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| d2:laser_controller [2019/08/29 17:20] – Michael Radunsky | d2:laser_controller [2020/05/04 19:02] – Michael Radunsky |
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| ====User Control of the Poles and Gain==== | ====User Control of the Poles and Gain==== |
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| If you remove the right side panel on the Laser Controller, for each stage of temperature control, you will see the panel shown in <imgref side_adjustb>. The set of click switches labeled "Integral" controls the PI (ω<sub>1</sub>) pole. Clicking the first switch, labeled "proportional," into the on position removes the integral gain (but not the differential gain). If the "proportional" switch is in the off position (integral gain is now on), then the sum of the times for all switches in the on position gives the RC time-constant for the PI pole. For example, if the 2<sup>nd</sup> (0.47s) switch and the 4<sup>th</sup> (2.2s) switch are in the on position (and the rest off), then the time constant is 2.7s and ω<sub>1</sub> = 1/2.7s = 0.37 Hz. | If you remove the right side panel on the Laser Controller, for each stage of temperature control, you will see the panel shown in <imgref side_adjustb>. The set of click switches labeled "Integral" controls the PI (ω<sub>1</sub>) pole. <color black/yellow>Clicking the first switch, labeled "proportional," into the on position removes the integral gain (but not the differential gain).</color> If the "proportional" switch is in the off position (integral gain is now on), then the sum of the times for all switches in the on position gives the RC time-constant for the PI pole. For example, if the 2<sup>nd</sup> (0.47s) switch and the 4<sup>th</sup> (2.2s) switch are in the on position (and the rest off), then the time constant is 2.7s and ω<sub>1</sub> = 1/2.7s = 0.37 Hz. |
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| Similarly, the switches labeled "Differential" control the D (ω<sub>2</sub>) pole. If the first switch, labeled "Diff On" is in the off position, then there is no differential pole. If the "Diff On" switch is on, then the D pole has an RC time-constant given by the sum of the times of all the switches in the on position, same as with the Integral bank of switches. | Similarly, the switches labeled "Differential" control the D (ω<sub>2</sub>) pole. If the first switch, labeled "Diff On" is in the off position, then there is no differential pole. If the "Diff On" switch is on, then the D pole has an RC time-constant given by the sum of the times of all the switches in the on position, same as with the Integral bank of switches. |
| - Turn on temperature loop. | - Turn on temperature loop. |
| - Adjust set-point to approximately desired temperature. | - Adjust set-point to approximately desired temperature. |
| - Turn up the gain. Keep increasing the gain until the temperature error (front panel BNC) just start to oscillate or ring with very little damping. If oscillation too large, reduce gain. Measure the period of oscillation. | - Turn up the gain. Keep increasing the gain until the temperature error (front panel BNC) just starts to oscillate or ring with very little damping. If oscillation too large, reduce gain. Measure the period of oscillation. |
| - Turn off the Laser Controller. Measure resistance between "GAIN" testpoint and "GND" testpoint. Turn down the "PROPGRAIN" until this resistance reads 1.7 times less than its original value (i.e. from 500Ω to 295Ω). | - Turn off the Laser Controller. Measure resistance between "GAIN" testpoint and "GND" testpoint. Turn down the "PROPGRAIN" until this resistance reads 1.7 times less than its original value (i.e. from 500Ω to 295Ω). |
| - Take the measured oscillation period in step 6 and divide by two. Set the Integrator time constant to this value. For instance, if you measured a period of oscillation of 14 seconds, turn on the 4<sup>th</sup> (2.2s) and 5<sup>th</sup> (4.7s) switches in the integrator bank, to get a time constant of 6.9s. | - Take the measured oscillation period in step 6 and divide by two. Set the Integrator time constant to this value. For instance, if you measured a period of oscillation of 14 seconds, turn on the 4<sup>th</sup> (2.2s) and 5<sup>th</sup> (4.7s) switches in the integrator bank, to get a time constant of 6.9s. |
