Published December 25, 2021

Low Pass Filter for Thermocouple Temperature Sensor

All signals in nature contain noise components that affect the original signal. Therefore, we always try to remove noise from digital signal

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Low Pass Filter for Thermocouple Temperature Sensor

Things used in this project

Hardware components

Hexabitz 4-Pin USB-Serial Prototype Cable

Hexabitz BitzClamp

Hexabitz STLINK-V3MODS Programmer (H40Rx)

Hexabitz Thermocouple Temperature Sensor (H09R0x)

Software apps and online services

STMicroelectronics STM32CubeIDE

STMicroelectronics STM32CubeMonitor

Story

. In this project, we will apply a low pass filter to a digital signal recorded from Hexabitz temperature sensor module (H09R0).

First, we connected the STLINK(H40R0) programming module to the thermocouple temperature module (H09R0) so that the module can be programmed as shown in the following figure:

The low-pass filter is applied using the following equations:

To transform Z, we substitute all S by the following equation:

After substitution, the equation becomes a formula for Z:

The cutoff frequency was chosen based on the sampling time of the module's analog-to-digital converter, where the sampling time is 239.5 clock cycles and the cutoff frequency is therefore 0.041 HZ. The sampling frequency should be greater than the cutoff frequency, so we chose a frequency of 4 HZ.

Substituting the cutoff frequency and the sampling frequency into the previous equation gives the final form of the low-pass filter equation applied to the thermocouple temperature module signal:

The signal was monitored by the STM32CubeMonitor software.

In the figure (1) the folder reading the signal was selected by the temperature module.

Figure (1): STM32CubeMonitor configurations- selecting the right folder

Figure (2), Notice that the file extension is “.elf”.

Figure (2): STM32CubeMonitor configurations- selecting the right file

In figure (3), you can see the selection of the variable that measures the temperature, and the other variable is the filtered signal.

Figure (3): STM32CubeMonitor configurations- selecting the right variables

In the figure (4), we see the output of the module, i.e., the signal before filtering and the signal after filtering.

Figure (4): The output of the module

Low Pass Filter for Temperature Sensor

/*
 BitzOS (BOS) V0.2.5 - Copyright (C) 2017-2021 Hexabitz
 All rights reserved

 File Name     : main.c
 Description   : Main program body.
 */
/* Includes ------------------------------------------------------------------*/
#include "BOS.h"

/* Private variables ---------------------------------------------------------*/
float tempc;
float tempc1;
float lpf_temp,lpf_temp1;
/* Private function prototypes -----------------------------------------------*/

/* Main function ------------------------------------------------------------*/

int main(void){

	Module_Init();		//Initialize Module &  BitzOS

	//Don't place your code here.
	for(;;){}
}

/*-----------------------------------------------------------*/

/* User Task */
void UserTask(void *argument){

	// put your code here, to run repeatedly.
	while(1){
		//take samples from the temperature module
		SampleC(&tempc);
		//take the previous sample
		lpf_temp1=lpf_temp;
		tempc1=tempc;
		//low-pass filter equation applied to the temperature module signal
		lpf_temp1=0.9377*lpf_temp+0.031*tempc+0.03*tempc1; //fc=0.041Hz
		Delay_ms(10);


	}

	 }


/*-----------------------------------------------------------*/

Credits

Esraa Alkadour

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Low Pass Filter for Thermocouple Temperature Sensor

Things used in this project

Hardware components

Software apps and online services

Story

Code

Low Pass Filter for Temperature Sensor

Credits

Esraa Alkadour

Comments

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Low Pass Filter for Thermocouple Temperature Sensor

Low Pass Filter for Thermocouple Temperature Sensor

Things used in this project

Hardware components

Software apps and online services

Story

Code

Low Pass Filter for Temperature Sensor

Credits

Esraa Alkadour

Comments

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