To maintain the temperature of the air in the room, in the balcony box food storage, water in the tank will fit the thermostat, the description of which below. It has high accuracy, long term stability and can control a comparatively powerful heater.
Diagram of the device shown in Fig. 1.
(click to enlarge)
Temperature sensor B1 - a specialized chip AD22100KT, the output the voltage which is almost linearly dependent on the ambient temperature. To calculate the value of the voltage U in volts at a temperature T, given in degrees Celsius, according to the formula
where Fe is the supply voltage of the sensor, V.
On a chip of DA2 assembled voltage comparator. The sensor signal is fed to it the entrance is through a filter R1C3 suppressing interference and crosstalk. As Executive element applied photothyristor U1, switching the heater via a diode bridge VD3 - VD6. Led HL2 signals filed on command of the heater.
On the step-down transformer T1 and diodes VD1, VD2 assembled rectifier, and chip DA1 stabilizer voltage sensor. Led HL1, indicating the presence of voltage at the rectifier output, signals the connection of the device to the network.
The regulator operates as follows. The inputs of the comparator receives a voltage from the output of the sensor B1 and model of engine, variable resistor R3. If the temperature is above the setpoint, the current in the control circuit photothyristors and not leaking the latter is closed. The heater is de-energized.
With decrease in temperature, the voltage at the output of the sensor will be smaller model that will result in the switching of the comparator. Photothyristor opens, closing the supply circuit of the heater. The temperature of the object increases, and the device going back to the original state in which the heater is off.
Structurally, the thermostat consists of three nodes connected by bundles of wires with the connectors. The first node of the temperature sensor B1. Specified in the diagram, the device AD22100KT operates in the temperature range 0...+100°C. For in the range -40...+85 °C need AD22100AT, and in the range of -50...+150 °C - AD22100ST. For use in a liquid medium, the sensor must be protected from direct contact with it, and its connecting wires are heavily insulated.
The second node is a printed circuit Board on which the chip installed, most of other details and the plug connectors X1 and x2. The sketch Board is shown in Fig. 2. It calculated on oxide capacitors K50-35 or similar imported and fixed resistors as indicated on the scheme of power. Wire multi trimmer resistor SP5-WB (R3) is installed outside of the Board. Fork X1, x2 series PLS. Similar can be found in the faulty computer modules. Diodes VD1, VD2 when need replace other rectifier, for example, KD105B, CDA.
The third site - the power components of the controller and the LEDs. All of them together with the circuit Board of the second node encapsulated in a body of insulating material. The bridge from diodes VD3-VD6 can be substituted with a single node, for example, SWРС1006 or SWРС1004. When the load current is more than 1.. .2 And the diode bridge and photothyristor necessary heat sinks, but if the heater power is more than 2.2 kW, these elements should be replaced with other appropriate power. The transformer T1 should provide a rectified voltage 12... 15 V At a current load 100 mA. The LEDs will fit any.
Establishing begin with installation of the boundaries of the temperature range in which plans the operation of the controller. To do this, choose the values of resistors R2 and R4. The voltage drop across the resistor R4 must be calculated on the above formula for the minimum, and the series-connected R3 and R4 for the maximum temperature interval.
The value of the resistor R6 is selected so that the control circuit U1 photothyristor there was a current of approximately 100 mA. If the switching on and off of the heater happen with the "bounce", to eliminate it by setting shown in the diagram dashed lines resistor R9. It will create a small switching hysteresis of the comparator.
Author: I. Nechaev, Kursk