A safety feature of HV control

Of all the set-up parameters discussed here, high voltages are the only ones with which you can do real damage to your detector. In particular, there is always the risk that a COMIS routine which is used for automatic setting of high voltages goes haywire. The hazard is increased by the (convenient) command 'hvinc' which allows you to increase high voltages from their current value - if you lose track of your start value, you may wind up with values that are hazardous to the health of your PMTs. The software therefore contains maximum values of high voltages for certain types of PMTs. All your detectors have to have an attribute PMT_TYPE associated with them, and your database needs to contain a table called LIMITS, where an interval of high voltages is provided for each type of PMTs you use. The table LIMITS needs to have the attributes ITEM, MIN_VAL, and MAX_VAL. Whenever you write demand HVs to the front end, the attribute PMT_TYPE is used to get the interval of high voltages from table LIMITS, and if your demand value is out of range, you get an error message, and nothing happens. Example: The LAND detector is equipped with Valvo XP2262 tubes which are specified in column PMT_TYPE of table , and the table LIMITS contains an entry for XP2262 which limits the high voltages to -2500 V (table ).

 
Table: PMT types for the LAND detector  

 
Table: HV interval for Valvo XP2262 tubes in table LIMITS