a. Power supply test†††††††††††††††††††††††††††††††††††††††††††††††††† Jeter Hall
2. DAQ specs †††††††††††††††††††††††††††††††††††††††††††††††††††††† Jeter Hall
1) We discussed the DCRC V2 schematic:
The bipolar LED drive, with the polarity
remotely selectable on the fly, can be implemented if it will really be needed
and used, but otherwise we should avoid the extra complication it adds to the board.
Our plan for now is to use a jumper to select the polarity, which is fine for
tests to choose the best one, but not if you know we're going to want to flash
routinely with each LED. We can also revisit this for DCRC V3.
Update from DTC meeting:† We agreed that one jumper to switch both polarities is sufficient. †We have agreed to supply a test-point to allow the LED voltage to be measured. †We discussed providing an on-board voltage measurement, but it didnít pass our cost-benefit judgment.
The QET bias DAC will be set up as we have now,
with a +-2mA range, and a jumper to select +-4 mA range, and 12 bits of
adjustment. This DAC can also be used to program an Ibis
measurement. In addition, a signal generator chip will provide sine wave
and other small signals on top of the QET bias. A frequency sweep is also
available. The amplitude of the small signal is selectable with 10 bits
of adjustment. We'll set the maximum amplitude at 100 micro-amps.
Thus, the minimum amplitude won't be all the way down in the noise, but about
10 nano-amps in the QET. If you want to go smaller than this, we'll have
to reduce the maximum amplitude.
Update from DTC meeting:† We agreed that a jumper to select the QET bias range is sufficient, though Sten will probably use an on-line-addressable switch since itís almost as easy.
We chose a maximum amplitude for the signal generator of 10 micro-amps to allow for very small test signals.
∑ Sten will follow a suggestion to simplify the test signal input in a way that also avoids extra noise from two resistors (possible because itís a low-impedance current summing node).
∑ An AD600 chip provides variable feedback gain from 1 to 100, and is made to match the AD797 pre-amp.
∑ The new feedback amp also puts the signal inversion the same as the old system.
∑ Jeter tested new power supplies for DCRC V2 and found that they reduce the power in the noise spikes and also move those spikes up in frequency and so farther from our signal region.
2) Jeter discussed his compilation of DAQ specs.† There was a suggestion that this should get an even wider hearing at a collaboration meeting.† We also discussed using a run database for saving all parameters used in data-taking, flashing, etc.