Introduction: Testing a 4-20mA Pressure Transducer With the Norvi-IIOT-AE02-I Industrial ESP32 Controller

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About: ESP32 & STM32 based Industrial Controllers

A pressure transducer is a device that can sense the pressure signal and convert it into a usable output electrical signal. A process control signal that is widely used in many industries is the 4-20 mA current loop. This is an ideal method for transmitting process information about systems as the current does not change when it passes from the transmitter to the receiver.

A few of the applications of this 4-20 mA pressure transducer are,

  • Water Management
  • Pneumatics Industrial
  • OEM Equipment
  • Sub Sea Pressure
  • HVAC/R Equipment
  • Control Panels
  • Hydraulic Systems
  • Data Loggers

In this instructable, we’ll be looking at how to connect such a two wires pressure transducer with the Norvi-IIOT-AE02-I device. This device is an ESP32 embedded commercial controller which is capable of measuring 4-20 mA industrial level current.

The features of Norvi-IIOT-AE02-I are,

  • 8 Digital Inputs 24V
  • 6 Analog inputs (4-20mA)
  • 2 Transistor outputs, PWM compatible (36VDC max with 360mW collector power dissipation)
  • RS-485 Communication
  • WIFI & Bluetooth
  • Built-in OLED Display with 3 buttons
  • Expansion port with I2C, UART and GPIO

To understand the working of Norvi-IIOT-AE02-I check the instructable - Norvi-IIOT-AE02-I Device - an Industrial ESP32 Controller for (4-20mA) Current Measurement.

Check out more about the product - Norvi-IIOT-AE02-I

So what do you need to get started?

  • The Norvi IIOT-AE02-I Device
  • USB cable(Type A to Type B mini)
  • PC/Laptop
  • 4-20 mA ,12-36VDC pressure transducer
  • Wires
  • Power supply, 24V DC

Step 1: Understanding More About the Display

  • The device has a built-in 0.96 OLED SSD1306 display of 128 x 64 resolution. Its address is 03xC.
  • The GPIOs 16(SDA) and 17(SCL)of Esp32 in the device are used for I2C communication with this display.

Step 2: Understanding More About the Analog Inputs.

  • The device has two ADS1115 modules of addresses 0x48 & 0x49 respectively.
  • ADS1115 is a 16-bit analog to digital converter (ADC) that consists of four analog channels. Here in the device, the entire 4 channels of the first ADS1115 module and the first two channels of the next module are used as analog inputs.
  • The same GPIOs, 16(SDA) and 17(SCL) of Esp32 in the device are used for I2C communication with the ADCs.
  • Each ADC module is capable of measuring a maximum voltage of 4.0V. So considering this into account and to achieve a measurement of 4-20mA the above arrangement is made inside the device using an amplifier and resistor.
  • Hence it is to be noted that the value read by the analog channels of the ADC is 20 times smaller than the actual analog input reading at the analog input pins A0-A5.
  • Here for measurement of 40mV (V1) at the analog input, the current value of 4mA gets mapped(40mV/10Ω). This value gets 20 times multiplied by an amplifier and read as 800mV at the analog channel of the ADC modules. Hence the measurement of 4mA is ensured.
  • Similarly, the measurement of 20mA is achieved.

Step 3: GPIO Pins of Digital Inputs

  • GPIO pins detail of Digital Inputs are as follows,
I.0 = 18    I.1 = 39   I.2 = 34    I.3 = 35
I.4 = 19    I.5 = 21   I.6 = 22    I.7 = 23
  • Here the digital inputs are normally kept on/high (digital logic state "1") by using pull-up resistors inside the device.So when the connection is made the state changes to off/low(digital logic state "0")

To know more about how to work with the digital input side check this instructable - Getting started with Norvi Device

Step 4: Analog Inputs and GPIO Pins of Transistor Outputs

  • There are 6 analog input pins starting from A0-A5 which are capable of measuring 0-10V industrial level voltages. The first four inputs(A0-A3) are connected to the four channels of the first ADS1115 module of address 0x48 and the final two inputs (A5 & A6) are connected to the first two channels of the second ADS1115 module.
  • The GPIO pins of the transistors are as follows,
T.0 = 26   T.1 = 27

Step 5: Programming the Device

  • Install the Adafruit SSD1306, Adafruit GFX and Adafruit ADS1015 libraries in your Arduino IDE and upload the below sketch.(For installing ESP32 board and booting up the device, check steps 1 and 2 of our previous instructable - Getting Started With Norvi Devices
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_ADS1015.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1); // Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)

Adafruit_ADS1115 ads1(0x48);
Adafruit_ADS1115 ads2(0x49);

float Voltage = 0.0;
void setup()
{
  Wire.begin(16, 17);
  Serial.begin(115200);
  ads1.begin();
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C); //starting the display
  display.display();
  delay(2000);
  display.clearDisplay();
}

void loop()
{
  float adc1;

  adc1 = ads1.readADC_SingleEnded(1);
  Voltage = (adc1 * 0.1875) ;

  Serial.print("AIN0: ");
  Serial.print(adc1);
  Serial.print("\tVoltage: ");
  Serial.println(Voltage /20, 3);
  Serial.print("\tCurrent: ");
  Serial.println(Voltage /200, 3);
  delay(1000);
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(15, 0);
  display.println("Voltage Value");
  display.setCursor(45, 15);
  display.println(Voltage/20,3);
  display.setCursor(15, 30);
  display.println("Current Value");
  display.setCursor(45, 45);
  display.println(Voltage/200,3);
  display.display();
  delay(1000);
  display.clearDisplay();

}

Step 6: Understanding the Code

The necessary libraries are imported to use I2C (Wire library), to write the display (Adafruit_SSD1306 and Adafruit_GFX libraries) and to read the analog value by the ADCs. (Adafruit_ADS1015 library.)

#include <Wire.h>
#include <SPI.h>
#include <Adafruit_ADS1015.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

  • Then, the width and height of our OLED display are defined.

#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

  • Next, with the I2C communication protocol (&Wire), a display object with the width and height defined earlier is initialized.

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1); // Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)<br>

  • The below lines define the addresses of the ADCs.

Adafruit_ADS1115 ads1(0x48);
Adafruit_ADS1115 ads2(0x49);

  • A float variable is defined to store the voltage value.

float Voltage = 0.0;

  • Next, in setup(), we initialize the Serial Monitor at a baud rate of 115200.

Serial.begin(115200);

  • In the following line, you initialize I2C by setting the sda and scl GPIOs to communicate with the display.

Wire.begin(16,17);

  • Then the first ADS1115 module is initialized to begin its operation.

 ads1.begin();

  • Next, the display is initialized using its address.

display.begin(SSD1306_SWITCHCAPVCC,0x3C);

  • Using the below lines, we can ensure whether our display is working correctly. Here the display check is done for 1s (1000ms) and this can be varied.

display.display();
delay(1000);
display.clearDisplay();

  • Inside the loop() function , the float variable adc0 is initialized which is used to store output of the analog channel of the first ADC module ads1.

float adc0;

  • The below function reads the first analog channel value of the first ADC module ads1 and stores this value in “adc0” float variable.

   adc0 = ads1.readADC_SingleEnded(0);

  • This statement converts ADC value into voltage where 0.1875mV is the resolution of ADS1115.

Voltage = (adc1 * 0.1875) ;

  • The below lines prints the value of ADC, voltage read at the analog input of the Norvi device, and current on the serial monitor with a delay of one second after every reading.

Serial.print("AIN0: ");
Serial.print(adc1);
Serial.print("\tVoltage: ");
Serial.println(Voltage /20, 3);
Serial.print("\tCurrent: ");
Serial.println(Voltage /200, 3);
delay(1000);

  • The text size, text color and text position are defined. The voltage & the current values read are displayed on the OLED screen.

 display.setTextSize(1);
 display.setTextColor(WHITE);
 display.setCursor(15, 0);
 display.println("Voltage Value");
 display.setCursor(45, 15);
 display.println(Voltage/20,3);
 display.setCursor(15, 30);
 display.println("Current Value");
 display.setCursor(45, 45);
 display.println(Voltage/200,3);
 display.display();
 delay(1000);
 display.clearDisplay();

Step 7: Circuit Connection and Verification

  • Make the above circuit connection and upload the code to measure the current (control signal) sensed by the pressure transducer for your required application. (Water management, Pneumatic, etc).
  • The current value sensed by the transducer will get displayed on the device screen.

Check more about the Norvi lineup - www.norvi.lk