Trend Log/BACnet Trend Log

Transcription

1 Object Dictionary 1 Trend Log/BACnet Trend Log Introduction Notes: The Johnson Controls Trend Log object is considered a BACnet Trend Log object because it supports BACnet functionality. In addition, this object has Johnson Controls proprietary attributes. The Johnson Controls Trend Log object only supports trending of numeric data type values and does not support intrinsic alarming. The Trend Log object monitors and records the changes in the behavior of an individual attribute over time, thereby assisting you with diagnosing various system-wide behavioral characteristics. The Trend Log object collects sample values at timed intervals or only upon changes in the given value. A Trend Log object is used to collect data from the Analog Input object of a controller on the N2 Bus, which reports information such as outdoor air temperature or room air temperature. See the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE) Standard for information on this object and the BACnet communication standard. May 1, 2002 Johnson Controls, Inc. Code No. LIT Software Release 5.1

2 2 Trend Log/BACnet Trend Log Key Concepts Trending The Trend Log object monitors an attribute of a referenced object and, when predefined conditions are met, saves (logs) the value of the attribute and a timestamp in an internal buffer for subsequent retrieval. The referenced object can reside either in the same device as the Trend Log object or in an external device. The Trend Log object records the referenced object attribute value upon either Change of Value (COV) subscription or periodic poll. Where status flags are available (such as when the COV Notification or Read Property Multiple services are used), they also are acquired and saved with the data. Trend Log also records Errors that prevent the acquisition of the data, as well as changes in the status or operation of the logging process itself. Each time-stamped buffer entry is called a Trend Log record. Each Trend Log object maintains an internal, optionally fixed-size buffer. This buffer fills or grows as log records are added. If the buffer becomes full, either the least recent record is overwritten when a new record is added or collection is set to stop. Trend Log records are transferred as BACnet Log Records using the Read Range service. The buffer may be cleared by writing a zero to the Record Count attribute. The log records can store several data types. The ability to store Any data types is optional. You can restrict the data stored in the log buffer to 32 bits, as in the case of bit strings, to facilitate implementation in devices with strict storage requirements. Each N30 sample is 72 bits (timestamp = 4 bytes, value = 4 bytes, and status = 1 byte). Use the Log Enable property to enable or disable logging at the dates and times specified by the Start Time and Stop Time properties. The log buffer records Trend Log enabling and disabling. Event reporting (notification) facilitates automatic fetching of log records by processes on other devices such as fileservers. The Trend Log object supports algorithmic reporting. In response to a notification, subscribers fetch the new records with a Read Range service request using the Current Notify Time of the preceding notification as the Beginning Date parameter and the Current Notify Time of the current notification as the Ending Date parameter. A subscriber may detect a missed notification if the Current Notify Time it received in its previous notification is older than the Previous Notify Time parameter of the current notification. If the Firstitem flag of the Read Range-ACK response to the Read Range request issued under these conditions sets to True, Trend Log records have probably been missed by this subscriber.

3 Object Dictionary 3 Log Buffer Values The acquisition of log records by remote devices has no effect upon the state of the Trend Log object itself. This allows completely independent, but properly sequential, access to its log records by all remote devices. Any remote device can independently update its records at any time. Each time-stamped record in the Log Buffer attribute contains the data fields in Table 1. Table 1: Data Fields Data Field Timestamp Log Datum Status Flags Description The date and time, in Universal Time Coordinated (UTC), when the record was collected The data value read from the monitored object and attribute, an error encountered in an attempt to read a value, or a change in status or operation of the Trend Log object itself. See Table 2. The Status Flags attribute of the monitored object, if present and available, automatically is associated with the Log Datum data value. If the Status Flags attribute is not present or not available, this item is not included in the log record.

4 4 Trend Log/BACnet Trend Log Table 2: Log Datum Values Value Log-Status Boolean-Value Float-Value Enum-Value Unsigned-Value Signed-Value Bitstring-Value Null-Value Failure Time-Change Any-Value Description This choice represents a change in the status or operation of the Trend Log object. Whenever one of the events represented by the flags listed below occurs, except as noted, a record is appended to the buffer. Log-disabled: This flag is set whenever the Trend Log object is disabled, such as when Log Enable is False. Whenever the Trend Log object begins operation, this flag changes from True to False and a log entry is made. Buffer-purged: This flag is set to True whenever the buffer is deleted by a write of zero to the Record Count attribute. After this value is recorded in the buffer, the subsequent immediate change to False is not recorded. These choices represent data values read from the monitored object and property. This choice represents an error encountered in an attempt to read a data value from the monitored object. If an error response from a remote device conveys the error, the Error Class and Error Code in the response are recorded. This choice represents a change in the clock setting in the device. It records the number of seconds that the clock changed. If the number is unknown, such as when the clock is initialized for the first time, the value recorded is zero. This choice represents data values read from the monitored object and attribute.

5 Object Dictionary 5 Attributes Specific Attributes Table 3: Attribute Properties The attributes specific to the Trend Log object are listed in Table 3. The Trend Log object also has the attributes of the Metasys Common object. Refer to Table 1 in the Metasys Common Object chapter (LIT ) for details. Attribute Name Data Type N30 Flags* M-Series Flags* N30 Default Value Options/Range Metasys Common Attributes See Table 1 in the Metasys Common Object chapter (LIT ). BACnet Required Attributes Buffer Size Unsigned C W Event State Enumeration W Always Normal Log Buffer List W Log Enable Boolean W DW False Object Identifier BACnet Object ID C Record Count Unsigned CDW DW Stop When Full Boolean CW W False Total Record Count Unsigned Long W BACnet Optional Attributes Acked Bit String W To-Normal To-Fault, To-Normal Transitions 1 Client COV Increment Enumeration NW COV Resubscription Interval Unsigned W Current Notify Enumeration W Time 1 Event Enable 1 Bit String W To-Normal To-Fault, To-Normal Event Time Stamps Array Continued on next page... * C - Configurable, D - Default Attribute, N - Value Not Required, W - Writable 1 These attributes support intrinsic reporting.

6 6 Trend Log/BACnet Trend Log Attribute Name (Cont.) Log Device Object Property 2 Log Interval 2 Data Type Object Reference Unsigned Long N30 Flags* M-Series Flags* N30 Default Value BACnet Optional Attributes (Cont.) Options/Range CW W 600 Minimum Value = 0 Maximum Value = Units = Seconds Notification Class 1 Unsigned W The BACnet Object Identifier of the Notification Class object used for routing Notification Unsigned W Threshold 1 Notify Type 1 Enumeration W Alarm, Event Previous Notify Time 1 Date/Time W Profile Name This BACnet optional attribute is not supported. Records Since Unsigned W Notification 1 Start Time 2 Date/Time W Stop Time 2 Date/Time W Johnson Controls Proprietary Attributes Execution Trigger Boolean W W Input Reference Attribute Reference C W * C - Configurable, D - Default Attribute, N - Value Not Required, R - Association to Reliability, W - Writable 1 These attributes support intrinsic reporting. 2 At least one of these attributes is required.

7 Object Dictionary 7 Attribute Definitions Table 4: Attribute Definitions Attribute Name Metasys Common Attributes Buffer Size Event State Log Buffer Log Enable Object Identifier Record Count Stop When Full Table 4 lists the definitions of the attributes specific to the Trend Log object. Definition See Table 2 in the Metasys Common Object chapter (LIT ). BACnet Required Attributes Specifies the maximum number of records the buffer may hold. This value is entered/modified only when adding a new Trend Log object. Determines if an active event state is associated with this object. If the object supports intrinsic reporting, then the Event State attribute indicates the event state of the object. If the object does not support intrinsic reporting, the value of this attribute is Normal. The allowed states are Normal and Fault. For BACnet compatibility with intrinsic reporting, this attribute is always set to normal. Lists Buffer Size timestamped records of data type BACnet Log Record. Each record conveys a recorded data value, an error related to data collection, or status changes in the Trend Log object. See Table 1 and Table 2. The buffer is not network accessible except through the use of the Read Range service with implicit reference to the Trend Log. Indicates and controls whether (True) or not (False) logging is enabled. A False value overrides the time interval defined by Start Time and Stop Time. If logging is otherwise enabled by the Start Time and Stop Time attributes, changes to Log Enable are recorded in the log. When the device begins operation, the value True is recorded in the log. Identifies the object with a unique numeric code. Represents the number of records currently resident in the log buffer. A value of zero for this attribute deletes all records in the log buffer and resets Records Since Notification to zero. Upon completion, this event is reported in the log as the initial entry. Specifies whether (True) or not (False) logging should cease when the buffer is full. When logging ceases, Log Enable sets to False. Total Record Count Represents the total number of records collected by the Trend Log object since creation. When the value of Total Record Count reaches its maximum possible value of , the next value it takes is zero. Once this value has wrapped to zero, its semantic value (the total number of records collected) is lost, but its use in generating notifications remains. Continued on next page...

8 8 Trend Log/BACnet Trend Log Attribute Name (Cont.) Acked Transitions Client COV Increment COV Resubscription Interval Current Notify Time Event Enable Log Device Object Property Log Interval Notification Class Notification Threshold Definition BACnet Optional Attributes Conveys three flags that separately indicate the receipt of acknowledgements for To-Fault and To-Normal events. These flags clear upon the occurrence of the corresponding event and set under any of these conditions: upon receipt of the corresponding acknowledgement upon the occurrence of the event if the corresponding flag is not set in the Event Enable attribute (meaning event notifications are not generated for this condition and thus no acknowledgement is expected) upon the occurrence of the event if the corresponding flag is set in the Event Enable attribute and the corresponding flag in the Ack Required attribute of the Notification Class object implicitly referenced by the Notification Class attribute of this object is not set (meaning no acknowledgement is expected) If the Trend Log is acquiring COV data, this attribute specifies the increment used in determining that a change of value has occurred. If the referenced object and attribute supports COV reporting, this attribute has a Null value. If the Trend Log acquires data from a remote device by COV subscription, this attribute specifies the number of seconds between COV resubscriptions, if COV subscription is in effect. Subscribe COV requests specify twice this lifetime for the subscription and specify the issuance of confirmed notifications. If COV subscriptions are in effect, the first COV subscription issues when the Trend Log object begins operation or when Log Enable becomes True. If present, the value of this attribute must be non-zero. If this attribute is not present, then COV subscription should not be attempted. Represents the timestamp associated with the most recently collected record whose collection triggered a notification. If no notification has occurred since logging began, this property contains all wildcard values. This property is required if the object supports intrinsic reporting. Conveys three flags that separately enable and disable reporting of To-Fault and To-Normal events. In the context of Trend Log objects, the value of the Records Since Notification attribute becoming equal to or greater than the value of Notification Threshold causes a Normal-Normal transition. The failure of an attempted COV subscription causes a To Fault state transition. The To Normal transition must be enabled when intrinsic reporting is used; this is set by default. This property is required if the object supports intrinsic reporting. Specifies the Device Identifier, Object Identifier, and Property Identifier of the attribute to be trend logged. If this attribute is writable, it may be restricted to reference only objects inside the device containing the Trend Log object. If the attribute is restricted to referencing objects within the containing device, an attempt to write a reference to an object outside the containing device into this attribute causes a Result (-) to be returned. Specifies the periodic time in seconds for which the referenced property is logged. If this attribute is zero, then the Trend Log issues COV subscriptions for the referenced attribute. The value of this attribute must be non-zero if COV Resubscription Interval is not present. This attribute must be writable if present. Specifies the notification class used when handling and generating event notifications for this object. The Notification Class attribute implicitly refers to a Notification Class object that has a Notification Class attribute with the same value. This property is required if the object supports intrinsic reporting. Specifies the value of Records Since Notification at which notification occurs. This property is required if the object supports intrinsic reporting. Notify Type Conveys whether the notifications generated by the object are Events or Alarms. This attribute is required if the object supports intrinsic reporting. Continued on next page...

9 Object Dictionary 9 Attribute Name (Cont.) Previous Notify Time Records Since Notification Start Time Stop Time Execution Trigger Input Reference Definition BACnet Optional Attributes (Cont.) Represents the value of the Current Notify Time attribute at the time of the previous notification. At the beginning of a notification operation, this attribute sets to the value of Current Notify Time, then the attribute Current Notify Time is updated. If no previous notification has occurred, this property contains all wildcard values. This property is required if the object supports intrinsic reporting. Represents the number of records collected since the previous notification or beginning of logging if no previous notification has occurred. This property is required if the object supports intrinsic reporting. Specifies the date and time at or after which logging is enabled by this attribute. If any of the fields of the BACnet Date Time contain wildcard values, then the conditions for logging to be enabled by Start Time are ignored. If Start Time specifies a date and time after Stop Time, then logging is disabled. This attribute must be writable if present. Specifies the date and time at or after which logging is disabled by this attribute. If any of the fields of the BACnet Date Time contain wildcard values, then the conditions for logging to be enabled by Stop Time are ignored. If Stop Time specifies a date and time earlier than Start Time, then logging is disabled. This attribute must be writable if present. Johnson Controls Proprietary Attributes When a process or user writes this attribute to True, the Trend Log object takes a sample and resets the attribute to False. Defines the attribute of the object being sampled. This attribute is used for consistent references to an object or attribute. The Input Reference and the name of the object and attribute you want to trend must match exactly. If you add a Trend Log object while the object you want to trend is selected, the Input Reference field fills in automatically. Commands The Trend Log object supports the commands listed in Table 5. The order of the commands in the table reflects how the commands appear on the user interface. Table 5: Supported Commands Command Name Parameters Access Level Description Display Operate Allows a trend log to be displayed on the active user interface. Print The printer to which the trend log is Operate Directs a trend log to be printed at an identified printer. being sent. Enable Modify Resumes collection of samples. Disable Modify Stops collection of samples. Controls Group 507 E. Michigan Street P.O. Box 423 Milwaukee, WI Printed in U.S.A.