We measured discharges in the SWAMPs by unplugging the OMs and feeding the pick-ups with nominal high voltage. The channels were investigated one by one by connecting the prompt output to an oscilloscope. Simultaneously prompt outputs from two other channels in different crates were connected to the oscilloscope in order to tell global and local signals apart.
We observed two main types of signals. Type A consists of well defined spikes restricted to one channel. These events are most likely caused by discharges in the pick-up boxes. Types B1 and B2 are global electronic noise which was seen in the investigated channel as well as the two reference channels, independent of where the latter two were connected. Signals of type B1 correspond to a peak amplitude less than 150 mV, whereas all signals with higher peak amplitude are denoted B2.
Measurements were performed during two minutes for each channel with a SWAMP card, regardless of wether the SWAMP was connected to the DAQ or not. First the offset and noise level were measured with roughly 5mV accuracy. The trigger level was put at least 10 mV above the noise level.
| Strings | 1-4 | 11-13 | 14-19 |