S_NTCSensor

Supported platforms: CODESYS 3.5 SP19 SAFETY

S_NTCSensor (FUN)

Description

This function converts resistance value to temperature (°C). POU’s operational range is at least from -50 ℃ to 150 ℃. This POU can be used for NTC type temperature sensors.

Function uses beta parameter equation to calculate temperature from resistance value.

, where T25 = 298,15 K and T0 = 273,15 K.

Sensor hardware errors are diagnosed with SafeConversion library's function blocks S_ADCToVoltageOrCurrent or S_VoltageToResistance.

Sensor value alarms and warnings are diagnosed with SafeDataValidation library function block S_ValueDiagnostic.

Inputs

Input variable name	Data type	Unit	Range	Description
S_i_SensorResistance	SAFEDINT	mΩ	>0	NTC sensor resistance
S_i_ResistanceAt25degC	SAFEUDINT	mΩ	-	Sensor's typical resistance value at 25°C.
S_i_Beta	SAFEUDINT	K	-	NTC sensor specific beta constant

Output

Data type	Unit	Range	Description
SAFEDINT	°C	-	Measured sensor temperature.

Return value is 150 °C if any of input parameters are zero or below zero.

Example code

This example contains the validation of 2 NTC (connected to TI input pin) sensors resistance signals, conversion from resistance to temperature and the diagnostic of temperature value .

Safe definitions:

PROGRAM S_TemperatureNTC
VAR_INPUT
   S_i_SafetySystemEnable: SAFEBOOL := FALSE;
   i_NTC_A_Resistance:SAFEDINT := DINT#0;                       (*NTC A sensor resistance signal mOhm*)
   i_NTC_B_Resistance:SAFEDINT := DINT#0; (*NTC B sensor resistance signal mOhm*)
   i_NTC_A_Status: EPEC_SC.Status; (*NTC A sensor resistance signal status*)
   i_NTC_B_Status: EPEC_SC.Status; (*NTC B sensor resistance signal status*)
   i_pEventCodeNTC_A: POINTER TO EPEC_DITF.EventCode := DWORD#0;
   i_pEventCodeNTC_B: POINTER TO EPEC_DITF.EventCode := DWORD#0;
END_VAR
VAR_OUTPUT
   o_S_Temperature: SAFEDINT;
   o_TemperatureStatus:EPEC_SDV.Status;
END_VAR
VAR
   initDone: BOOL;
   validationEnable: BOOL;
   S_ValidatedResistance:SAFEDINT;
   S_Temperature: SAFEDINT;
   resistance_status: EPEC_SDV.Status;
   S_NTCValidation: EPEC_SDV.S_ValidateAI;
   S_NTCDiagnostics: EPEC_SDV.S_ValueDiagnostic;
END_VAR
VAR CONSTANT
   S_AI_TOLERANCE: SAFEDINT := DINT#100;
   S_NTC_RES_AT_25C: SAFEUDINT := UDINT#10000;
   S_NTC_Beta: SAFEUDINT := UDINT#3988;
END_VAR

Init at safe PRG:

IF NOT initDone THEN

   initDone := TRUE;

   S_NTCValidation.Init(
       S_i_InvertedCh2 := FALSE,
       S_i_DiagnosticDelay := 500,
       S_i_SafeOutputValue := DINT#0,
       S_i_Tolerance := S_AI_TOLERANCE,
       S_i_SumValue := DINT#0,
       i_pEventCode := i_pEventCodeNTC_A,
       i_pEventCodeCh2 := i_pEventCodeNTC_B
   );

   S_NTCDiagnostics.Init(
       S_i_HighErrorLimit := DINT#100,
       S_i_LowErrorLimit := DINT#-5,
       S_i_EnableHighError := TRUE,
       S_i_EnableLowError := TRUE,
       S_i_DiagnosticDelay := UINT#1000,
       S_i_SafeOutputValue := DINT#0,
       i_pEventCode := i_pEventCodeNTC_A
   );

END_IF

Code at safe PRG: