This experience, perhaps, is more complicated than the previous one, because it will have to make a small device. We called it chemical watchman, and more stringent his name - Gamatronic sensor. Gematronik - a new branch of science, it emerged at the intersection of electronics and chemistry. Unlike electronics, it studies the processes in liquids, where the ions move. Because the ions are much heavier than electrons, hematron processes go slower. But not always the performance is most important. Hematron devices are very reliable, they now find many applications.
Of course, these hematron devices difficult. And yet you can make a model of one such device is a sensor. First of all, it is interesting to see how hemochron. And in addition, this sensor will certainly stand you in good stead.
First, manufacture a cylindrical housing. It would be best to carve it out of plexiglass on a lathe, but not necessarily; the housing can and glue from separate plates of Plexiglas, in this case, it will be rectangular. The approximate diameter of the circular housing-40 mm and a height of about 20 mm From the ends of the cylinder it is necessary to drill two cavity depth of about 5 mm and a diameter of 30 mm, so that between them remained thick jumper. Directly under the jumper drill a horizontal hole with a diameter of 2-3 mm for filling electrolyte and pick up this hole heavy traffic. Then on the opposite side of the enclosure will be mounted one below the other three holes for electrodes with a diameter of a little more than a millimeter. The Central electrode should be in the jumper, top and bottom - in the respective cavities.
As electrodes take thick leads for collet pencils. Those places where leads you walk out of the casing, it is necessary to seal any glue. When the glue dries, the jumper will drill vertically very thin through hole with a diameter of not more than 0.5 mm . Choosing a place for him, keep in mind that this hole must pass through the middle of the stylus electrode.
The device is almost ready. Just need to stick to it on top and bottom by a thin membrane from ? e Plexiglas, only a small thickness (0.3 to 0.5 mm ). While the glue only the bottom membrane.
Now about the electrolyte. In half Cup of water dissolve 20-30 g of potassium iodide, and then slightly heated solution, add about 1 g of iodine. Through the side, the wider the hole, pour the electrolyte inside the sensor, at the bottom of the cavity, making sure not to leave air bubbles. It is easiest to perform this operation a medical syringe. When filled and the upper chamber, glue the second membrane and finally seal the body, which insert into the inlet hole prepared tube and carefully fill it with glue.
Gamatronic sensor will operate from batteries for a flashlight. The upper and lower electrodes, which is in the cavity, connect to positive terminal of the battery, the average is negative. In the circuit it is desirable to include a resistor, and voltmeter and ammeter, which, as you already know, you can replace the tester.
Using a rheostat (or resistance) check voltage of about 0.8 to 0.9 Century Microammeter in the circuit of the Central electrode will show the current 200 to 300 µa. Leave the circuit is closed 10-15 hours. The current will gradually decrease to 10-20 μa, as required. Now the sensor is ready for operation.
Check out how it works, the easiest way: blow on one of the membranes or tap the tip of the needle. At the same moment the arrow microammeter sharply deviates to the right. Eye movement membranes unnoticed, but the sensor on it immediately responded.
Explain why this is happening. The current depends on how much iodine is near the negative electrode (cathode). Under the influence of a direct current to the cathode is recovered by taking the electrons and the anode, he again formed from the ions. Therefore iodine as would be gradually transferred from the cathode to the anode. After charging the sensor current gradually decreases because of the negative electrode is less iodine. But as soon as you a little bit, even a weak touch, pushed the membrane to the cathode receives an additional, albeit very small portion of iodine molecules; the sensor instantly respond to current increases.
Such hematron devices are extremely sensitive; carefully constructed, they can sometimes respond literally to a few molecules. Their sensitivity is used in practice when the signal is weak and in other ways it is difficult to register. Such hematron device is used, for example, in medical research, in the technique for counting small parts moving on a conveyor.
Isn't there any way to use such a sensor at home or in school? Of course, you can. Why not turn it into a device that will warn you of the coming of the guest? For this purpose, the sensor enough to put in the door of the apartment, and he will respond as soon as the visitor touches the door.
But, of course, one such sensor itself for this purpose is not very convenient: it is necessary to look at the microammeter and wait until you are rejected his arrow. However, the sensor can adjust the alarm system call or an electric lamp. How to do it - think for yourself or consult with the teacher of physics.
Incidentally, this Gamatronic "watchman" can be used to protect important objects, such as banks. Of course, in this case, the sensor does not hospitable - he warns about the danger.