Problem with SF800 flow sensor reading

I am having a problem with my flowsensor circuit as show in the figure.

where SF800 is the flow sensor I am using. It's a pulse sensor PNP/NPN contact. Hence the pulse signal pin in pull up using a 2.2 kΩ resistor as the manufacturer says. The K - Factor of the sensor given by the manufacturer is around 5600 pulses per litre. SF800 sensor is provided with a 3/8-inch NPT male threaded connection.

// Interrupt handler static void IRAM_ATTR flow_sensor_isr_handler(void* arg) { if (PULSE_TASK_FLAG) { PULSE_COUNTER++; } } void init_flow_sensor() { // Configure GPIO gpio_config_t io_conf = { .pin_bit_mask = (1ULL << GPIO_PULSE_SENSOR_IO), .mode = GPIO_MODE_INPUT, .pull_up_en = GPIO_PULLUP_ENABLE, .pull_down_en = GPIO_PULLDOWN_DISABLE, .intr_type = GPIO_INTR_NEGEDGE // Falling edge trigger }; gpio_config(&io_conf); // Install ISR service gpio_install_isr_service(ESP_INTR_FLAG_NMI); // Attach interrupt handler gpio_isr_handler_add(GPIO_PULSE_SENSOR_IO, flow_sensor_isr_handler, NULL); } static void pulse_task (void *arg) { const char * tag = "PULSE Task "; char packet[64]; // Initialize flow sensor init_flow_sensor(); // Initialize last time lastTime = esp_timer_get_time(); while (1) { // ESP_LOGI(tag, "Pulse Test"); if (PULSE_TASK_FLAG) { int64_t currentTime = esp_timer_get_time(); int64_t deltaTime = currentTime - lastTime; if (deltaTime >= 100000) { // Update every 1 second (in microseconds) uint32_t currentPULSE_COUNTER = PULSE_COUNTER; PULSE_COUNTER = 0; // Reset counter // Calculate flow rate and total flow FLOW_RATE = (currentPULSE_COUNTER / (float) K_FACTOR) * 600; // Convert pulses/sec to LPM TOTAL_FLOW += FLOW_RATE * (deltaTime / 60000000.0); // Add to total flow (convert us to minutes) // ESP_LOGI(TAG, "Delta: %lld, Flow Rate: %.2f LPM | Total Flow: %.2f L", deltaTime, FLOW_RATE, TOTAL_FLOW); lastTime = currentTime; } // Send FUEL Data to the HMI gen_packet("FUEL", "PUL", TOTAL_FLOW, packet, sizeof(packet)); // Generate packet sendData(tag, packet); vTaskDelay(pdMS_TO_TICKS(10)); if (DEF_SET_VALUE && TOTAL_FLOW >= DEF_SET_VALUE) { pump_stop(); ESP_LOGI(tag, "Set value %.2f reached! --- %.2f", DEF_SET_VALUE, TOTAL_FLOW); } } else { // Pause counting when the flag is not set // } vTaskDelay(pdMS_TO_TICKS(10)); } } 

The problem I am facing is that when I test it for 5 litres I am getting an error of (+/-)30 ml. (Say for 5 litres I get from 4.98 to 5.10 litres. Also when I go for 10 litres the error buildup is also increasing (but no linearly). Also it varies if I decrease the flow through the sensor using a valve). Hence this error is not at all acceptable. I need the error to be minimal say 20 ml max.

I am getting a doubt that there should be some mistake in my code. SF800 is said to be an accurate sensor [No Detailed Datasheet is available for the sensor other than its connection diagram]. The code is done based on ESP IDF framework. The code block containing the pulse task is attached above. The Pulse task is a FreeRTOS Task which run independantly.

The PULSE_TASK_FLAG is set high when the motor is switched ON, which causes the water to flow through the sensor. Then the task starts calculating the TOTAL_FLOW through the sensor until the motor is Switched OFF. flow_sensor_isr_handler is an interrupt handler which counts the pulses.

I would be grateful for any recommendations of alternative sensors that you have successfully implemented in previous projects.

If there is a requirement for any more information I can provide it.