Claims:1. We define IoT concepts and their application in industry.
2. We choose, through comparative tests, the most suitable micro controlled platform to work with data acquisition, involving IoT.
3. We define platforms to store data on servers in the cloud.
4. We perform communication between all hardware and software: data acquisition modules, microcontroller, internet, storage platforms, web and smartphone application.
, Description:The present invention relates to evaluate and design a low-cost data acquisition system for monitoring current, voltage and temperature of the three-phase induction motor, applying IoT.
BACKGROUND OF THE INVENTION
IoT can be defined as the connection between the physical and digital world. Such technology allows everyday objects, personal or industrial, to be activated over the Internet, as long as they are equipped with embedded computing and identified, exchanging data among themselves and also with people through the network, allowing the creation of services in several areas, such as: energy, safety, environment, traffic, mobility, logistics, industry, etc.
The IoT has several applications that are having a direct impact on the consumer, such as in the health area, in the urban and rural sector. In addition to these applications, there is today a great potential for gain through the application of IoT in operational efficiency and in the increase of productive potential.
Previous works, have already demonstrated the importance of methods of monitoring in real time the operating conditions of three-phase induction motors, such as current and voltage, and performing wireless communication.
The choice of the Three-Phase Induction Motor, to be monitored by the proposed acquisition system, was due to its leadership position compared to other types of motors. Three-Phase Induction Motor is present in the most diverse sectors, particularly in industry; this leadership is maintained today and should last for a long time. In addition, induction machines are constructively robust, have high performance and low initial cost.
Low-cost acquisition systems based on microcontrollers, such as the one proposed in this work, have been researched in recent years. The use of microcontrolled platforms is a solution to acquire data from sensors, communicate with other devices, store information locally or in the cloud and alert the user when failures are detected.
A microcontroller is an IC (Integrated Circuit) capable of performing logic processes quickly, as it encompasses microprocessor circuits, memory, analog-to-digital conversion (AD) and digital input and output ports, as well as PWM (Pulse Width Modulation) circuits. - Pulse Width Modulation) and dedicated communications. The ease of programming, allied to the amount of internal circuitry, allows its use in a wide range of tasks.
Among the various microcontrollers found, three stand out for comparison purposes, as they have integrated WiFi, which are: ESP8266, ESP32 and MKR1000.
Knowledge and familiarity with these technologies become of paramount importance, as well as the study and comparison between new microcontrolled platforms that appear every day, aiming to follow the trends of industry 4.0.
ESP32 is its improved version of ESP8266, as in addition to WiFi communication, it also has Bluetooth communication.
MKR1000 is a platform designed by the Arduino group, which started its projects in the city of Ivrea, Italy, in 2005. This open-source (Open Source) electronics prototyping platform combines the functionality of previous models, in addition to having built-in WiFi. It is based on flexible and easy-to-use hardware and software, even by people who are not experts in this area.
The two aforementioned Espressif Systems microcontrollers are embedded in a NodeMCU platform, consisting of a development kit to assist in the creation of open source IoT product prototypes. For programming the MKR100, ESP32 and ESP8266 platforms, the Arduino Integrated Development Environment (IDE -Integrated Development Environment), which is open source, developed in Java, and designed to facilitate writing programs and uploading them to development platforms. This software, in addition to being used to program any Arduino platform, can also be used to develop codes for the ESP32 or ESP8266 platforms, for this reason it was used in this work.
SUMMARY OF THE PRESENT INVENTION
In this work, a current, voltage and temperature acquisition and monitoring system was presented and developed in a three-phase induction motor, applying IoT technology, designed to be a low-cost system.
The ESP32 microcontrolled platform, used in this work, proved to be efficient and fulfilled what was assigned to it, such as acquiring data, executing the code, processing and transmitting over the internet using WiFi. created some conflicts when the tests were done using only one ESP32 to run all the code, and that these conflicts were resolved when two ESP32s were used and the code was divided between them, with the first ESP32 being responsible for the acquisition and initial calculations, and the second ESP32 for application of alarm conditions and data transmission to the internet. The Voltage and Current Signals Acquisition and Conditioning Module also proved to be effective for its purpose, which was to condition the current and voltage signals to the ESP32. However, it was necessary to install an auxiliary circuit with an RC filter, to better handling of signal levels.
The WEG didactic bench served the purpose of the work very well, as it is composed of a three-phase induction motor and devices such as frequency inverter, load adjustment through the eddy brake and internal temperature sensor to the motor, which - litam simulate overvoltage, overcurrent and high temperature. Noting that the bench has a PWM inverter (not sinusoidal) and, therefore, an additional RC filter was used as a solution for monitoring.
Platforms for storing data in the cloud also served their purpose: ThingSpeak to record and make available, in graphic form, the measured values of voltage and current, as well as overvoltage, overcurrent and high temperature alarms; and Telegram to send alerts to smartphones of registered users, informing them when an overcurrent, overvoltage or high temperature event occurs. Telegram served very well, proving to be an excellent platform, providing options to create “bots” according to the application needed for the work. Safe, practical platform available for many operating systems, in addition to being open source. ThingSpeak is also an excellent platform; however it has some limitations in its free version, such as the number of channels which is limited to four and the event logging which is limited to a minimum interval of fifteen seconds.
It is concluded that the application of the internet of things in the monitoring of current, voltage and temperature in a three-phase induction motor, using low-cost acquisition systems, composed of accessible hardware and open source software, proved to be effective in its purpose. In this way, it is possible to consider that there is potential in this work, and that it can be improved in order to become a commercial product to serve small companies, for example.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
FIG 1 shows the (a) Vref Trimpot (b) Voltage Trimpot (c) Current Trimpot
FIG 2 shows the LA55P Sensor
FIG 3 shows the Simulation with potentiometers.
FIG 4 shows the Calibration curve from 0.11 to 3.36 V.
FIG 5 shows the Calibration curve from 0.11 to 2.75 V.
FIG 6 shows the Calibration curve after adjustment.
FIG 7 shows the Waveform from 0.065 mV to 1.065 mV.
FIG 8 shows the Serial Communication 2 between ESP32
FIG 9shows the Overcurrent Record, in ThingSpeak.
FIG 10 shows the Rotation reading with rated current and voltage of 242V.
FIG 11 shows the Overvoltage Record, in ThingSpeak.
FIG 12 shows the PTC thermistor resistance of the Weg motor.
FIG 13 shows the High Temperature Record, in ThingSpeak.
DETAILED DESCRIPTION OF THE INVENTION
Calibration And Communication
Voltage and current acquisition module
To perform the Three-Phase Induction Motor, current and voltage measurements, the Signal Acquisition Modules are used. They have a standard calibration, adding a passive circuit to adjust the voltage level and filter the signal to be acquired by the ESP32.
Module Calibration
The module must be calibrated before use, by its trimpots. One of them is for “Vref” adjustment, FIG 1(a), which is conventionally regulated at 1.5V. The other two are for adjusting the offset of the output signals, one for voltage, FIG 1(b), and the other for current, FIG 1(c). These must be calibrated to the same value as the “Vref”, without receiving any input signal.
The Hall Effect current sensor, LA55P, has a rated current of 50A. To measure smaller currents, we must use a greater number of turns on the sensor, and each turn multiplies the value of the current read by the module by two.
In the case of this work, three turns were used (50/3 = 16.67 ARMS), so we were able to read currents up to 16.67 A and thus have better accuracy, as shown in FIG 2. The current and voltage outputs have a signal conditioning with a range of 0 to 3.0 V, so that the signal has a zero level in the value of 1.5 V.
Signal level and filter conditioners
With the aid of an oscilloscope, the signal at the input of the Signal Acquisition and Conditioning Module (inverter signal) was measured. The output signal of the module, represented in green in FIG 3, was also measured. From the image it is possible to observe that the module output signal needs to be filtered to obtain a shape closer to the sinusoidal one. The Signal Acquisition and Conditioning Module has an anti-aliasing filter, but this filter was designed for a different frequency range from the inverter used in this work, so this anti-aliasing filter does not correctly filtered the signal, making it necessary to add an auxiliary RC (Resistive-Capacitive) filter to improve the acquisition of current and voltage signals. For the two auxiliary RC circuits (current and voltage), two trimpots of 20k ohms each were installed, associated with two ceramic capacitors of 100nF each.
With the installation of the RC filters, it was found that the signal was closer to a sine wave, without the RC filter and with the RC filter. In this FIG, the waveforms equivalent to current and voltage are the ESP32 ADC inputs, that is, after the filters. It is important to note that at this moment we did not consider the current and voltage gains, and that a load was added to the motor, which caused the current signal to be greater than the voltage signal. Another function of the trimpots was to adjust the output of the module to values from 0 to 1 V, instead of 0 to 3.0 V, which corresponds to the linear range of input voltage in the analog-to-digital converter (AD) of the ESP32.
Sampling rate
In this topic, the sampling rate used in this work was defined, which is the number of samples of an analog signal collected in a certain time interval, for conversion into a digital signal. The following formula was used to define the sampling rate:
Where: Ta = Sampling rate
T = Period = 1/f
f = frequency = 60Hz
(1)
Na = Number of samples per period = 85
The number of samples per period was determined, through tests, so that the time spent during the ESP32 interrupt service for acquiring and calculating the RMS values of current and voltage would not be too much in relation to the time available to the main program, between interrupt calls. Substituting the above values into equation (2), we find the following value for the sampling rate:
(2)
Therefore, the sampling rate is 196s.
The function that uses the sample rate, in the ESP32 code is as follows:
(3)
ESP 32
As previously mentioned, for the processing of current, voltage and temperature values, we will use ESP32, which will read the current and voltage on its analog inputs and the reading of high temperature on one of its digital inputs.
Analog Inputs
In the case of this work, as the idea is to carry out a monitoring in real time, it is important to be connected to WiFi at all times, in this way, two ESP32 were used.
Each of the ESP32 ADC inputs has 12 bits of resolution, that is, the conversion has values between 0 and 4095, corresponding to the input voltages that have default value from 0 to 3.3 V. A precaution that must be taken is that the ESP32 input pins support a maximum continuous voltage of 3.3 Volts.
Calibration curve
It was found that the variation of ESP32 is not linear, so it was necessary to carry out a calibration from the voltage variation curve by the equivalent values read in its serial. To raise the curve, two ADC inputs were used, one is simulating the current reading and the other the voltage reading, as shown in FIG 3.
With the aid of a potentiometer, different voltage levels were injected into an analog input. These were connected as follows: one of the fixed terminals was connected to the 3.3V voltage output pin, the other fixed terminal to the GND pin and the cursor (output signal) was connected to an ADC input.
At the time of the test, it was verified that, with a voltage of 110 mV, the ESP32 presented 0 in its serial, and that with a value of 3.16 V it presented 4095. The intermediate results, as well as the greater accentuation of the curve presented in the values voltage maximums are represented in the graph, as shown in FIG 4.
Another test performed was to disregard the final values to plot the graph, with this it was found that it presents a more linear curve and the R2 value is closer to the value one, as shown in FIG 5.
Adjustment of the calibration curve
Due to the non-linearity in the values close to 3.3V, it was decided to work in a range of values between 0.1 and 1.1 V. To make this possible, a function was used to read the analog input that makes it possible to reset the mitigation.
Normally, to read an analog input, pin 35, for example, the function is used:
(4)
The above function uses attenuation, in order to be able to read values in the range from 0 to 3.3V. To use zero attenuation, to perform the reading of the same pin 35, the functions:
(5)
(6)
(7)
To use the above functions, it is necessary to install the following library:
(8)
Finally, with the code ready, the tests were carried out with the potentiometer, as explained in the previous topic. The results are shown in FIG 6, with these data, the graph was generated. Note that the voltage values ranged from 0.065 to 1.065. Thus, obtaining a resolution of 1/4095.
From the general form of the 1st degree polynomial function, according to the equation below:
(9)
The value of “a” (x coefficient) and the value of “b” (constant term) were found:
𝐴 = 4108.2 and B = 275.78 (10)
These data are used in the program code, according to the equation below:
va = ((float)(leadc + 275.78))/4108.2 ; (11)
Calibration of the maximum value and rms
After adjusting the calibration curve, the code was calculated to find the maximum value, according to the equations below:
(12)
(13)
And the rms value, according to the equations below:
(14)
(15)
With the minimum (0.065 mV) and maximum (1.065 mV) voltage range found in the previous topic, a waveform was obtained, as shown in FIG 7, to feed the ESP32 analog input.
After loading the code and feeding the ESP32 analog input with a waveform signal similar to FIG 7, we find the maximum voltage and rms voltage values match the values found in FIG 7, thus proving that the code is calculating these values correctly.
Communication between ESP32 Microcontrollers
In this work, due to incompatibilities between libraries used in the program code, it was necessary to use two ESP32 microcontrolled platforms. One of the conflicts found was between the WiFi library of the ESP32 microcontrolled platform and the Interrupt Timer function, that is, the interruption does not work as expected when the ESP32 is connected to the internet. The first ESP32 is responsible for reading the data acquired by the data acquisition and conditioning module (according to a defined sampling rate), performing the calculations to find the average, maximum and rms values of voltage and current and transmitting the rms values for the second ESP32.
The second ESP32 receives the data from the first, applies a gain according to each magnitude, performs the alarm conditions for overcurrent, overvoltage and high temperature, connects to the internet, saves the results as a graph in ThingSpeak and sends alarms to the Telegram app. Some protocols were tested to carry out the communication between the ESP32, and among them it was decided to use the serial communication (TX/RX)2, because it is a simple communication and that complies with what is proposed in the work.
The simplex transmission direction was used, that is, unidirectional communication, since the first ESP32 will send the data and the second ESP32 will receive the data, not being necessary the second sends data to the first. The ESP32 microcontrolled platforms used in this work have three serials each and their respective pins are identified in Table 1.
Table 1 - Serial communication and its respective pins.
ESP32 Serial Communication
Serials TX0 RX0 TX1 RX1 TX2 RX2
Pins 1 3 10 9 17 16

ESP32 serial 2 was used to transmit data from one ESP32 to the other, thus eliminating the delay in sending data.
With this, communication between the two microcontrollers was carried out, connecting the TX pin (17) of the first ESP32 to the RX pin (16) of the second, in addition, the ground pins (GND) of the two ESP32 were also connected, as shown in FIG 8.
Thus the necessary calibrations were carried out for the current and voltage acquisition and conditioning module and the ESP32 microcontrolled platform. It was verified the importance of performing the calibration and the necessary adjustments, for a good functioning of the system. An additional RC filter to the system was also presented, in order to condition the output signal for the acquisition and calculation of rms values. Some incompatibilities and conflicts were verified, such as:
- It has been verified that some analog inputs of the ESP32 microcontroller platform stop working when the ESP32 is connected to the internet, due to a conflict between the WiFi function and the analogRead function.
- There was a conflict between the ESP32 WiFi Library and the Timer Interrupt functions.
- There was a conflict between ESP32 serial 0 and the Telegram library, as the library uses serial 0.
In order to resolve all these conflicts and incompatibilities, two ESP32 were used with different functions, where only the second one connects to the internet and the communication between the two is done by serial 2.
Experimental Results
This work presents the experimental results from the overcurrent, overvoltage and high temperature tests.
To carry out the tests, the WEG didactic bench, which has a load adjustment through a potentiometer that makes it possible to change the current, and has a CFW09 inverter that makes it possible to change the motor rotation speed and consequently the voltage value. The box designed for this work, containing the signal acquisition module and the ESP32 microcontrolled platforms, was installed on the teaching bench, for connecting the sensors to the motor.
It is important to point out that the tests were carried out using only one phase of the motor, as only one module of the three available was working correctly. However, the monitoring of only one phase was sufficient to carry out the tests necessary to obtain the results, without harming the objective of the work.
Overcurrent
For the overcurrent test, the motor was first activated via the CFW09 inverter and a sufficient time was waited for it to reach the rated speed, which according to the nameplate data is 1700 rpm. Subsequently, through the potentiometer present in the didactic workbench of Weg, the load was gradually increased and, with the aid of the ammeter clamp, the current was monitored.
The most critical condition will be used in this work, as shown below:
• Alarm when the motor current reaches a value of 1.5 rated current, ie 6.48 A (4.32 x 1.5 = 6.48 A).
When this condition is reached, a message will be sent via Telegram to the registered smartphones and the event will be registered in the ThingSpeak graph.
ThingSpeak
ThingSpeak displays the history with current reading values 9 (a), and the overcurrent alarm history, FIG 9 (b). Information on the time, day, month, year and time zone is also available. In the alarm graph, when the value is at “1” it means that the overcurrent alarm has been activated.
Overvoltage
For the overvoltage test, we based ourselves on the V/F scalar control, where varying the voltage varies the frequency and consequently the speed. This principle was used, and thus when varying the motor rotation via the CFW09 inverter, consequently the voltage also varies, and with that it was possible to simulate an overvoltage.
It was found that, for the motor to work at a constant voltage of 220 V, its rotation must be 1,410 rpm at full load, that is, a rated current of 4.32 A. The WEG teaching bench has terminals for measure voltage between phases and also terminals to measure current from a current transformer. In this way, the right multimeter shows the voltage value in volts, the CFW09 HMI that is in the center shows the rotation value in rpm and the left multimeter shows the current in amperes.
The areas with the motor work tolerance margins in relation to voltage and frequency are presented, it was found that with a voltage 10% above the nominal voltage, the motor starts to work outside the zones of tolerance.
Thus, it was considered that a voltage value 10% above 220V is considered overvoltage, that is, the motor reaching a voltage of 242V (220 x 1.10 = 242V) will trigger the overvoltage alarm.
With the help of the inverter and the multimeters, the rotation was varied up to a voltage value of 242 V, at that moment the inverter HMI indicated a rotation of 1700 rpm with current at full load, as shown in FIG 10.
Telegram
To simulate the alarm and receive the notification via Telegram, initially the motor was turned on with a rotation of 1410 rpm, after it was established, its rotation was increased to 1700 rpm, thus there was a variation in the voltage value from 220 V to 242 V, an overvoltage alarm was sent and consequently a message was sent to Telegram.
It is observed that, in addition to the overvoltage value, the Telegram message presents the engine tag, the location where it is located, the alarm time, provides an option to acknowledge the alarm and also provides a link to access the history. with voltage values and overvoltage alarms on the ThingSpeak platform page.
ThingSpeak
The graph containing the voltage values, FIG 11(a), and the graph with the history of overvoltage alarms, FIG 11(b) were made available on ThingSpeak. In the alarm graph, when the value is at “1” it means that the overvoltage alarm has been activated.
High temperature
For the High Temperature test, the PTC thermistor present in the motor windings. The PTC thermistor has a resistance of around 230 Ω at room temperature (24°C), according to measurements performed and recorded in FIG 12.
A characteristic of this thermistor is that, when the temperature rises above its breaking limit, there will be an abrupt variation in the resistance of the PTC sensor and with that it will interrupt the current in the circuit.
Based on this information, a circuit was designed to detect high temperature in the engine, with ESP32.
In a normal situation (motor in the acceptable temperature range) “0” will be set on a digital input of the ESP32, and if a temperature rise above the limit occurs, “1” will be set on the digital input and consequently an alarm will be sent via Telegram to the user informing the situation, and also the alarm will be logged in ThingSpeak.
Telegram
The message sent to the Telegram application, informs at the center of the message that the alarm was High Temperature. In addition, it also informs the engine tag, the location it is located, the alarm time, provides an option to acknowledge the alarm and also provides a link to access the history of high temperature alarms, on the ThingSpeak platform page. .
ThingSpeak
The ThingSpeak platform records and maintains a history of the times that a high temperature alarm was sent, with information on the time, day, month, year and also time zone. When the graph is at “1” it means that the alarm has been activated, and at “0” that the engine temperature is normal, as shown in FIG 13.