel(1,0, datestr(clock,0)); |
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266 | end |
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