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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Universal programmable timer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches The timer (see figure) is designed to turn on and off from the mains (220 V) household or industrial electrical appliances for specified periods of time. Electrical appliances are connected to the output socket of the timer. The required ratio of "work" and "pause" time is set by the user using two programmers located on the top cover of the timer. One of the programmers (DD7, DD8) sets the time during which the load (Rn) is connected to the network ("work"), the other (DD5, DD6) - the period of load disconnection from the network ("pause"). The ratio of "work" and "pause" time (algorithm) can be both the same and different.
The timer can work in a cyclical mode, when the periods of "work" and "pause" replace each other as long as the timer is connected to the network. If the user needs only one cycle of changing operating modes, then the SA2 toggle switch should be switched to the right position according to the diagram. After the specified time for connecting the load to the network, the timer will no longer turn on. The initial countdown can begin with both "pause" and "work". So, for example, if it is necessary that the load be connected to the network only a few hours after the timer is turned on, then the SA3 toggle switch should be moved to the right position according to the diagram. Each of the programmers can be configured to count the following time intervals: 20,48 s; 40,96 s; 1,37 min, 2,73 min; 5,46 min; 10,92 min; 21,65 min; 43,69 min; 1,46 h; 2,91 h; 5,83 h; 11,65 h; 23,3 h; 46,6 hours (1,94 days): 93,2 hours (3,88 days). By setting the engines SA4 and SA5 in a certain way, you can set one or another ratio of the "work" and "pause" time of the timer. Each time the timer is connected to the mains, the countdown starts from the beginning (from zero). The same will happen if you press the "Reset" button (SA1) while the timer is running. Connecting and disconnecting the load from the network is carried out using a thyristor VS2. The inclusion of capacitors C6, C7 in parallel with the thyristor makes it possible to use devices containing a significant inductive component (transformers, electric motors, etc.) as a load. The included capacitors normalize the operation of the thyristor, due to which a strictly sinusoidal voltage is generated on the load without distortion and interference. In the event of an emergency shutdown of the mains voltage, it is possible to back up the power supply to the "memory" of the timer counters. To do this, a Krona-type battery or a similar rechargeable battery is connected to the socket-connector (X1, X2) located on the top cover of the device. If the mains voltage disappears and then resumes, then the timer starts counting the time not from zero, but from the moment when the mains voltage was turned off. This is especially true when counting long time delays. In this case, the programmed timer operation time is shifted only by a time equal to the time of the absence of mains voltage. The battery is installed immediately after the timer is connected to the mains (at the same time it is constantly recharged with a meager current) and removed after it is disconnected from the mains in order to avoid discharge. LED HL1 green indicates the inclusion of the timer in the network. The HL2 red LED indicates that the timer is in the "work" mode. In the absence of the HL2 LED, the timer is in the "pause" mode. The power supply of the timer is transformerless, half-wave with quenching capacitors C1, C2 [1]. The output voltage of the power supply is 9,8 V. If the SA2 toggle switch is set to the "cyclic" mode, and the SA3 toggle switch is set to the "from work" mode, then after the timer is turned on, the DD1.3 input is set to a low logic level, and the output is high. The DA3 switch, switched on by the SA1.3 toggle switch, transmits a high level through the VD16 diode to the input of the generator assembled on the elements DD3.3 and DD3.4. The generator generates unlocking pulses, which are fed through the paired buffer elements DD4 and capacitor C8 to the base of the transistor VT1, which controls the operation of the pulse transformer T1 and the thyristor VS2. Thus, the load at this stage is connected to the network. At the same time, the mains voltage rectified by the VD1 diode through the quenching resistor R2 is fed to the input 6 DD1.2 of the Schmitt trigger. The trigger is triggered by each half-wave of the rectified mains voltage, generating 4 rectangular pulses with a frequency of 50 Hz at its output. These pulses are fed to the counting input 10 of the counter DD7 [2]. Now the time during which the load will be connected to the network depends on the position of the SA5 contact slider. The high logic level received from one of the outputs of the counters DD7, DD8, through the diode VD15 will go to the input 12 of the trigger DD2.2. At its output 14 and at the input DD1.3 will be a high level, and the load will be disconnected from the network. The feedback chain R23 and VD12 "latches" the trigger in this state. Now, a high logic level through the resistor R18 and the switch DA3 opened by the toggle switch SA1.1 is transmitted to the control input 12 of the switch DA1.2, allowing the passage of counting pulses through the resistor R12 to the counting input 10 of the counter DD5. From this moment, the countdown of the "pause" time begins, during which the load will be disconnected from the network. As soon as one of the outputs of the counters DD5, DD6, connected to the SA4 contact engine, a high-level pulse appears, all counters on the R inputs will be reset. The same pulse generates a low logic level at the output 4 of the DD3.2 element, due to which the high level on the DD2.2 latch is “reset” through the VD17 diode to pin 4 of DD3.2. At the input of element DD1.3, a low logic level is again set, and the load Rn is again connected to the network. Then the process is repeated. When the SA3 toggle switch is set to start work "with a pause", a chain of elements DA1.4, DD1.4, DD3.1 comes into effect. The DA1.3 switch is turned off by the SA3 toggle switch, and the DA1.4 switch, on the contrary, is turned on. After the timer is connected to the network, the output 14 of the DD2.2 trigger is low. At the output 3 of the element DD3.1 - also a low level, and the load Rn is disconnected from the network. Here, on the contrary, the "pause" time is counted by the counters DD7, DD8, and the "work" time is counted by the counters DD5, DD6 (which should not be forgotten when programming). After the "pause" time countdown, the low level on the DD2.2 trigger will change to a high one. The logic level at output 3 DD3.1 will also become high, and the load will be connected to the network. At the same time, a high level from output 3 DD3.1 through the diode VD13 will go to the control input 13 of the switch DA1.1. The switch will allow high-level broadcasting from the DD2.2 latch to the control input 12 of the DA1.2 switch, which will pass counting pulses from the DD1.2 element to the counting input From counter DD5. The countdown of the "work" time will begin, after which the high level received by the SA4 engine will reset all counters to zero at the R inputs, and the DD3.2 element will reset the DD2.2 latch to a low level. In this case, if the SA2 toggle switch is in the "single" position, then the same high logic level, received through the VD11 diode, will "latch" on the DD2.1 trigger and, bypassing the VD9 diode, will be constantly present at the reset inputs R of all four counters, blocking their operation. And while the timer is connected to the network or the backup battery GB1 is installed, the load Rн will no longer be connected to the network. And if the SA2 toggle switch is set to the "cyclic" position, then the process of changing the "pause" and "work" phases will continue. As the core of the pulse transformer T1, a piece of ferrite was used, about 20 ... 25 mm long and 8 mm in diameter (from the ferrite core of the magnetic antenna of the radio receiver). The primary winding contains 100 turns of winding wire PEV-2 with a diameter of 0,2 ... 0,3 mm, the secondary winding - 40 turns of the same wire Thyristor VS2 and rectifier bridge diodes VD19-VD22 should be installed on radiators, the area of which depends on the expected power of the connected load Rn. Based on the same considerations, you should choose the type of thyristor VS2 and rectifier bridge diodes. The chain C9, R26, C10 prevents interference from the operation of the thyristor from entering the network. Due to the fact that contact X2 of the backup power supply is located outside the device and is not galvanically isolated from the network, for the purposes of electrical safety, special attention should be paid to protective elements - resistor R19 and diode VD6. The maximum allowable reverse voltage of the diode must be at least 500 V, and the resistance of the resistor R19 must be at least 30 kOhm with a maximum dissipation power of 0,5 ... 1 W. As programmers, you can use small-sized multi-contact switches or use removable jumpers between the contacts SA4, SA5 and the output buses of the meters. To eliminate the influence of parasitic capacitances and inductances, it should be remembered that the signal tracks on the board should be as small as possible in length and width, and it is better to make the tracks of the microcircuit power buses wider. The shape of the counting pulses in all sections of their repetition should be rectangular with a steep front and a cutoff, which should be checked using an oscilloscope. If any distortion of the pulse shape is detected, then this section should be connected to the common bus of the device through a resistor with a resistance of about 150 kOhm. It should be noted that the "single" mode can be applied only when the SA3 toggle switch is set to the "from pause" position. However, if the initial cycle "from work" is necessary, this disadvantage is practically eliminated if the duration of the pause is made minimal, i.e. 20,5 s After this short period of time, the load will be connected to the network for a specified period, after which it will no longer be turned on. References:
Author: O.R. Kondratiev
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