The use of a homemade thermal imager based on the Arduino in the study of energy saving
What can be done with the help of two bricks, an ordinary hotplate and a thermal imager on the Arduino ? Save a bunch of electricity! How all these things are interrelated, you can learn from this article. Along the way, I had to touch on some things from TAU (automatic control theory), but I tried to get rid of boring mathematics and explain in detail the role of the “thermal imager for less than $ 100” in the process.
Attention! Under the cut there is one very “thick” but beautiful picture! And a lot of text!
Today, almost everyone in the household has electric heaters - tiles, kettles, heaters and boilers at the worst. In general, the principle of their work can be described as follows - the current flows through the nichrome filament and causes it to heat up, and the meter also takes care of it. All heaters "eat" a lot of electricity, so it was. However, there is a way out!
The fact is that any body has its own “thermal inertia”, and here it is possible to give an incompletely accurate but understandable analogy with a large round cobblestone:
')
Imagine that the cobblestone needs to be rolled back a distance of ten meters. You can immediately lean on him with all your weight, throughout the whole section you can push what forces you have and thus move it to the right place. And you can first move it, and then only slightly push. Of course, in the second case, we will tire less. So, by analogy, the first method is to turn on the heater directly into the network, and the second is to use energy-saving control algorithms.
And this means that we can apply a special-shaped voltage to the input of the electric heating element, which will allow us to achieve the desired temperature, but with less electricity (kWh). Of course, while saving is not taken from the air. And it appears due to an increase in heating time, and the longer the time, the greater the savings, respectively! How to calculate such control is a long history and in the framework of this article it will be affected only superficially (for matane).
So, take, for example, for the study of an ordinary electric stove, with a capacity of 1 kW. And we put on it two silicate bricks - to increase the very "thermal inertia" (and as you already understood, the more this conditional value is, the grander the percentage of savings). Here is this beauty:
I agree, it does not look very good! She has seen a lot in her lifetime, and nonetheless will continue to serve in the name of science and beyond.
To calculate the energy-saving control for a given electric heater, firstly, you need to complete the task of compiling its simplest mathematical model. It can be, for example, a differential equation or, as in this case, a transfer function. In the language of Wikipedia, the transfer function is a differential operator expressing the connection between the input and the output of a linear stationary system. And knowing the input signal of the system and the transfer function, you can restore the output signal.
In electric heaters, the input value is the effective value of the voltage , and the output is the temperature of the object. And having a transfer function of a thermal object in our hands, we can, by applying a voltage of 220V to the input, to obtain the temperature value at the output, which means we can own the real mathematical model.
Having opened any textbook on TAU, one can make sure that there are a great many varieties of transfer functions. So how do you know which one will most accurately describe the object of study? To do this, it is necessary to conduct a kind of "identification", according to the science - to identify the object. It sounds serious, but in practice it looks like this: turn on the network and measure the temperature during the entire heating time. Here's what happens in the case of a hotplate:
Based on the type of function, it is safe to conclude that the hot plate is accurately described by the transfer function, called aperiodic link of the second order . This is how it looks like:
Here, the input value U (t) denotes the voltage, which can be both constant in time (220V, meaning the effective value), and changing according to some law. The output value x (t) is the temperature. From the picture it can be understood that this link has its own parameters - K, T1 and T2, which are called the gain and time constants, respectively. As their names imply, the value of K reflects the magnitude of the change in the signal passing through such a link, and the time constants directly depend on the very “thermal inertia” of the object. These coefficients can be approximately calculated from the previous graph. And, obviously, they affect the accuracy of the mathematical model, and hence the amount of electricity saved.
Looking ahead, I will say - for this tile, for more than a year, students have been counting on the very energy-efficient management (which is why it is so worn). And time after time, to identify the object (well, to get that schedule from above) the thermocouple was positioned strictly in the middle between the bricks. Well, a natural question arose - what if we took and moved the temperature sensor to a completely different place, how would the parameters of the object change? Each time conducting an experiment with a different position of a thermocouple would be extremely long - as one can understand from the graph above, one experiment takes almost three hours. And here just right is the use of the same imager on the Arduino.
The main drawback of the device just mentioned is that the image acquisition time in the infrared range for a long time is almost irrelevant here — the experiment goes on for a very long time compared to the scanning time. But as a result, it turns out not one graph of temperature changes at one point, but 768 whole! In accordance with the resolution of the thermogram 32x24 pixels.
Thus, using a thermal imager, a similar experiment was performed to identify the object - 25 thermograms were taken in a few hours. The scan area covered almost the entire side surface of the bricks, as shown in the picture:
And this is how the heating process in the infrared range looks like (a kind of infrared time-lapse):
It is worth noting that the false colors in the thermogram are assigned automatically depending on the maximum and minimum measured temperature, and the matching gradient also dynamically changes.
The discovery was that the heating center was shifted to the left, although the chamber was directed strictly along the center of the bricks. This is probably due to irregularities inside the lower brick, or the design of the heating element of the tile.
The Arduino thermal imager works as follows - first a spatial temperature matrix is compiled, then a picture in a false color is already visualized on it. This turned out to be a huge plus - since the output of the system is not only a beautiful picture, but also a matrix file, which plays a major role in the study. Taking offhand five points on such matrices (there are 25), we can track the dynamics of temperature change:
This is how the graphs of transients will look like (as these dependencies of temperature on time are called) at five selected points and from a thermocouple for comparison:
The graphs from the thermal imager are more clumsy, since they are based only on 25 points, whereas data from a thermocouple is received every two seconds. In addition, the naked eye can notice the difference in temperature graphs from a thermocouple and thermal imager. Perhaps this is due to the physical difference in measurement methods - if the thermocouple is located as if “inside” the object, then the infrared sensor of the thermal imager scans the surface, which is in turn influenced by the processes of evaporation of moisture and air convection.
Further, from these graphs, you can get the very coefficients (K, T1 and T2) to create a mathematical model of the electric stove. However, this time, we will have not one, but as many as six models!
Having omitted the mathematical part, it is worth noting that in the process of the study an interesting feature was noticed - the values of the coefficients depend on the location of the point on the thermogram relative to the intended center of heating - this red area at the bottom of the thermogram. Moreover, their dependence is almost linear:
And since it is known that the graphs do not lie, focusing on the position of the measuring point in principle, it is possible to determine the coefficients for almost any point of the object, without resorting to plotting graphs for all 768 points.
Nevertheless, out of these five previously selected points, the left point showed the best results in energy saving. As part of a system with a regulator configured based on data obtained from this point:
The percentage of savings is considered compared to the energy spent on heating the stove up to 80 degrees by simply plugging it into an outlet. How to change the voltage on the electric stove to save almost 40% of electricity, you can look at this chart:
Here, the optimal control is indicated by U (t), the corresponding tile temperature with such control is T (optimal). For comparison, there are also graphs of the voltage and temperature of the tile with a simple connection to the network. As you can see, the savings are obtained by increasing the heating time by almost three times.
Summing up:
So, if the whole article tormented you the question, why do you need to heat the bricks on a tile and consider some mythical economy, if in practice nobody needs it, then you have a worthy answer: the fact is that this tile is a direct analogue of such an object of study as a stove resistance. This industrial monster with a power of 800 kW (for example) consumes not just a lot, but catastrophically a lot of electricity. And, accordingly, energy saving is very important.
The thermal imager in this case played a huge role, allowing us to build the most complete picture of the processes occurring during the operation of electric heaters, and on the basis of these data to obtain an even more accurate object from the point of view of energy saving, and moreover, to finally find serious application as a full-fledged device .
Attention! Under the cut there is one very “thick” but beautiful picture! And a lot of text!
Today, almost everyone in the household has electric heaters - tiles, kettles, heaters and boilers at the worst. In general, the principle of their work can be described as follows - the current flows through the nichrome filament and causes it to heat up, and the meter also takes care of it. All heaters "eat" a lot of electricity, so it was. However, there is a way out!
The fact is that any body has its own “thermal inertia”, and here it is possible to give an incompletely accurate but understandable analogy with a large round cobblestone:
')
Imagine that the cobblestone needs to be rolled back a distance of ten meters. You can immediately lean on him with all your weight, throughout the whole section you can push what forces you have and thus move it to the right place. And you can first move it, and then only slightly push. Of course, in the second case, we will tire less. So, by analogy, the first method is to turn on the heater directly into the network, and the second is to use energy-saving control algorithms.
And this means that we can apply a special-shaped voltage to the input of the electric heating element, which will allow us to achieve the desired temperature, but with less electricity (kWh). Of course, while saving is not taken from the air. And it appears due to an increase in heating time, and the longer the time, the greater the savings, respectively! How to calculate such control is a long history and in the framework of this article it will be affected only superficially (for matane).
So, take, for example, for the study of an ordinary electric stove, with a capacity of 1 kW. And we put on it two silicate bricks - to increase the very "thermal inertia" (and as you already understood, the more this conditional value is, the grander the percentage of savings). Here is this beauty:
I agree, it does not look very good! She has seen a lot in her lifetime, and nonetheless will continue to serve in the name of science and beyond.
To calculate the energy-saving control for a given electric heater, firstly, you need to complete the task of compiling its simplest mathematical model. It can be, for example, a differential equation or, as in this case, a transfer function. In the language of Wikipedia, the transfer function is a differential operator expressing the connection between the input and the output of a linear stationary system. And knowing the input signal of the system and the transfer function, you can restore the output signal.
In electric heaters, the input value is the effective value of the voltage , and the output is the temperature of the object. And having a transfer function of a thermal object in our hands, we can, by applying a voltage of 220V to the input, to obtain the temperature value at the output, which means we can own the real mathematical model.
Having opened any textbook on TAU, one can make sure that there are a great many varieties of transfer functions. So how do you know which one will most accurately describe the object of study? To do this, it is necessary to conduct a kind of "identification", according to the science - to identify the object. It sounds serious, but in practice it looks like this: turn on the network and measure the temperature during the entire heating time. Here's what happens in the case of a hotplate:
Based on the type of function, it is safe to conclude that the hot plate is accurately described by the transfer function, called aperiodic link of the second order . This is how it looks like:
Here, the input value U (t) denotes the voltage, which can be both constant in time (220V, meaning the effective value), and changing according to some law. The output value x (t) is the temperature. From the picture it can be understood that this link has its own parameters - K, T1 and T2, which are called the gain and time constants, respectively. As their names imply, the value of K reflects the magnitude of the change in the signal passing through such a link, and the time constants directly depend on the very “thermal inertia” of the object. These coefficients can be approximately calculated from the previous graph. And, obviously, they affect the accuracy of the mathematical model, and hence the amount of electricity saved.
Looking ahead, I will say - for this tile, for more than a year, students have been counting on the very energy-efficient management (which is why it is so worn). And time after time, to identify the object (well, to get that schedule from above) the thermocouple was positioned strictly in the middle between the bricks. Well, a natural question arose - what if we took and moved the temperature sensor to a completely different place, how would the parameters of the object change? Each time conducting an experiment with a different position of a thermocouple would be extremely long - as one can understand from the graph above, one experiment takes almost three hours. And here just right is the use of the same imager on the Arduino.
The main drawback of the device just mentioned is that the image acquisition time in the infrared range for a long time is almost irrelevant here — the experiment goes on for a very long time compared to the scanning time. But as a result, it turns out not one graph of temperature changes at one point, but 768 whole! In accordance with the resolution of the thermogram 32x24 pixels.
Thus, using a thermal imager, a similar experiment was performed to identify the object - 25 thermograms were taken in a few hours. The scan area covered almost the entire side surface of the bricks, as shown in the picture:
And this is how the heating process in the infrared range looks like (a kind of infrared time-lapse):
It is worth noting that the false colors in the thermogram are assigned automatically depending on the maximum and minimum measured temperature, and the matching gradient also dynamically changes.
The discovery was that the heating center was shifted to the left, although the chamber was directed strictly along the center of the bricks. This is probably due to irregularities inside the lower brick, or the design of the heating element of the tile.
The Arduino thermal imager works as follows - first a spatial temperature matrix is compiled, then a picture in a false color is already visualized on it. This turned out to be a huge plus - since the output of the system is not only a beautiful picture, but also a matrix file, which plays a major role in the study. Taking offhand five points on such matrices (there are 25), we can track the dynamics of temperature change:
This is how the graphs of transients will look like (as these dependencies of temperature on time are called) at five selected points and from a thermocouple for comparison:
The graphs from the thermal imager are more clumsy, since they are based only on 25 points, whereas data from a thermocouple is received every two seconds. In addition, the naked eye can notice the difference in temperature graphs from a thermocouple and thermal imager. Perhaps this is due to the physical difference in measurement methods - if the thermocouple is located as if “inside” the object, then the infrared sensor of the thermal imager scans the surface, which is in turn influenced by the processes of evaporation of moisture and air convection.
Further, from these graphs, you can get the very coefficients (K, T1 and T2) to create a mathematical model of the electric stove. However, this time, we will have not one, but as many as six models!
Having omitted the mathematical part, it is worth noting that in the process of the study an interesting feature was noticed - the values of the coefficients depend on the location of the point on the thermogram relative to the intended center of heating - this red area at the bottom of the thermogram. Moreover, their dependence is almost linear:
And since it is known that the graphs do not lie, focusing on the position of the measuring point in principle, it is possible to determine the coefficients for almost any point of the object, without resorting to plotting graphs for all 768 points.
Nevertheless, out of these five previously selected points, the left point showed the best results in energy saving. As part of a system with a regulator configured based on data obtained from this point:
The percentage of savings is considered compared to the energy spent on heating the stove up to 80 degrees by simply plugging it into an outlet. How to change the voltage on the electric stove to save almost 40% of electricity, you can look at this chart:
Here, the optimal control is indicated by U (t), the corresponding tile temperature with such control is T (optimal). For comparison, there are also graphs of the voltage and temperature of the tile with a simple connection to the network. As you can see, the savings are obtained by increasing the heating time by almost three times.
Summing up:
So, if the whole article tormented you the question, why do you need to heat the bricks on a tile and consider some mythical economy, if in practice nobody needs it, then you have a worthy answer: the fact is that this tile is a direct analogue of such an object of study as a stove resistance. This industrial monster with a power of 800 kW (for example) consumes not just a lot, but catastrophically a lot of electricity. And, accordingly, energy saving is very important.
The thermal imager in this case played a huge role, allowing us to build the most complete picture of the processes occurring during the operation of electric heaters, and on the basis of these data to obtain an even more accurate object from the point of view of energy saving, and moreover, to finally find serious application as a full-fledged device .
Source: https://habr.com/ru/post/226313/
All Articles