[DVN_PRD] Deviation of a period

Function block DVN_PRD determines the deviation of an analog value above or below a range within a specific time period. The deviation is integrated via time.

DVN_PRD determines the deviation of an analog value above or below a range within a specific time period. The deviation is integrated via time.

Functioning

Enable and disable the function

The setpoint deviation of the analog input [In] above and below the range is determined within a time period if the function is enabled (EnFnct and EnEvl = 1) and the analog input is reliable (Vldty = 1).
The deviation is integrated via time.

Calculation

The deviation for the present time period is displayed on [PrHiVal] and [PrLoVal], where a negative deviation below the setpoint is assigned a negative sign for differentiation. After the time period has expired, the present upper and lower deviation is saved as upper and lower deviation from the recent time period [RctHiVal] and [RctLoVal] via a pulse. The start value at the outputs [PrxxVal] is calculated after a pulse via (1/3600) x (xxLm - In). No deviation is integrated if the analog value is within the limit value range [HiLm] and [LoLm]. The time period, generated outside of DVN_PRD, is determined via a rising slope on input [Imp]. If the input signal is invalid (Vldty = 0), the calculation stops. The last valid values from the outputs are frozen until the signal is valid again.

Subperiods within time periods

Input [EnEvl] can be used to evaluate subperiods within the entire time period. When EnEvl = 0, the evaluation is disabled and the last valid values are displayed at the outputs. At a pulse, the present upper and lower deviation are saved as values from the recent time period.

Reset

All present and recent values are set to zero via a rising slope on input [Reset].

Pins

Input	Description	Data type	Default value Value range
EnFnct	Enable function Enables the function.	Boolean	1
EnFnct	0 - The function is disabled. 1 - The function is enabled.
EnEvl	Enable evaluation	Boolean	1
EnEvl	0 - Evaluation is disabled and the valid values at the outputs are frozen. 1 - Evaluation is enabled.
In	Input Input signal	Real	0.0
Imp	Impulse Pulse input for which the evaluation time period is determined. Rising edge indicates start of new period.	Boolean	0
Imp	0 - No 1 - Yes
Vldty	Validity The deviation from the present and recent time periods can only be calculated with a valid input signal.	Boolean	1
Vldty	0 - Input signal is not valid. 1 - Input signal is valid.
HiLm	High limit	Real	23.0
LoLm	Low limit	Real	21.0
Reset	Reset	Boolean	0
Reset	0 - No 1 - Yes
Pers	Persistent	Boolean	0
Pers	0 - No 1 - Yes: the values are stored persistently.
TshVal	Threshold value	Real	0.1
BaObjRef	BA-Object reference Link between function block and BACnet object.	Structure	---
BaObjRef > DeviceID	Device identifier [DeviceID] includes object type and object instance in one ID. Identifies the device object: local or remote. A local device object can also be identified by value 16#3FFFFF.	Double Word	16#3FFFFF
BaObjRef > ObjectID	Object identifier [ObjectID] includes object type and object instance in one ID. Identifies the object on a device.	Double Word	16#3FFFFF
BaObjRef > ItemID	Item identifier [ItemID] represents an index in a view node object that references the BACnet object. [ObjectID] and [ItemID] together define an indirect reference to the BACnet object. Value -1 indicates a direct interface.	Integer	-1

Output	Description	Data type	Default value Value range
PrHiVal	Present high value	Real	0.0
RctHiVal	Recent high value	Real	0.0
PrLoVal	Present low value Negative sign for differentiation purposes	Real	0.0
RctLoVal	Recent low value Negative sign for differentiation purposes	Real	0.0
Dstb	Disturbed [Dstb] indicates whether the referenced BACnet object was accessed. [Dstb] = 0, if: BACnet object access = Access successful [Dstb] = 1, if: BACnet object access = Error during access	Boolean	0
ErrCode	Error code indication	Integer	0: No error
ErrCode	= 0 - No error > 0 - Error codes

Application

DVN_PRD is used to calculate the upper and lower deviation for an analog input value from a limit value range within a time period. The deviation is integrated via time. In the event of a constant deviation of 1 K over a time period (1 hour), the deviation is 1K/h. The deviation may also be 2 K for just 0.5 hours which results again in the integrated deviation of 1K/h.
By determining a setpoint deviation over a specific time period, errors, such as wrong control parameters, setpoint violations, or manual intervention, can be found earlier and faster.

The following example is based on an evaluation period = 1 day: