====== Single alarm memory with delay ======

{{:en:mervis-ide:35-help:bd56.png}}

===== Block name =====

BD56_SINGLEALARMMEMORYDELAY

===== ST call =====

<code st-iec>
PROGRAM TEST BD56
VAR 
  BOOL1,BOOL2,BOOL3,BOOL4,BOOL5 :BOOL;
    TIME1 : TIME;
   INT1:INT;
   FB : LIB.CORE.V1_1.BD56_SINGLEALARMMEMORYDELAY;
END_VAR
  FB(IN:=BOOL1,ACK:=BOOL2,RESET:=BOOL3,DELAY:=TIME1);
 BOOL4 := FB.ACKNOWLEDGED;
   BOOL5 := FB.MEMORY;
 INT1 := FB.ALRSTATUS;
END_PROGRAM
</code>

===== Library =====

LIB\CORE

===== Version =====

V1.1

===== Description =====

The block is an alarm memory which responds after a time delay only.\\


===== Inputs =====

|Input   |Type             |Description                                 |Default value|
|IN      |BOOL             |Alarm input                                 |False        |
|ACK     |BOOL             |Alarm acknowledge                           |False        |
|RESET   |BOOL             |Alarm memory reset                          |False        |
|DELAY   |TIME             |Alarm delay                                 |30s          |
|Priority|AlarmPriorityType|Assigned alarm priority, not used internally|50           |

===== Outputs =====

|Output      |Type|Description                                    |
|ACKNOWLEDGED|BOOL|Indication that the alarm has been acknowledged|
|MEMORY      |BOOL|Alarm memory                                   |
|ALRSTATUS   |INT |Alarm status                                   |

===== Function =====

The block is a memory block which keeps alarm status for display in SCADA or for interlocking of the controlled aggregates. After a rising edge on the //in// input the time delay is measured. If the input TRUE level lasts even after the //delay// time expires, the block goes into alarm, indicating alarm memory at the //memory// output. The alarm can be acknowledged either via SCADA or other client, or by bringing a rising edge to the //ack// input. Then, the //acknowledged// output goes to TRUE. After the alarm signal disappears (//in// goes to FALSE), the alarm can be reset by bringing a rising edge to the //reset1// or //reset2// inputs.

Values of //alrstatus//:

  * //alrstatus//=256 - at least one alarm is active\\

  * //alrstatus//=512 - at least one alarm has been //acknowledged//\\

  * //alrstatus//=1024 - //memory// = true, alarm is unacknowledged and unreset.

The //alrstatus// value may be a composition of more above mentioned indicators.\\


===== Application example =====

{{:en:mervis-ide:35-help:bd56_example.png}}\\
The alarm block is one of the most frequently used blocks in the HVAC control programs. It is used for safety interlock of pumps and fans, which are prevented from operation until their alarm blocks are reset manually over a HMI or SCADA (or by a general alarm reset button at the panel door).\\
\\