From 5f21b925dad3a99819402bb294cef9182c956c45 Mon Sep 17 00:00:00 2001
From: synco <synco.reynders@gmail.com>
Date: Mon, 20 Sep 2021 19:12:50 +1200
Subject: [PATCH] Calculating the AC only component of the samples (#1906)

Co-authored-by: Synco Reynders <synco@deviceware.co.nz>
Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>
---
 .../components/ct_clamp/ct_clamp_sensor.cpp   | 46 ++++---------------
 esphome/components/ct_clamp/ct_clamp_sensor.h | 15 +++---
 2 files changed, 18 insertions(+), 43 deletions(-)

diff --git a/esphome/components/ct_clamp/ct_clamp_sensor.cpp b/esphome/components/ct_clamp/ct_clamp_sensor.cpp
index c27134d6ac..130cdfefba 100644
--- a/esphome/components/ct_clamp/ct_clamp_sensor.cpp
+++ b/esphome/components/ct_clamp/ct_clamp_sensor.cpp
@@ -8,18 +8,6 @@ namespace ct_clamp {
 
 static const char *const TAG = "ct_clamp";
 
-void CTClampSensor::setup() {
-  this->is_calibrating_offset_ = true;
-  this->high_freq_.start();
-  this->set_timeout("calibrate_offset", this->sample_duration_, [this]() {
-    this->high_freq_.stop();
-    this->is_calibrating_offset_ = false;
-    if (this->num_samples_ != 0) {
-      this->offset_ = this->sample_sum_ / this->num_samples_;
-    }
-  });
-}
-
 void CTClampSensor::dump_config() {
   LOG_SENSOR("", "CT Clamp Sensor", this);
   ESP_LOGCONFIG(TAG, "  Sample Duration: %.2fs", this->sample_duration_ / 1e3f);
@@ -27,9 +15,6 @@ void CTClampSensor::dump_config() {
 }
 
 void CTClampSensor::update() {
-  if (this->is_calibrating_offset_)
-    return;
-
   // Update only starts the sampling phase, in loop() the actual sampling is happening.
 
   // Request a high loop() execution interval during sampling phase.
@@ -46,20 +31,23 @@ void CTClampSensor::update() {
       return;
     }
 
-    float raw = this->sample_sum_ / this->num_samples_;
-    float irms = std::sqrt(raw);
-    ESP_LOGD(TAG, "'%s' - Raw Value: %.2fA", this->name_.c_str(), irms);
-    this->publish_state(irms);
+    float dc = this->sample_sum_ / this->num_samples_;
+    float var = (this->sample_squared_sum_ / this->num_samples_) - dc * dc;
+    float ac = std::sqrt(var);
+    ESP_LOGD(TAG, "'%s' - Got %d samples", this->name_.c_str(), this->num_samples_);
+    ESP_LOGD(TAG, "'%s' - Raw AC Value: %.3fA", this->name_.c_str(), ac);
+    this->publish_state(ac);
   });
 
   // Set sampling values
   this->is_sampling_ = true;
   this->num_samples_ = 0;
   this->sample_sum_ = 0.0f;
+  this->sample_squared_sum_ = 0.0f;
 }
 
 void CTClampSensor::loop() {
-  if (!this->is_sampling_ && !this->is_calibrating_offset_)
+  if (!this->is_sampling_)
     return;
 
   // Perform a single sample
@@ -67,22 +55,8 @@ void CTClampSensor::loop() {
   if (isnan(value))
     return;
 
-  if (this->is_calibrating_offset_) {
-    this->sample_sum_ += value;
-    this->num_samples_++;
-    return;
-  }
-
-  // Adjust DC offset via low pass filter (exponential moving average)
-  const float alpha = 0.001f;
-  this->offset_ = this->offset_ * (1 - alpha) + value * alpha;
-
-  // Filtered value centered around the mid-point (0V)
-  float filtered = value - this->offset_;
-
-  // IRMS is sqrt(∑v_i²)
-  float sq = filtered * filtered;
-  this->sample_sum_ += sq;
+  this->sample_sum_ += value;
+  this->sample_squared_sum_ += value * value;
   this->num_samples_++;
 }
 
diff --git a/esphome/components/ct_clamp/ct_clamp_sensor.h b/esphome/components/ct_clamp/ct_clamp_sensor.h
index c709f6718b..2f201c11a0 100644
--- a/esphome/components/ct_clamp/ct_clamp_sensor.h
+++ b/esphome/components/ct_clamp/ct_clamp_sensor.h
@@ -10,7 +10,6 @@ namespace ct_clamp {
 
 class CTClampSensor : public sensor::Sensor, public PollingComponent {
  public:
-  void setup() override;
   void update() override;
   void loop() override;
   void dump_config() override;
@@ -35,17 +34,19 @@ class CTClampSensor : public sensor::Sensor, public PollingComponent {
    *
    * Diagram: https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/interface-with-arduino
    *
-   * This is automatically calculated with an exponential moving average/digital low pass filter.
-   *
-   * 0.5 is a good initial approximation to start with for most ESP8266 setups.
+   * The current clamp only measures AC, so any DC component is an unwanted artifact from the
+   * sampling circuit. The AC component is essentially the same as the calculating the Standard-Deviation,
+   * which can be done by cumulating 3 values per sample:
+   *   1) Number of samples
+   *   2) Sum of samples
+   *   3) Sum of sample squared
+   * https://en.wikipedia.org/wiki/Root_mean_square
    */
-  float offset_ = 0.5f;
 
   float sample_sum_ = 0.0f;
+  float sample_squared_sum_ = 0.0f;
   uint32_t num_samples_ = 0;
   bool is_sampling_ = false;
-  /// Calibrate offset value once at boot
-  bool is_calibrating_offset_ = false;
 };
 
 }  // namespace ct_clamp