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Audio Frequency Range and Electronic Components

A vast majority of people like to listen to some form of audio. Be it in cars, homes, or theaters, audio is prevalent, and its applications are growing with the increasing use of portable devices. In all audio systems, important factors for a portable audio device are its design, size, cost, and quality. But listeners judge the performance of an audio device primarily on the basis of its capability to recreate the necessary audio frequencies.

The audio industry commonly refers to the frequency range that humans can hear and perceive as 20 Hz to 20,000 Hz. Although the average human can distinguish far less than this range, the ability depends on the age and health of the individual. For instance, with age, this range inevitably shrinks, with the loss being more pronounced at the higher frequencies.

Experts divide the perceptible audio spectrum into seven subsets. Starting with the sub-bass subset whose frequency ranges from 16 to 6 Hz, is the primary low range of musical instruments. Then comes the bass frequencies ranging from 60 to 250 Hz, and this is the normal speaking vocal range. Next is the lower mid-range of brass and wood instruments covering the range of 250 to 500 Hz. Mid-range frequencies follow next, covering 500 Hz to 2 kHz, where the higher end of fundamental frequencies of most musical instruments lies. The next range is the higher mid-range, covering 2 to 4 kHz, where the harmonics of most instruments are present. The next range is the presence ranging from 4 to 6 kHz, and this is where the harmonics of string instruments are. The last subset is the brilliance, ranging from 6 to 20 kHz, where the most whiles and whistles are present, and where the harmonics of most percussion instruments lie.

For visualizing and quantifying audio frequencies generate by most audio devices and electronic components, experts rely on frequency response graphs. These graphs are a plot of the sound pressure level at a specified distance plotted against frequency. For instance, a buzzer puts out an audible tone, which features a narrow frequency range on the response graph. On the other hand, audio speakers feature a wide frequency range coverage, as they must recreate sound and voice more faithfully.

A typical frequency response graph for electronic components generating sound depicts the sound pressure level or loudness on its Y-axis on a logarithmic scale, while the X-axis represents frequencies on a logarithmic scale. For electronic devices that sense audio input, such as microphones, the frequency response graph shows sensitivity as sound pressure level on the Y-axis on a logarithmic scale. Most of the frequency response graphs represent a constant power input to the device under measurement.

The frequency response graph is an important document for selecting electronic components for a specific application. For instance, it can differentiate whether a particular speaker will be a good performer for the entire audio frequency range, or it will be suitable for bass frequencies alone. Similarly, the frequency response graph for a microphone will characterize it as suitable for a concert or for instrumentation.

Hybrid Plug-in Connectors for Motor Control Systems

Motor control systems are increasingly becoming more compact while their use is growing with applications in Industry 4.0 and Industrial Internet of Things (IIoT). In fact, motor control systems are prevalent in varied industries like food and beverages, material handling, and robotics. However, as the size of the controller shrinks, designers are facing a new challenge—routing power and signal easily and cost-effectively—while ensuring operator safety and electromagnetic compatibility.

One can use advanced open source interfaces to connect both power and data signals with a single compact connector. Although this does simplify connectivity, the quality, design, and performance of the connector become critical to ensure signal integrity, EMC, and compliance with IP20 requirements.

Designers have moved to Hiperface DSL and SCS open Link, open-source interfaces, to allow the same connector to carry both power and data. This not only saves space but also lowers the cost and simplifies the design of high-performance motor controllers.

The communicating cable has two shielded wires for bi-directional communication based on RS-485, and other wires for encoder power, motor power, and motor brake controls. There are three elements—a three-phase power supply cable, a shielded motor brake cable, a shielded data pair for digital data transfer—enclosed within a shielded cable.

The Hiperface DSL offers a data transmission rate of 9.375 MBaud, over a cable distance of up to 100 meters between the motor controller and the motor. It is possible to transmit data on the cable in two ways—cyclically, given signal and noise conditions, or synchronously with the controller clock.

The motor feedback interface design of the SCS open Link system can supply bidirectional data between the motor and controller. This includes encoder data at rates up to 10 MBaud. It is possible to use two or four-wire implementation. This link is optimized for Industry 4.0, and especially for emerging IIoT solutions, including motor condition monitoring and predictive maintenance.

For SCS open Link and Hiperface DSL to operate reliably, the connection needs optimum shielding between the motor/encoder and its drive. The number of interfaces reduces with the use of plug-in connectors and connection terminals. It is also important to have unbroken shielded cables between the motor/encoder and the drive. However, as the drive connector is non-standard, designers must be careful when designing their own connectors for meeting performance requirements.

OMNIMATE Power Hybrid connectors are an alternative to the SCS open Link and Hiperface DSL. These are a three-in-one solution providing signal, power, and EMC features that implement the SCS open Link and Hiperface DSL protocols. Moreover, the hybrid connectors save space on the motor drive printed circuit board and in the controller cabinet.

The hybrid connectors are available in several configurations. These include six-, seven-, eight-, and nine-position connections. They include power and signal contacts with push-in wire connections. The pitch is 7.62 mm, conforming to the IEC 61800-5-1 and UL 1059 Class C 600 V standards. Several practical design features in the connectors provide high reliability. For instance, the adequate separation between encoder and power connections ensures minimum EMC.

Connectivity Opportunities with 5G

Various parts of the world use different connectivity standards. While some are still struggling with 2, 3, and 4G connectivity, more progressive countries are trying out 5G and 6G. However, since 2019, when the markets introduced 5G, there has been considerable interest in its features. Smartphone manufacturers are now launching new handsets that offer the promise of substantially faster internet access along with the most advanced functionality.

So far, several mobile networks have adopted 5G, the latest and fastest protocol in the market. The recent pandemic forced millions to work from home remotely, and the high-speed wireless communication that 5G offers, came at the most opportune moment.

While manufacturers are busy offering the latest generation of mobile phones to access the 5G wireless telecommunications, many are still not aware of the true impact that the 5G technology has brought us overall. While 5G is a powerful tool for consumers, they are not the sole beneficiaries. 5G is slated to impart a far greater impact to the industrial world as compared to what any other network has so far. In fact, the data speeds offered by 5G are even challenging those from the more traditional wired technologies. This is the first time the world can unshackle itself from a physically wired net.

The introduction of the Internet of Things (IoT) has started the Fourth Industrial Revolution rolling. The IoT brings with it machine-to-machine communications, which, in its basic form, allows electronic devices to share data and communicate without requiring any human intervention. The introduction of 5G began at home, where machines are dominating several tasks in everyday life like grocery shopping to energy metering.

Nevertheless, IoT in future homes is only the tip of the iceberg. The functionality that IoT offers to designers is mind-boggling. The manufacturing world is now reveling in the creation of the smart factory, a byproduct of the Industrial Internet of Things (IIoT).

A traditional factory has several machines, each performing their own tasks, totally isolated from their neighbors. IIoT connects all machines into a network that allows the entire shop floor to act as a single entity. Sharing information among themselves, machines manage not just the production schedules, but also take care of the supply chain, logistics aspects of the operation, and their own maintenance.

With the introduction of 5G communication, the industrial environment will begin to integrate more devices into the smart factory network. A private 5G cell can handle the entire facility while allowing high-speed data flow from all parts of the factory operation, beginning from sensors to the operation of the largest machines. The introduction of a wireless network in the factory brings substantial benefits like unparalleled flexibility. Manufacturers can easily reconfigure production lines to respond to newer demands from the market.

5G communications are not limited to inside the factory premises alone. One of the major users of 5G technology is the automobile industry. While the demand for electric vehicles is growing at a tremendous pace, vehicles are fast becoming autonomous or self-driven. This requires vehicles to communicate with their neighbors on the road. 5G ensures fast communication to promote safety.

Solderless CoB LED Holders

CoB or Chip-on-board LEDs are very popular for producing high-power lights. Many connector manufacturers provide easier and faster methods for setting and mounting the CoB LEDs in lighting fixtures. One of them is the solderless LED holders, focusing on easy and fast assembly, secure attachments, and lower costs. Numerous companies are now offering solderless CoB LED holders.

An LED holder typically holds the CoB LED before mounting on the heat sink. As the operator screws the holder on to the heat sink, the holder pushes the LED on the heat sink to allow good heat transfer. The holder also allows making electrical connection to the LED. In addition, the holder provides isolated landing zones for secondary optics such as lenses and reflectors.

TE Connectivity is one of the major producers of solderless holders for CoB LEDs. Their Z50 connector from the LUMAWISE family, conforming to the Zhaga consortium specifications, is the latest. The specifications stress on the interchangeability of light-sources and simplify general LED lighting arrangements.

Assembling the Z50 takes only five easy steps:

Snap the CoB into the base
Apply thermal grease to the LED
Fit cables into the Z50 base
Screw the assembly on to the heat sink
Attach secondary optics

The Z50 is available in various designs compatible with LEDs from different manufacturers. These include the SOLARIQ array, Nichicon CoB, OSRAM Opto, Philips LUMEDS, and the CXA series from Cree. One can use the holder in different ways such as for stage lights, wall washers, downlights, architectural lighting, and spotlights.

Molex offers PSI or plastic-substrate interconnect suitable for LED CoB arrays. Molex has designed these holders such that users can achieve a secure connection very fast. The interconnects are customizable as they address space constraints. Lighting designs often demand low-profile harness interfaces that the PSI addresses very well. A simple connection to the holder delivers power to the array.

Ideal for area lighting and down-lighting, the PSI system from Molex is available in custom shapes including the more common rectangular and circular as well. Other low-profile receptacles and headers are also available from Molex.

Solderless LED connectors are also available from VCC, such as their CNX 460 and CNX 440 series. The receptacles are unique as they require no tools for assembly, offering an easy and quick threaded connection. It is possible to configure the CNX 440 series to make it support up to 6 leaded IR, UC, or RGB LEDs at a time. On the other hand, it is possible to use the CNX 460 for standard 10 mm LED packages or high-flux LEDs. Both series can work with LED brands from all major manufacturers. For increased brightness, VCC offers HMC 461 and CMC 441, with Fresnel ring lens style. NEMA 4 applications can use HMC 4661 and CMS 442, also from VCC.

Providing extra stability to the leads of the LED, the CNX 460 and CNX 440 series of LED connectors have unique interconnectors. VCC has designed the connectors to easily integrate them within standalone assemblies or custom cable assemblies providing wire ends stripped for PCB connection. No crimping or soldering is necessary, as the modular panel mount from VCC offers easy and superior connection and stability.

What is Industrial Connectivity?

Engineers include any component involved in the path of delivering control signals or power for doing useful work as part of industrial connectivity. Typically, components such as terminal blocks, connectors, motor starters, and relays are part of industrial connectivity.

Engineers divide industrial connectors into four categories depending on the environments in which they operate—commercial, industrial, military, and hermetic. Commercial applications do not consider temperature and atmosphere as critical operating factors affecting performance. Industrial applications require connectors capable of handling more rugged environments involving hazards such as sand, dust, physical jarring, vibration, corrosion, and thermal shock.

Most general connectors use low-cost materials to merely maintain electrical continuity. However, designers have a large variety of materials from which to choose for making connectors. These include brass, beryllium copper, nickel-silver alloys, gold, gold-over-silver, gold-over-nickel, silver, nickel, rhodium, rhodium-over-nickel, and tin.

No wire preparation is necessary for use in terminal blocks. The user only needs to strip the insulation and install the wire using a screwdriver. One can use a wide range of wire sizes with terminals that provide an easy way to hookup wires from different components, ensuring fast connection/disconnection during troubleshooting and maintenance.

Manufacturers make terminal bodies from a copper alloy with the same expansion coefficient as the wire it connects. This prevents uneven expansion from causing loosening between the connector screws and the wire, avoiding an increase in contact resistance. Using similar metals also avoids corrosion, usually with two different metals in contact, as a result of electrolytic action between them.

SSRs or Solid-State Relays control load currents passing through them. For this, they use power transistors, SCRs, or silicon-controlled rectifiers, or TRIACs as switching devices. Engineers use isolation mechanisms such as optoisolators, reed-relays, and transformers for coupling input signals to the switching devices to control them.

To reduce the voltage transients and spikes that load-current interruptions typically generate, engineers use zero-crossing detectors and snubber circuits, incorporating them within solid-state relays.

Semiconductor switches generate significant amounts of waste power, and engineers must minimize their operating temperature using heat sinks attached to solid-state relays. SSRs can operate in rapid on/off cycles that would wear out conventional electromechanical relays quickly.

Electromechanical relays physically open and close electrical contacts for operating other devices. In general, they cost much less than equivalent electronic switches. They also have some inherent advantages over solid-state devices. For instance, the input circuit in electromechanical relays is electrically isolated from the output circuits, and one relay can have more than one output circuit, each electrically isolated from the others.

Furthermore, the contact resistance offered by electromechanical relays is substantially lower than that offered by a solid-state relay of a similar rating. The contact capacitance is lower as well, benefitting high-frequency circuits. Compared to solid-state relays, electromechanical relays are far less sensitive to transients and spikes, not turning on as frequently as SSRs do. Brief shorts and overloads also damage electromechanical relays to a far less extent than the damage they cause to SSRs.

Improved manufacturing technology is now making available electromechanical relays in small packages suitable automated soldering for PCB mounting and surface mounting.

IoT and DIP Switches

Pre-configuring equipment helps in many ways. In the field, the ability to pre-configure functionality eases installation procedures, helps in diagnostics, and reduces downtime. DIP switches are very popular for pre-configuring devices and an increase in their demand is accelerating the flexibility in their design.

Although designers nowadays prefer to use re-programmable memories and software menus in equipment, DIP switches customizing the behavior of electronic devices was have always been present. DIP switches present an easy-to-use method for changing the functionality that anyone even without software knowledge can use. An added advantage of DIP switches over software menus is the former allows change even when the equipment has no power.

Engineers developed the DIP switch in the 1970s, and their usefulness remains relevant even after five decades, for instance, for changing the modality of a video game or for fine-tuning the operation of a machine on the shop floor. Now, engineers are finding new uses for this proven technology in innovative applications such as the IoT or Internet of Things.

Depending on present requirements, manufacturers now present a large variety of DIP switches for modern applications. It is now easy to find surface mount versions of DIP switches, with SPST or single pole single throw, SPDT or single pole double throw configurations, or multi-pole single and double throw options. Piano type side actuated DIP switches, side DIP switches, and DIP switches in sealed and unsealed versions are also available readily off the shelf.

Originally, DIP switches were a stack of manually operated electric switches available in a compact DIP or dual-in-line package with pins. The configuration of the pins of a DIP switch was the same as that of an IC with leads, which made it easy for a designer to incorporate in the printed circuit board. It was usual for each switch to have two rows of pins, one on each side. The distance between the rows was 0.3”, while the pitch or gap between adjacent pins was 0.1”. By taking advantage of the same mounting technique as that of an IC, the DIP switch provided a compact switching mechanism that designers could place directly on the PCB.

By stacking DIP switches side by side, the designer could add as many switches to the circuit as necessary. The versatility of the DIP switch lay in the numerous configurations achievable. For instance, it is possible to generate an incredible 256 combinations from an eight-position DIP switch. Each switch can assume one of two ways, and an eight switches combination can assume one of 256 ways (2 to the eight power).

Earlier, digital electronics mostly used eight bits to a byte, which made the eight-position DIP switch more of a standard at the time. With advancements, digital electronics now encompasses 8, 16, 32, 64, 128, and even 256 bits, generating a great demand for DIP switches with new designs.

DIP switches are easier for the user as they offer a visual indication of the present setup. For manufacturers, DIP switches make it easier to customize their production, at the same time, allowing the user to make changes as necessary.

Sensor Technologies for Air Quality Monitoring

Although air is all around us, we breathe it in every minute, and our lives depend on it, yet we pay very little attention to the quality of air, unless when facing a problem. Whether it is indoors or outdoors, poor air quality can affect our health and well-being significantly. Two levels of air pollution measurement are significant here.

One is the presence of small PM2.5 or Particulate Matters measuring less than 2.5 microns in size—one micron being one-micrometer equal to one-millionth of a meter or one-thousandth of a millimeter. The other is the presence of VOCs or Volatile Organic Compounds.

Combustion processes emit PM2.5 type of pollutants, for instance, by fires burning in fireplaces and lit candles within the house. Cleaning textiles, furniture, and supplies can emit VOCs. Engineers and scientists are working on improving sensing technologies to enable monitoring PM2.5 and sensing VOC by personal air quality monitoring systems for improving the health and well-being of the people.

According to the WHO, PM2.5 enters our lungs easily causing serious health problems such as chronic and acute respiratory diseases, asthma, lung cancer, heart diseases, and stroke. A recent study by Harvard University links PM2.5 exposure to sensitivity to viral diseases such as SARS-CoV-2.

While one does receive averaged or consolidated data from official air quality monitoring stations, that data is for the outdoor environment only. For indoor air pollution monitoring, a portable air quality measuring device, also known as a dosimeter, is more appropriate—especially when incorporated within a wearable or a smartphone. So far, PM2.5 sensors were too large for mobile devices. Bosch Sensortec now has sensors that make it possible to incorporate them into personal devices.

The Bosch PM2.5 technology offers sensors small enough to incorporate within wearables and smartphones for measuring the daily exposure of a person to PM. The person can see data and trends of local pollution levels to which they are exposing themselves, and take appropriate actions to minimize their exposure for improving their health and well-being.

BreezoMeter uses PM2.5 sensor technology from Bosch Sensortec to make PM2.5 Dosimeters. They also offer an app for the Dosimeter that collates local data measured by the Bosch PM2.5 sensor and the air pollution data from the BreezoMeter to calculate and display the personal daily PM exposure.

Conventionally, PM sensors rely on a fan to draw air through a cell, where optical arrangements count the particulate matter and calculate the concentration per unit of volume. This arrangement requires the sensor to be the size of a matchbox, incapable of incorporating within a smartphone.

PM2.5 sensor technology that Bosch Sensortec has developed functions on natural ambient airflow. The principle is rather like a camera, with three lasers integrated behind a glass cover. To prevent damage to the user, Bosch uses Class 1 lasers that are eye-safe. The entire arrangement is flat enough like a smartphone camera is, making it easier to incorporate within one, and using only 0.2% of the volume of air that other solutions on the market typically use.

Wireless Charging for Drones

Drones face a significant operating challenge—their limited battery capacity places a constraint on their flight time. More flexible and efficient recharging solutions can address this issue. A 4-year old startup, WiBotic, now has funding to explore this avenue. WiBotic designs and manufactures solutions to charge robot and drone batteries.

WiBotic offers power optimization and wireless charging solutions for mobile, aerial, marine, and industrial robots. Their Adaptive Matching technology is a new method for inductive power transfer. The company is providing power levels necessary for charging flying devices such as drones.

Software libraries monitor battery charge parameters in detail for providing optimization solutions. Combined with wireless charging hardware, the strategic deployment of these software features helps with the optimization of drone uptime. Wireless charging solutions from WiBotic also schedule the recharge, allowing multiple drones to charge from the same transmitter at various times.

Nikola Tesla was the first to demonstrate, in the late nineteenth century, the use of electromagnetic fields as a source of electricity transfer without wires. Although engineers are aware of the wireless methodology, the design of an entire system consisting of transmitters and receivers, their locations, and maximizing their efficiency is a complex challenge requiring specific skills. Most wireless power transfer systems use inductive coupling or magnetic resonance with their individual strengths and weaknesses.

Inductive coupling is the most common method, usually found on consumer devices. However, they are efficient only when the transmitter and the receiver antennas are close together. Therefore, this method is not suitable for drones and robots as they cannot position themselves so that their inductive systems are close enough to provide a reliable power transfer.

The technology of magnetic resonance is one of the latest providing more flexibility in positioning. Most magnetic resonance systems have a special area for delivering power with maximum efficiency. If the robot or the drone stops in this area only briefly or remains off-center, the charging efficiency reduces, and the charging time increases.

WiBotic technology incorporates the best of both systems and operates on the strengths of both resonant and inductive systems. They have a patented Adaptive Matching system to constantly monitor relative antenna positions, while dynamically adjusting both hardware and firmware parameters for maintaining maximum efficiency. This ensures delivery of high-power levels and reliable charging, even when several centimeters of angular, horizontal, or vertical offsets separate the transmitter and the receiver.

For drones, the WiBotic wireless charging station is a square platform of about 3 ft x 3 ft. It has an intelligent induction plate that determines the type of battery the drone has and establishes the proper charging parameters for it.

WiBotic wireless charging systems all have four primary hardware components—the transmitter antenna coil, the receiver antenna coil, the on-board charging unit, and the transmitter unit.

Using an AC source, the transmitting unit produces a high-frequency wireless signal, that travels to the transmitting antenna coil and generates electric and magnetic fields.

The transmitter unit has the capability to recognize an incoming drone equipped with a receiver antenna coil, which automatically activates itself to receive the right amount of energy.

Protecting Against Ground Faults

Faults are instances of something happening when it should not. Electrical faults are when electric current flows where it should not be flowing. Electric current flowing from the live wire to the ground in place of the customary neutral wire constitutes a ground fault.

There are two major problems that a ground fault may cause. One is excessive current may cause overheating and fire may break out. The other is a ground fault could be fatal for any person being a part of the ground circuit. That is why it is important to protect against ground faults occurring.

Earlier to the 1970s, people did not realize the necessity of grounding electrical systems. As a result, most industrial and commercial systems remained ungrounded. Although ungrounded systems do not result in significant damage, the numerous disadvantages that they present led to a change to grounded systems. Grounded systems also help in protection against lightning, and reduction of shock hazards.

In electrical supply and distribution systems, faults are mainly of two types—phase-to-phase faults, and ground faults—with ground faults being 98% of them. While fuses form the main methods of protection in case of phase-to-phase faults, protecting against ground faults requires the additional use of protective relays.

For instance, a toaster may have the hot wire shorted to its metal casing. Turning on the toaster causes all or a part of the current to pass through the toaster frame and then on through the green ground wire. If the current is high enough, the circuit breaker will trip. Adding a ground protection relay would have detected the current flow at a significantly lower level and opened the circuit much quicker than the circuit breaker.

Ground faults occur for different reasons. These could be due to inclement weather, causing a tree to fall over and rest on power lines during a storm. Insulation degraded by age can also cause ground faults—heat from a current flow can break down old insulation. Moisture from high humidity can break down insulation. Excessive overvoltage and puncture the insulation and cause ground faults.

Protecting against ground faults means isolating the circuit with the fault so that there is no power to that part of the circuit. However, to clear the fault, it is necessary to first establish the presence of a fault, and then determine the source of the fault. System designers use a ground fault protection relay for this purpose.

In normal operation, electric current flows from the phase or hot wire into the appliance and returns via the neutral or the cold wire. As the two currents are equal, their resultant electromagnetic fields cancel out. A current transformer placed across the phase and neutral wires will yield zero output while the two wires carry equal currents.

In case of a ground fault, part or all the current from the phase wire bypasses the neutral wire, since it now flows through the ground wire. As the two currents through the CT are now unequal, there is a resultant output from the CT, tripping the associated circuit breaker.

What are Motor Starters?

Starting up small motors is usually through a manual starter that can make or break the power supply line to the motor. The method is also known as DOL or direct online start. If the motor gets too hot due to an overload, a thermal protection circuit in the starter opens and disconnects the motor. DOL starters are the most common method of starting and stopping single-phase motors up to 5 HP, 230 VAC, and three-phase motors up to 15 HP, 600 VAC.

Magnetic starters can have controls such as float switches, pressure switches, timers, relays, limit switches, and push buttons, as they have a separate mechanism for closing and opening a set of contacts for the motor circuit. They also include a thermal overload protection device. The mechanism consists of a coil, which, when energized, closes contacts to complete the electrical circuit of the motor. Likewise, de-energizing the coil opens the contacts, switching off the motor.

However, one of the problems with DOL or magnetic starters is both allow the motor to start with a high current. Under normal conditions, motors must start with a current that is nearly 6 to 7 times the rated running current of the motor. This is necessary for the motor to overcome the initial torque due to friction. However, for some motors, the starting current can go up to 9-10 times the rated current.

Reversing any two phases of a three-phase induction motor results in the motor reversing its direction of rotation. Adding an extra set of contacts to a basic starter can turn it into a reversing starter. Appropriate electrical and mechanical interlocking mechanisms must also be present for safeguarding the motor operations.

A soft starter applies a low voltage to the motor, ensuring a low starting current and torque. The torque gradually increases as the soft starter begins to apply higher voltage. Semiconductor switches such as thyristors, inside the starter, accomplish the gradual increase in the voltage that the starter applies to the motor.

A slow start is essential to prevent stress on the internal components of the motor, and to the machinery, the motor is driving, especially belts and gear drives. The soft starter also features soft stopping. This is essentially helpful for stopping conveyor belts and pumps, where a sudden stop may cause water hammering in the pipe system.

Multispeed induction motors have multiple windings that require special starters. For instance, two-speed motors with separate windings need starters with two built-in standard starters within a single enclosure with mechanical and electrical interlocks.

Consequent-pole two-speed motors need a three-pole starter unit or a five-pole starter unit. The design of the motor winding determines whether the three- or five-pole unit makes a slow-speed or fast connection.

Delta-type multi-speed motors require different power circuits for the currents circulating within the unconnected and inactive windings. Two-speed motors with separate open-delta windings require a pair of four-pole starter. For each speed, a different four-pole starter is necessary. Therefore, very complex starters are necessary for motors with open-delta windings capable of running at three or four speeds.