Attribute alarms

Attribute alarms#

audience:all

Tango provides an automatic way of defining alarms. An alarm condition will switch the attribute quality factor to alarm and the device state will automatically switched to ALARM in certain conditions. Four properties are available for alarm purpose.

For example the voltage of a powersupply set via a DAC and read via an ADC convertor. Both values can be different due to various factors such as internal resistor or noise on the ADC. Additionally the powersupply may need a certain time to establish its output voltage when changing the set point. The Tango alarm system is able to handle the acceptable noise threshold and the time the device needs to establish the voltage after the writing of the setpoint (time constant).

The level alarms#

This alarm is defined for all Tango attribute read type and for numerical data type. The action of this alarm depend on the attribute value when it is read :

  • If the attribute value is below or equal the attribute configuration min_alarm parameter, the attribute quality factor is switched to Tango::ATTR_ALARM and if the device state is Tango::ON, it is switched to Tango::ALARM.

  • If the attribute value is below or equal the attribute configuration min_warning parameter, the attribute quality factor is switched to Tango::ATTR_WARNING and if the device state is Tango::ON, it is switched to Tango::ALARM.

  • If the attribute value is above or equal the attribute configuration max_warning parameter, the attribute quality factor is switched to Tango::ATTR_WARNING and if the device state is Tango::ON, it is switched to Tango::ALARM.

  • If the attribute value is above or equal the attribute configuration max_alarm parameter, the attribute quality factor is switched to Tango::ATTR_ALARM and if the device state is Tango::ON, it is switched to Tango::ALARM.

If the attribute is a spectrum or an image, then the alarm is set if any one of the attribute value satisfies the above criterium. By default, these four parameters are not defined and no check will be done.

The following figure is a drawing of attribute quality factor and device state values function of the the attribute value.

Level alarm

Figure 7.1: Level alarm#

If the min_warning and max_warning parameters are not set, the attribute quality factor will simply change between Tango::ATTR_ALARM and Tango::ATTR_VALID function of the attribute value.

Warning

The behaviour described above is only correct in the case the device’s method Tango::Device_[X]Impl::dev_state() is executed*.* In case of overwrite of the dev_state() in the device code, it is recommended to finish the method by calling DeviceImpl::dev_state();

Warning

min_warning and max_warning : lower and upper bound for WARNING (deprecated since version 8)

The Read Different than Set (RDS) alarm#

This alarm is defined only for attribute of the Tango::READ_WRITE and Tango::READ_WITH_WRITE read/write type and for numerical data type. This is very useful to handle maximum noise in constant time.

This alarm configuration is done with two attribute configuration parameters:

  • delta_val and delta_t Valid for a writeable attribute. Define a maximum difference between the set_value and the read_value of an attribute after a standard time. By default, these two parameters are not defined and no check will be done.

When the attribute is read (or when the device state is requested), if the difference between its read value and the last written value is something more than or equal to an authorized delta and if at least a certain amount of milli seconds occurs since the last write operation, the attribute quality factor will be set to Tango::ATTR_ALARM and if the device state is Tango::ON, it is switched to Tango::ALARM.

If the attribute is a spectrum or an image, then the alarm is set if any one of the attribute value’s satisfies the above criterium.