ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Thermometer for gas water heater. Encyclopedia of radio electronics and electrical engineering Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers The use of a gas water heater (column) installed in some apartments is often associated with inconvenience. If, for example, the column is located in the kitchen, then to check and adjust the temperature of the water filling the bath, you have to repeatedly go from the bathroom to the kitchen and back. It is advisable to install a water temperature sensor at the place of its consumption, and an indicator next to the column. In this case, you can adjust the temperature without leaving the column. An electronic thermometer, the circuit of which is shown in fig. 1 solves this problem. The temperature sensor is three semiconductor diodes connected in series (VD1-VD3). They can be of any type - germanium or silicon. It is only important that the diodes are small-sized, this will reduce the inertia of the device. A stabilized supply voltage of 5 V is supplied from any suitable source. The consumed current does not exceed 10 mA. I used the BP2-3 power supply from the BZ-34 calculator kit. The operation of the thermometer is based on the fact that the voltage drop across a semiconductor diode at a constant forward current depends linearly on the temperature of its pn junction. If, at zero temperature, the engine of the tuning resistor R5 is set in such a way that the voltage between it and the minus of the power source is equal to the voltage drop across the diodes VD1-VD3, there is no current through the PA1 microammeter under these conditions. With the heating of the diodes, the voltage across them decreases and a current proportional to the temperature will flow through the microammeter. The frame of the microammeter used by the author with the resistance Rp=617 Ohm is made of copper wire (temperature coefficient of resistance α=4,3-10-3 °C-1). When the temperature of the frame changes by ΔТ=20 °С, the increase in its resistance will be Since the dynamic resistance of the diodes VD1-VD3 is small and the values of the resistors R4-R6 are small, the current flowing through the RA1 microammeter at a given temperature depends mainly on the sum of the resistances R2, R3 and Rp. In this case, it is approximately equal to 7 kOhm. Having made the proportion 7000 Ohm - 100%, 53 Ohm - x%, we find Consequently, with temperature fluctuations at the installation site of the RA1 microammeter by 20 ° C, the thermometer readings will change by less than 1%. But if you leave one diode in the circuit, in order to maintain the same sensitivity of the device, you will have to reduce the total resistance of the resistors and the frame by three times, so the error will triple. The thermometer is calibrated in the following sequence:
It remains to fix the diodes on the pipe through which hot water flows, as close as possible to the place where you want to control its temperature. A possible mounting option is shown in Fig. 2. So that the temperature of diodes 2 does not differ from the temperature of pipe 1 and the water in it, the assembly should be covered with asbestos thermal insulation 3, and on top of it - with aluminum foil 4. With wires 5, the length of which is practically unlimited, diodes 2 are connected to the rest of the thermometer elements, which can be placed near the regulator of the geyser, even located in another room. Author: V.Burkov, Ivanovo See other articles Section Power regulators, thermometers, heat stabilizers. Read and write useful comments on this article. Latest news of science and technology, new electronics: Machine for thinning flowers in gardens
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