[DIFFPRDR] Difference of a period for real values

Function block DIFFPRDR determines the differential value for a real counter value within a specific time period.

DIFFPRDR determines the differential value for a real counter value within a specific time period.

Enable and disable the function

The differential value of a counter value [In] within a time period is determined if the function is enabled (EnFnct = 1 and Imp = 1). The function does not start with [EnFnct] only. A pulse at [Imp] is required to start the function.

Calculation

The differential value for the present time period is displayed on [PrVal]. After the time period has expired, the present differential value is saved as differential value for the recent time period [RctVal] and set to zero via a pulse. The time period, generated outside of DIFFPRDR, is determined via a rising slope on the 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. If the input value is smaller than the differential value saved at a pulse, the difference becomes invalid. If the signal or the differential value is invalid at pulse time, no valid difference can be generated for the next two time periods. This information is provided at output [VldtyDly].

Reset

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

Startup

First time period: After the first pulse, the present value at input [In] is saved as reference for a further differential value generation. After the pulse, [VldtyDly] = 1 after a delay (25 AS cycles). From the first pulse, a difference is generated on output [PrVal] for an increasing counter value at input [In].

Second time period: After the second pulse, the present differential value is saved as differential value on [PrVal] for the recent time period [RctVal] and set to zero.

For a time period of 1 day, a differential value that can be evaluated and provided only after the 2nd pulse (after 2 days).
If a full download is performed, all values are reset and data may be lost as a consequence.

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.
In	Input Input signal	Real	0.0
Imp	Impulse Pulse input for which the evaluation time period is determined. The rising edge indicates start of new period.	Boolean	0
Imp	0 - No 1 - Yes
Vldty	Validity The differential value from the present and recent time periods can only be calculated with a valid input signal.	Boolean	1
Vldty	0 - The input signal is not valid. 1 - The input signal is valid.
Reset	Reset All values are reset to zero.	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
PrVal	Present value	Real	0.0
RctVal	Recent value	Real	0.0
VldtyDly	Validity with delay	Boolean	0
VldtyDly	0 - Not valid 1 - Valid
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

DIFFPRDR is used to calculate the differential value derived from the counter status within a time period. By displaying present and recent values, daily consumption, for example, can be calculated for a specific time period.

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