[MIN_PRD] Minimum of a period

Function block MIN_PRD determines the minimum for an analog value within a specific time period.

MIN_PRD determines the minimum for an analog value within a specific time period.

Enable and disable the function

The minimum value of the analog input signal [In] is determined within a time period if the function is enabled (EnFnct and EnEvl = 1) and the analog input signal is reliable (Vldty = 1).

Calculation

The minimum value for the present time period is displayed on [PrVal]. After the time period has expired, the minimum value is saved as the minimum value of the recent time period via a pulse at [RctVal]. The pending input value is set as new minimum value.
The time period, generated outside of MIN_PRD, 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.

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 minimum value is saved as a minimum value from the last time period.

Reset

Via a rising slope at input [Reset] and a valid input signal (Vldty = 1), the present value [PrVal] takes the valid input value and the recent minimum value [RctVal] is set to zero.
With a [Reset] and an invalid input signal (Vldty = 0) and/or EnEvl = 0, the [PrVal] is set to + infinity and [RctVal] to zero.

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. The rising edge indicates start of new period.	Boolean	0
Imp	0 - No 1 - Yes
Vldty	Validity The present minimum value and minimum value from 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.
Reset	Reset	Boolean	0
Reset	0 - No 1 - Yes
Pers	Persistent	Boolean	0
Pers	0 - No 1 - Yes: the values are stored persistently.
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
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

MIN_PRD is used to calculate the minimum value for a time period. By displaying present and recent minimum values from a particular time period, errors, such as wrong control parameters, setpoint violations, or manual intervention can be identified earlier and faster.

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