Electromechanical Regulators

In electromechanical regulators, voltage regulation is easily accomplished by coiling the sensing wire to make an electromagnet. The magnetic field produced by the current attracts a moving ferrous core held back under spring tension . As voltage increases, so does the current, strengthening the magnetic field produced by the solenoid and pulling the core towards the field because direction of force of core will be in the direction of maximum inductance. The magnet is physically connected to a mechanical power switch, which opens as the magnet moves into the field. As voltage decreases because discharging of capacitor is done , so does the current, releasing spring tension or the weight of the core and causing it to retract. This closes the switch and allows the power to flow once more. Electromechanical regulators have also been used to regulate the voltage on AC power distribution lines. These regulators generally operate by selecting the appropriate tap on a transformer with multiple taps with the help of moving core. If the output voltage is too low, the tap changer switches connections to produce a higher voltage. If the output voltage is too high, the tap changer switches connections to produce a lower voltage.  If the mechanical regulator design is sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector switch across a range of resistances or transformer windings to gradually step the output voltage up or down in autotransformers.

Inverters

In one simple inverter circuit, DC power is connected to a transformer through the centre tap of the primary winding. A switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.

The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer. A similar mechanism has been used in door bells.
The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply

There are many different power circuit  used in inverter designs. Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used.

The issue of waveform quality can be addressed in many ways. Capacitors and inductors can be used to filter the waveform. If the design includes a transformer, filtering can be applied to the primary or the secondary side of the transformer or to both sides. Low-pass filters are applied to allow the fundamental component of the waveform to pass to the output while limiting the passage of the harmonic components. If the inverter is designed to provide power at a fixed frequency, a resonant filter can be used. For an adjustable frequency inverter, the filter must be tuned to a frequency that is above the maximum fundamental frequency.

Many inverters are provided with a power switch, and must be turned on before they supply AC power. However some models are provided with ‘auto turn-on, so they stop working when the AC load is removed, but turn on again automatically when a load is connected. This allows the power switch of an appliance or tool to be used to control the inverter’s operation as well, conserving battery energy while still allowing the appliance to  be operated in exactly the same way as when it is  connected to the mains.

As negative sequence harmonics is most dangerous one, therefore measures should be taken to reduce them.

Actually there is a different kind of problem with many kinds of fluorescent light assembly: not so much inductive loading, but capacitive loading. Although a standard fluoro light assembly represents a very inductive load due to its ballast choke, most are designed to be operated from standard AC mains power. As a result they’are often provided with a shunt capacitor designed to correct their power factor when they are connected to the mains and driven with a 50Hz sinewave. The problem is that when these lights are connected to a DC-AC inverter with its ‘modified sinewave’ output, rich in harmonics, the shunt capacitor doesn’t just correct the power factor, but drastically reduces the stability, because its impedance is much lower at the harmonic frequencies , since frequency increases when harmonics are present and thus capacitance decreases which further decreases impedence. As a result, the fluoro assembly draws a heavily capacitive load current, and can easily overload the inverter.

The most common type of pure sinewave inverter operates by first converting the low voltage DC into high voltage DC, using a high frequency DC-DC converter. It then uses a high frequency PWM system to convert the high voltage DC into chopped’ AC, which is passed through an L-C lowpass filter to produce the final clean 50Hz sinewave output. 

Smart Sensors

An intelligent temperature transducer (smart sensor) has a built-in transducer electronic data sheet (TEDS) to make the measurement conversion and provide the data in units of temperature to the network controller which may contains processors. To do this, the smart sensor module also contains the digital interface to provide a communication channel between the network control and the smart sensor.

There are two main components of a functional smart sensor:

1) a transducer interface module (TIM) and 

2) a network capable application processor (NCAP)

TIM

A TIM  contains the interface, signal conditioning, Analog-to-Digital and/or Digital-to-Analog conversion and in many cases, it also contains the transducer. A TIM can range in complexity from a single sensor or actuator to many transducers including both sensors and actuators.

NCAP

An NCAP is the hardware and software that provides the gateway function between the TIMs and the user network or host processor (the transducer channel).

A transducer channel is considered 'smart' because of three features:

•  It is described by a machine-readable, Transducer Electronic Data Sheet (TEDS).
•  The control and data associated with the transducer channel are digital.
• Triggering, status, and control are provided to support the proper functioning of the transducer channel.

An NCAP or a host processor, controls a TIM by means of a dedicated digital interface medium. The NCAP mediates between the TIM and a user defined digital network. The NCAP may also provide local intelligence.

In brief, the smart sensors can perform there tasks in following sequence.

Self calibration:

Self-calibration means  to adjust the deviation of the output of sensor from the desired value when  the input is at minimum or it can be an initial adjustment of gain. Calibration is needed because their adjustments usually change with time that needs the device to be removed and recalibrated. If it is difficult to recalibrate the units once they are in service, the manufacturer over-designs, which ensure that device, will operate within specification during its service life. These problems are solved by smart sensor as it has built in microprocessor that has the correction functions in its memory.

Computation:

Computation also allows one to obtain the average, variance and standard deviation for the set of measurements. This can easily be done using smart sensor. Computational ability allows to compensate for the environmental changes such as temperature and also to correct for changes in offset and gain

Communication:

Communication is the means of exchanging or conveying information, which can be easily accomplished by smart sensor. This is very helpful as sensor can broadcast information about its own status and measurement uncertainty.

Multisensing:

Some smart sensor also has ability to measure more than one physical or chemical variable simultaneously.  A single smart sensor can measure pressure, temperature, humidity gas flow etc.

 From the definition of smart sensor it seems that it is similar to a data acquisition system, the only difference being the  presence of complete system on a single silicon chip.