Detectors

There is a second table DET_CONF which tells the software about the configuration of your detector. The following example contains a group of entries from each of the big collaborations that use the software.

 
Table: Configuration table for detectors  

1. DET_SPEC contains attribute names of detectors in your tables. These so-called 'detector specifications' may be used to address single detectors or groups of them. In the example above, 'sig_land' indicates one photomultiplier of the LAND detector (which provides one analog signal, hence the name), 'det_land' indicates a paddle with its two PMTs, and 'n_plane' indicates a plane consisting of 20 paddles. 'sig_pla' is the attribute for one photomultiplier of the external plastic wall of the FOPI-collaboration, 'det_pla' is the attribute for a strip, and 'sector' is the attribute for the eight sectors. 'pmt_tof' indicates one photomultiplier of the time-of-flight wall of the ALADiN-collaboration, and '8pack' indicates a group of eight PMTs, either the top or the bottom of a module which consists of eight scintillator strips.
2. HV_SPEC tells our software which of the above detector specifications is key attribute of the high voltages. In the LAND detector, every PMT gets its own high voltage, therefore HV_SPEC = 'self' for 'sig_land', and for the others, HV_SPEC = 'sig_land'. In the plastic wall, two PMTs of one strip share a common high voltage from the LeCroy main frame (fine tuning is done by hand with potentiometers, but the CAMAC software does not know that), therefore HV_SPEC = 'self' for 'det_pla' and 'det_pla' for the other two detector specifications. The ALADiN-collaboration gives common high voltages to eight PMTs at the top and the bottom end of their eight-packs in the time-of-flight wall, therefore HV_SPEC = 'self' for '8pack', and it points towards '8pack' for 'pmt_tof'.
3. HV_LEN is the length of a HV vector for the detectors in question. This feature is handy if you have a detector which needs more than one voltage, and which may get damaged if you do not apply all of them at a time : If the voltages DEM_HV and MSR_HV (and the addresses MFRSLOT and MFRADDR for that detector) are vectors, you have to work hard to avoid switching all of them at a time. The maximum value of HV_LEN is eight.
4. SIG_SPEC identifies the attribute which indicates single detectors, i.e. analog signals. They are the smallest unit that can be addressed by the software in several ways: 'sig_land', 'sig_pla', and 'pmt_tof' are supposed to receive one value of constant fraction threshold or walk setting, there is one set of electronics addresses (TDC and/or QDC) in the database, and the tables might contain one value of default calibration factors (pedestals, gains) per signal.
5. HV_CTRL contains the identifier of the CAMAC controller that is used for the high voltages. This identifier has to show up in the table ELECLOC which contains locations of electronics modules and which will be introduced below.

You may wonder why attributes like 'sector' or 'n_plane' need to have a pointer both to the HV key attributes and to the signal attributes. The simple reason is that you may want to read some set-up parameter - e.g. CFD thresholds - for one sector of the FOPI-plastic wall, and the software then needs to generate a list of the signals that are members of that sector. Analogously, when you want to modify the high voltages of that sector, the software needs a list of the appropriate strips.

You should be aware that the grouping of signals into subunits by DET_SPEC and SIG_SPEC is not poured in concrete, but is to a large extent a matter of taste. The BaF-detectors of the LAND collaboration provide a nice example: Their signals are fed into three electronics modules, a CFD & TDC for time information, and two QDCs with a short and a long gate for energy information. Softwarewise, each paddle of that detector, called 'det_tdet', was listed as two 'sig_tdet', one of them with a TDC and a QDC address (for the short gate), and the second one with a QDC address only (for the long gate). In that configuration, 'sig_tdet' was considered a single detector, and the physical paddles called 'det_tdet' were used to control the high voltages. Alternatively, one could have provided 'sig_tdet' with three addresses, and one could at the same time have used them as key attributes for the HV.