Alarm Formulas Examples ¶

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Alarm Formulas Examples

Alarms are parsed and evaluated using fandango.TangoEval class.

Sending a Test Message at Startup ¶

This alarm formula is just “True” ; therefore will be enabled immediately sendin an email message to test@tester.com

AlarmList -> DEBUG:True
AlarmDescriptions -> DEBUG:The PyAlarm Device $NAME has been restarted
AlarmReceivers -> DEBUG: test@tester.com

Testing a device availability ¶

It is done if you put directly the name of the device or its State as a condition by itself. In the second case and alarm will be triggered either if the Pressure is above threshold or the device is not reachable.

PRESSURE:SR/VC/VGCT/Pressure > 1e-4
STATE_AND_PRESSURE:?SR/VC/VGCT and SR/VC/VGCT/Pressure > 1e-4

Getting Tango state/attribute/value/quality/time/delta in formulas ¶

The Alarm syntax allows to add the following clauses to the attribute name (value returned by default):

some/device/name{/attribute}{.value/all/time/quality/delta/exception}

attribute: if no attribute name is given, then device state is read.

PLC_Alarm: BL22/CT/EPS-PLC-01 == FAULT

value: default, returns the value of the attribute

Pressure_Alarm: BL22/CT/EPS-PLC-01/CC1_AF.value > 1e-5

time: returns the epoch in seconds of the last value read

Not_Updated: BL22/CT/EPS-PLC-01/CPU_Status.time < (now-60)

quality : returns the tango quality value (ATTR_VALID, ATTR_INVALID, ATTR_WARNING, ATTR_ALARM).

Temperature_Alarm: BL22/CT/EPS-PLC-01/OP_WBAT_OH01_01_TC11.quality == ATTR_ALARM

delta : returns the variation of the value in the last N=AlarmThreshold reads (stored in TangoEval.cache array of size AlarmThreshold+1)

Valve_Just_Closed: BL22/CT/EPS-PLC-01/VALVE_11.delta == -1

exception : True if the attribute is unreadable, False otherwise

Not_Found: BL22/CT/EPS-PLC-01/I_Dont_Exist.exception

all : returns the raw attribute object as returned by PyTango.DeviceProxy.read_attribute method.

Creating a periodic self-reset alarm ¶

A simple clock alarm would use the current time and will set AlarmThreshold, PollingPeriod and AutoReset properties. See this example:

https://github.com/tango-controls/PANIC/blob/documentation/doc/recipes/CustomAlarms.rst#clock-alarm-triggered-by-time

A single formula clock would be more hackish; this alarm will execute a command on its own formula

PERIODIC:(FrontEnds/VC/Elotech-01/Temperature and FrontEnds/VC/VGCT-01/P1 \
and (1920<(now%3600)<3200)) or (ResetAlarm('PERIODIC') and False)

Enabling search, expression matching and list comprehensions ¶

Having the syntax dom/fam/mem/attr.quality whould allow us to call attrs like:

any([ATTR_ALARM==s+'.quality' for s in FIND('dom/fam/*/pressure')])

One way may be using QUALITY, VALUE, TIME key functions:

any([ATTR_ALARM==QUALITY(s) for s in FIND('dom/fam/*/pressure')])

The use of FIND allows PyAlarm to prepare a list Taurus models that can be redirected from an <pre>event_received(...)</pre> hook.

Some list comprehension examples ¶

any([s for s in FIND(SR/ID/SCW01/Cooler*Err*)])

equals to

any(FIND(SR/ID/SCW01/Cooler*Err*))

The negate:

any([s==0 for s in FIND(SR/ID/SCW01/Cooler*Err*)])

is equivalent to

any(not s for s in FIND(SR/ID/SCW01/Cooler*Err*)])

is equivalent to

not all(FIND(SR/ID/SCW01/Cooler*Err*))

is equivalent to

[s for s in FIND(SR/ID/SCW01/Cooler*Err*) if not s]

Grouping Alarms in Formulas ¶

The proper way is (for readability I use upper case letters for alarms):

ALARM_1: just/my/tango/attribute_1
ALARM_2: just/my/tango/attribute_2

then:

ALARM_1_OR_2: ALARM_1 or ALARM_2

or:

ALARM_1_OR_2: any(( ALARM_1 , ALARM_2 ))

or:

ALARM_ANY: any( FIND(my/alarm/device/ALARM_*) )

Any alarm you declare becomes both a PyAlarm attribute and a variable that you can anywhere (also in other PyAlarm devices). You don’t trigger any new read because you just use the result of the formula already evaluated.

The GROUP is used to tell you that a set of conditions has changed from its previous state. GROUP instead will be triggered not if any is True, but if any of them toggles to True. It forces you to put the whole path to the alarm:

GROUP(my/alarm/device/ALARM_[12])

Alarm on delta and value ¶

This alarm will be triggered whenever a channel (HV*Code attributes) changes its value (delta!=0) and the new value is OFF (value=0)

any([(changed and value==0) for changed,value in

zip( FIND(bl*/vc/ipct*/hv*code.delta) ,

FIND(bl*/vc/ipct*/hv*code.value) )])

Generating Clock Signals ¶

Playing with PollingPeriod, AlarmThreshold and AutoReset properties is possible to achieve an square signal that keeps the alarm active/inactive at regular intervals.

CLOCK=NOT CLOCK

The AlarmThreshold applies to both activation and reset of the alarm, so it has to be added to the AutoReset period to regulate the duty cycle. Keeping the PollingPeriod and AutoReset values very small will generate an accurate frequency (do not expect high accuracy, that’s a trick for testing but not a proper signal generator).

My values for a 10 seconds alarm cycle are:

.. code-block:: python

PollingPeriod = 0.1 AlarmThreshold = 50 AutoReset = 0.0001

If you want a more accurate alarm, you can also use the NOW() function. This example generates a switch every second

CLOCK = NOW()%2<1
PollingPeriod=1
AlarmThreshold-1

Alarm Formulas Examples ¶

Sending a Test Message at Startup ¶

Testing a device availability ¶

Getting Tango state/attribute/value/quality/time/delta in formulas ¶

Creating a periodic self-reset alarm ¶

Enabling search, expression matching and list comprehensions ¶

Some list comprehension examples ¶

Grouping Alarms in Formulas ¶

Alarm on delta and value ¶

Generating Clock Signals ¶

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