PS Transverse Feedback Pick-up Amplifier

Gain control

The PU gain can be controlled by an application program accessible in the 'Tests' menu of the CPS Console Manager. This is really a specialist's tool, and does not protect you from making erroneous settings.

To set gains, first select a USER line from the PLS menu. The sliders move automatically to the presently active values. The sliders cover a range of 40dB. The value shown next to the sliding cursors is what is actually written into the hardware gain registers (see: Remote Control) of the pre-amplfier hardware for the USER line shown at the top of the window.

The rules to appropriately set the gain are as follows:

1. Select the attenuator setting according to the approximate beam intensity:
   •   0dB below 6e10 ppb
   • 20dB between 6e10 and 6e11 ppb
   • 40dB between 6e11 and 6e12 ppb
   • 60dB above 6e12 ppb
2. Adjust the Sum slider to obtain a reasonable output level (1..2 Vp) for the Σ channel.
3. Adjust the X and Y sliders to obtain the desired displacement sensitivities. The slider should normally end up between values 64 and 132. If you have to set them higher, then a lower attenuation will probably yield a better S/N ratio. It you have to set them lower, you risk signal distortion due to the saturation of intermediate gain stages. This may not be clearly evident from a scope observation of the signals!

The transfer parameters are calculated from the gain and attenuator settings, and from the known properties of the PU electrodes. Until I have had time to verify this by actual measurement, you should not take these parameters too seriously.

The buttons in the 'Test relays' frame control the relays via which test signals can be applied to the PU electrodes. At most one should be set at a time. The setting is common to all USER lines, to avoid wearing out the relays by switching them too often. Test signals can be applied via the 'Test' cable in the damper room. (See the cabling diagram for SS02 and for SS98.) The transfer ratio, applied voltage over electrode voltage, is ??dB and the simulated position is (???,???) mm.

The gain control program executable for Linux is also available from /afs/cern.ch/user/j/jeroen/public/tfpu. The program has no command line parameters and does not need any of the standard PS environment variables. It does require a certain number of shared libraries, however. Give me a call if that appears to be a problem.