Supported platforms: CODESYS 3.5 SAFETY

S_CurrentRequestLimiter (FUN)

 

This POU exists in library version 2.0.1.0 or newer.

 

Description

 

This function limits the current request value between given minimum and maximum currents.

 

Operation

POU is in normal operation mode if:

• The operation is enabled, i.e. i_Enable is TRUE AND
• The input current minimum and maximum parameters are valid, i.e. S_i_MinimumCurrent < S_MaximumCurrent

 

In normal operation POU set S_i_CurrentRequest value to output S_o_CurrentRequest if:

• S_i_CurrentRequest = 0 OR
• S_i_MinimumCurrent ≤ S_i_CurrentRequest ≤ S_MaximumCurrent 

 

POU set S_i_MinimumCurrent value to output S_o_CurrentRequest and output o_InputLow true if:

• 0 < S_i_CurrentRequest < S_i_MinimumCurrent 

 

POU set S_i_MaximumCurrent value to output S_o_CurrentRequest and output o_InputHigh true if:

• S_i_CurrentRequest > S_i_MaximumCurrent

 

The output o_OutputValid is always true in normal operation mode.

The outputs o_InputLow and o_InputHigh are set to false automatically, when  S_i_MinimumCurrent ≤ S_i_CurrentRequest ≤ S_MaximumCurrent.

 

Operation in fault situations

The output S_o_CurrentRequest is set to 0, o_OutputValid is set to false and o_ParameterError is set to true, if: 

• S_i_MinimumCurrent ≥ S_MaximumCurrent AND i_Enable is TRUE.

 

Error is reset when S_i_MinimumCurrent <  S_MaximumCurrent. The rising edge of i_Enable signal is not required. 
 

Inputs

Input variable name	Data type	Unit	Range	Description
i_Enable	BOOL		-	Enable POU operation
S_i_CurrentRequest	SAFEUINT	mA	-	Current request
S_i_MinimumCurrent	SAFEUINT	mA	-	Minimum allowed current
S_i_MaximumCurrent	SAFEUINT	mA	-	Maximum allowed current

 

Outputs

Output variable name	Data type	Unit	Range	Description
S_o_CurrentRequest	SAFEUINT	mA	-	Current request
o_OutputValid	BOOL		-	Current request is valid
o_InputHigh	BOOL		-	Input current request is too high
o_InputLow	BOOL		-	Input current request is too low
o_ParameterError	BOOL		-	Parameter error is active

 

Error diagnostic

Conditions	S_o_CurrentRequest	OutputValid	InputHigh	InputLow	ParameterError
i_Enable = FALSE	0	FALSE	FALSE	FALSE	FALSE
i_Enable = TRUE AND S_i_MinimumCurrent ≥ S_i_MaximumCurrent	0	FALSE	FALSE	FALSE	TRUE
i_Enable = TRUE AND Parameter Ok AND S_i_CurrentRequest > 0 AND S_i_CurrentRequest < S_i_MinimumCurrent	S_i_MinimumCurrent	TRUE	FALSE	TRUE	FALSE
i_Enable = TRUE AND Parameter Ok AND S_i_CurrentRequest > S_i_MaximumCurrent	S_i_MaximumCurrent	TRUE	TRUE	FALSE	FALSE
i_Enable = TRUE AND  Parameter Ok AND S_i_CurrentRequest = 0	S_i_CurrentRequest	TRUE	FALSE	FALSE	FALSE
i_Enable = TRUE AND  Parameter Ok AND  S_i_MinimumCurrent ≤ S_i_CurrentRequest ≤ S_i_MaximumCurrent	S_i_CurrentRequest	TRUE	FALSE	FALSE	FALSE

 

See also

• How to control proportional valves

 

 

 

 

Source file S_CurrentRequestLimiter.htm

Last updated 4-Sep-2025