The purpose of this instrument is to demonstrate an application of a ring counter which drives an opto-isolated SCR. SCR in turn will s witch ON a 230V AC activated device as and when a trigger pulse from these counter is applied to the gate of this SCR through an opto-isolator module. A Lamp load is used to demonstrate this principle. This can be used as either a Straight Binary counter or DECIMAL counter.
This is a 4 bit presettable CMOS ring counter. This counter has UP Count facility, by switch selection. DOWN Count facility by switch selection. Preset a count in the range of 0000 to 1001 in case of DECIMAL count or from 0000 to 1111 in case of BINARY count. This is achieved by setting the 4bit PRESET state switches to either at 0 or at 1 state.
Using the above counter any mode of operation can be set. A logic-1 output of this counter is used as gate trigger required for the SCR to go into active state. This in turn will act as a solid switch.
A 230V AC operated Lamp load is used to display the state of the counter. In addition 4 bit LEDs will also display the status of this counter.
In this trainer two independent solid state relay modules. Are used for connecting AC loads. This relay consists of two TRIACS. The first TRIAC gets a control signal from a digital circuit. There is an opto-isolator between the control circuit and the first TRIAC. Depending on the status of the control signal, the first TRIAC is either activated or not. When activation signal is received by the first TRIAC, it sends gate pulse to second TRIAC. Thus enabling AC load to be activated. The solid state relay used in this trainer comes in the form of a packed module consisting of opto-isolator and TRAIC devices.
This module can at best be used in conjunction with a dedicated hardware or a Microprocessor or a Microcontroller or any other data acquisition system at the time of prototype development or just for experiment. Input signal level: TTL (0 to 5v DC). Output : 230V AC @ 3A.
A switching power supply is a device transforming the voltage from one level to another. A switching-mode power supply (SMPS) is a power supply that provides the power supply function through low loss components such as capacitors, inductors, and transformers and the use of switches that are in one of two states, on or off. The advantage is that the switch dissipates very little power in either of these two states and power conversion can be accomplished with minimal power loss, which equates to high efficiency. Usually a switching-mode power supply is circuit that operates in a closed loop system to regulate the power supply output.
The switching mode power supply contains a transformer/coil and to make this as small as possible, the internal switching frequency has to be quite high, something typically in the range between 20KHz and 1MHz. This also makes the device noiseless to human ears. The oscillator noise is often conducted onto the input and output lines with a frequency that varies with the load.
This trainer consists of fundamental blocks like multivibrator, pulse width modulator, control voltage feedback, MOSFET power devices etc. This operates at 60KHZ. This trainer essentially demonstrates how SMPS works. The scope of this trainer provides necessary test points for observation of the above referred signals for study.
Specifications:
• Operates on principle of PWM• Duty cycle: 85%• Output: 5V @ 1A• Input: Unregulated at 10V• Oscillator : 60KHz• Voltage feedback circuit to determine PWM duty cycle.
Thyristors find extensive applications in power electronic circuits such as DC motor drives, large power application drive circuits etc. This trainer provides an opportunity to study, how a single phase Half / Fully controlled bridge circuit works.
This trainer has four thyristors connected in a bridge configuration. Necessary firing circuit is provided for control. It is possible to connect a resistive load to the output terminals to observe waveforms on CRO and record. A voltmeter and an Ammeter are used to measure the line and load characteristics.
Current Transformers are devices, which convert high power signals to lower, more manageable signals. This transformer encircles the wire carrying the signal and via induction transmits a proportional signal through two leads attached to the secondary side. It is also intended to perform roles for safety protection and current limiting.
They can also cause circuit events to occur when the monitored current reaches a specified level.This is done by constructing the secondary coil consisting of many turns of wire, around the primary coil, which contains only a few turns of wire. In this manner, measurements of high values of current can be obtained. A burden resistor connected across the secondary produces an output voltage proportional to the resistor value, based on the amount of current flowing through it. When choosing the burden resistor, the engineer can create any output voltage per amp, as long as it doesn't saturate the core.
This trainer is intended to study how the current transformer functions. With this it is possible to make measurements on the secondary by properly connecting the Burden resistor at the secondary. In order to accomplish this task the trainer is provided with a current transformer with maximum primary current of 1A and secondary current of 200mA for 1A input. Two independent current meters monitor both primary and secondary currents. In order to facilitate the loading of primary, a lamp load consisting of 300W is available. An external Variac ( Dimmer-stat) of at least 3A, is required to vary the input current.
At the end of the experiment, a graph depicting the primary Vs secondary current is drawn. Transformer losses are not considered at this stage.
Potential transformer (PT) is intended to measure high voltages in a circuit as a function of step-down voltage. While the PT provides a good isolation from the power circuit to measuring circuit, it is also used for safe instrumentation and control purposes. A potential transformer is an accurate transformer.
This trainer has a potential transformer with 0.003mV / V input. Using this transformation, it would be possible to measure a secondary voltage in the range of 0 to 0.69V FSD. In order to accomplish the measurements, this trainer has two suitable voltmeters one for primary and secondary voltages. The scope of experiment restricts to measurement of turns ratio and a graph between primary voltage Vs secondary voltage. Power factor measurements are not within the scope of supply.
Cycloconverters find extensive use in high power systems like locomotive drives, cement and sugar mills etc. Cycloconverters works on the principle of converting single fixed frequency AC signal to Variable frequency AC signal. This is achieved by using a center tap transformer. Four different SCRs used. Appropriate snubber circuits protect these SCRs. Volt meter and Current meters for the measurement of voltage and current within the circuit.
PHASE CONTROL CIRCUITS
Why phase control?Power systems using Thristors often exert control of load power by control of the time of firing during the AC cycle. This implies delaying conduction of the thyristor so that only a selectable portion of the AC cycle is available for the load. The non-sinusoidal voltage and current wave applied to the load has operational, measurement, analytic, and harmonic interference not encountered with straight DC or with AC sine-wave power. However, such phase-control circuits are relatively simple, efficient, and very convenient. Efficiency is high because turn on is extremely fast, and turn off is reasonably fast. Also conductive losses tend to be low because of the volt or so dropped across these devices. A good thing about using thyristor for phase controlled power is the self commutating feature, wherein turn off automatically obtains when the current wave goes through zero. The phase control can be achieved either on a full or half wave basis. A single SCR yields a half wave circuit, whereas TRIACS enable full wave operation from a single wave operation from a single device. Several relationships pertaining to phae controlled proper are often overlooked or become the sources of confusion. Best thing is to experiment and see your self what is right or for that matter why is it right.
AC regulator works on the principle of converting fixed AC voltage to a variable AC voltage operating at the same frequency. This principle is used in speed control of AC drives, pumps, illumination control, temperature control of ovens etc. The devices used for such a control are THYRISTORS. This trainer contains a THYRISTOR, necessary firing circuit, and power supply, test points for observing waveforms.
AC regulator works on the principle of converting fixed AC voltage to a variable AC voltage operating at the same frequency. This principle is used in speed control of AC drives, pumps, illumination control, temperature control of ovens etc. The devices used for such a control are TRIACS, DIACS and THYRISTORS.
This trainer is intended to provide facility to change the phase angle ? of TRIAC GATE with reference to power line frequency. As a result of this the ON / OFF state of TRIAC is varied, thereby varying RMS value is changed. In this trainer it is possible to measure the phase difference between the input and the output signal. This trainer contains a TRIAC, DIAC necessary firing circuit, and power supply. Load circuit waveforms can be observed through the test points provided. You can connect the load like fan, lamp, pumps, etc. not exceeding max 1A at the load terminal. An isolated 12 AC reference supply is available, for comparing the phase difference at various points on the circuit board, using an external dual beam oscilloscope. In order to connect external loads like fan, lamp, pumps, etc, a separate power socket is available as part of TRIAC circuit. Using this AC loads upto 1 A can be connected. It is very important to note that, HIGH VOLTAGES EXIST on the circuit board, so sufficient and enough care must be taken while measuring the circuit under study.
The entire instrument is housed in an elegant FRP cabinet.
An external dual beam oscilloscope is required for measuring and observing the waveforms.NOTE: Enough care must be taken for isolating AC signals. Qualified staff must be present while conducting this experiment.
