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electronics [2013/10/24 10:21]
pereira |
electronics [2013/10/31 09:17]
pereira old revision restored (2013/10/24 10:49) |
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| ===== Trigger Box ===== | ===== Trigger Box ===== |
| In addition to the singles and coincidence triggers, two separate inputs called "External 1" and "External 2" can be used as trigger sources. All sources can be independently selected by selecting the appropriate check box in the trigger box (see figure above), which is a logical OR of all five inputs. This means in case more than one trigger source is selected, it is possible that more than one pulse is generated at the output, depending on the timing and shape of the source signals. When both downscaled singles and coincidences are selected for instance, the "Raw trigger" output of the trigger box may generate two pulses for a single event. A scaler connected to the "Raw trigger" output will therefore not reflect the true number of events. For this reason scalers are also connected to individual inputs of the trigger box. A trigger register word (bit pattern) is written at each occurrence of a live trigger signal. This word is the first being read out from the trigger module, prior to the time stamp. | In addition to the singles and coincidence triggers, two separate trigger sources labeled "External 1" and "External 2" can be used. The various sources can be selected from the trigger box to define the raw trigger, which is then sent to a third AND gate for computer busy rejection. The busy latch (on the middle) is set by the raw trigger after a 50ns delay, and prevents subsequent events to be accepted. It is reset by the computer once the current event has been processed. The live trigger signal is fed to gate generators used to generate appropriate gates for the ADCs, QDCs, TDCs and an eventual coincidence register. Note that the trigger box contains its own coincidence register for which the input signals are delayed by 50ns, and the gate width is set by the coincidence gate generator. The request event signal is latched before being sent to the computer. |
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| | Since more than one trigger source can be selected, it is possible that more than one pulse is generated at the output of the trigger box, depending on the timing and shape of the source signals. When both downscaled singles and coincidences are selected for instance, the "Raw trigger" output of the trigger box may generate two pulses for a single event. A scaler connected to the "Raw trigger" output will therefore not reflect the true number of events. For this reason scalers are also connected to individual inputs of the trigger box. A trigger register word (bit pattern) is written at each occurrence of a live trigger signal. This word is the first being read out from the trigger module, prior to the time stamp. |
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