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Low-Side & Hi-Side Current Sensing

Electronic systems tend to manage their power consumption to reduce the production of heat as waste. This calls for optimizing the system efficiency by effectively distributing power. As the voltage applied to the circuit is usually a constant, engineers monitor power consumption by keeping track of the current drawn by the circuit—power being the mathematical product of the current and voltage fed to the circuit. Current sensing has additional advantages, mainly that of maintaining the health of the system, preventing circuit faults from turning disastrous, and preventing batteries from over-discharging.

Engineers use two basic methods to monitor electric current. The first method follows Ampere’s law, and engineers measure the magnetic field surrounding a current-carrying conductor. The second method follows Ohm’s law, and engineers measure the voltage drop across a small resistor inserted in series with the circuit. The first is a non-intrusive method, but useful only for regularly changing currents, such as alternating current. It is also an expensive method, rather prone to temperature coefficient errors and effects of non-linearity. The second method is simpler, but introduces an element of insertion loss.

The semiconductor industry offers resistive-sensing techniques that are cost-effective and accurate, while making measurements suitable for various applications running on direct current. The resistive-sensing technique relies on sensing the current on the low-side or on the high-side of the circuit, the optimal approach depending on the application.

In resistive sensing, engineers insert a low-value resistor in series with the current path. This produces a small voltage drop in proportion to the current the circuit is consuming and which passes through the resistor. An electronic sense amplifies this tiny voltage to make it easier to process further. However, the sense resistor’s placement depends on the environment of the application and this can present some serious challenges for the sense amplifier.

If the position of the sense resistor is between the load and the circuit ground, a single operational amplifier, acting as a sense amplifier, is adequate to amplify the resulting voltage drop. Engineers call this low-side sensing, and is different from high-side sensing, where they place the resistor between the positive lead of the supply and the load.

In both cases, the sense resistor must be of adequately low value to prevent it from dissipating high power, but its value must be high enough for it to generate a detectable voltage for the sense amplifier to multiply it accurately. The sense amplifier multiplies the difference of voltage across the sense resistor, but uses a common-mode voltage for the purpose.

For low-side sensing, the common-mode voltage is close to the ground, and the rest of the circuitry following the sense amplifier may run on low voltage. However, high-side sensing requires the common voltage to be close to the supply voltage, and sometimes this may be high enough to present supply voltage problems for the circuit following the sense amplifier.

Some applications are unable to tolerate the tiny voltage drop introduced by the sense resistor on the low-side. The situation aggravates as the load current increases. For them, engineers have to follow high-side sensing inevitably.

What are Ball Grid Arrays?

Initially, surface mount devices, especially ICs, came as perimeter-only packages, with pins for soldering placed along the edge of the device. As ICs became more complex, they needed more pins for external interfacing, which made the packages larger. Manufacturers soon realized there was a large unused real estate that lay just under the package. Therefore, they made the ball grid array (BGA) packaging, which, in place of pins, had solder balls aligned in a grid under the device. Soldering BGAs involves melting these solder balls onto pads on the PCB.

Using BGAs leaves a considerably larger area free on the PCB. Compared to mounting a package with pins on its perimeter, BGAs offer better thermal and electrical properties, and this has made the format popular, following the continued miniaturization of electronics.

Since their introduction, although their basic concept has remained the same, BGAs have changed in dimension and now come with far smaller pitches and smaller outlines. There are varieties as well, with some packages having connections only on the periphery and none at the center, while others have the connections distributed evenly across the bottom of the package.

For simpler BGAs, routing traces on the PCB is simple as the balls are placed well apart or there is space in the middle of the device. However, with increasing pin counts and decreasing pitches, routing between the pins becomes more difficult, resulting in increasing the layers of the board, thereby increasing the cost and reliability concerns.

As BGAs become increasingly more complex, designers have to depend on vias to connect the BGA with the rest of the circuitry on the PCB. Vias are small holes drilled through the multilayer PCB and plated with copper to provide connection between pads and traces on different layers. Some vias are through-hole types, meaning they start and end on the two extreme layers of the PCB, and may connect to other layers in between. Other vias can be blind types, starting from one of the outermost layers and ending on an internal layer, possibly connecting other layers in between. Blind vias are not visible on the PCB surface as they start and end at different internal layers, and may connect other internal layers as well. However, all the above require great precision while manufacturing, and are expensive processes.

Ordinarily, PCB designers prefer not to use vias on a pad, as during soldering, vias can wick solder from the pads leaving the joint in a dry and unsoldered state. However, with BGA pitches getting increasingly smaller, designers do not have much choice, but tenting is offering a way out. Tenting allows filling the via hole with an insulating material and covering the top with a layer of copper, thereby preventing wicking.

As the BGA pins lie in between the device body and the PCB, traditional soldering methods such as hand soldering and wave soldering are no longer useful, and assemblers rely on infrared heating or reflow ovens to solder BGAs to a PCB. This requires a pick-and-place machine placing the BGA package precisely on the pads and uniformly heating the area to form the actual connections.

How Do Power Supplies Share Current?

Those who use power supplies to run different devices often face a peculiar problem. The load may demand more power from a single power supply that it can safely provide continuously. Since the voltage to the load has to remain constant, the situation calls for using additional power supplies to supply the excess current, and inevitably, users must connect them in parallel. However, simply connecting power supplies in parallel does not guarantee they will share the load current between them in an acceptable manner to operate normally.

Although designers do design some power supplies with dedicated circuits within them to ensure proper sharing of load current when connected in parallel, this is not a generalized practice. Moreover, even if power supplies of one manufacturer can optimally share current when connected in parallel, they may not do so when operating in parallel with power supplies from another manufacturer. In fact, power supplies from the same manufacturer but different models may also not work satisfactorily in parallel.

Theoretically, an ideal voltage source will supply unlimited amounts of power all the while maintaining a constant voltage level. Real power supplies have a limit to the amount of current they can supply to the load. If a load wants to draw power beyond the capacity of the supply, it will reduce its output voltage such that the power delivered remains within its capacity. Should the demand for current increase further, the output voltage reduces further until it reaches zero, and the power supply shuts down. Recovering automatically or through an external reset from an over-current situation is a design feature.

In reality, all voltage sources come with a positive and non-zero internal impedance. This drops the output voltage at the terminals as the load current increases. Power supply specifications call this change in output voltage with load current as the load regulation, and this is specific to each power supply. As the requirement is to have the output voltage change as little as possible with increasing current, some power supply designers prefer to design for low output impedances. Some power supplies have remote voltage sensing to boost the output voltage by the amount it has drooped. However, this is not desirable when sharing current.

One of the problems in connecting power supplies in parallel to supply higher current than either can supply is the current balance characteristics of the units may not match. In case the error in the initial voltage settings between the units is bigger than the depression in the output voltage at maximum load, the first unit may supply its entire share before shutting down. This leads to the second unit attempting to deliver the load current, and since it cannot do so, it shuts down as well.

One of the methods to enable proper current sharing is to enhance the output impedance of each unit so that their individual output voltage droops at full load is far more than the no-load voltage difference between the units. Although the voltage regulation of the system degrades significantly due to the intentional voltage droop, the current sharing between the power supplies is more successful.

What is 3D MLC NAND Flash Memory?

To unleash performance fit for the next generation of computers, Transcend has released its MTE850 M.2 Solid State Device (SSD), based on 3D MLC NAND flash memory. The device utilizes the PCI Express Gen3 x4 interface and supports the latest NVMe standard. According to Transcend, this SSD targets high-end applications such as gaming, digital audio and video production, and multiple uses in the enterprise. Typically, such applications demand constant processing of heavy workloads, while not willing to stand any system slowdowns or lags of any kind. Transcend claims the MTE850 M.2 SSD will offer users high-speed transfers and unmatched reliability.

High Speeds for High-End Applications

As the above SSD uses the PCIe Gen3 x4 interface and follows NVMe 1.2 standard, it transmits and receives data on four lanes simultaneously. This results in the SSD working at the blazing speeds of up to 1100 MBps while writing, and up to 2500 MBps while reading.

Why the PCIe Interface

Presently, the most popular method of connecting a host computer to an SSD is through SATA or Serial ATA interface. However, PCIe uses one transmit and one receive serial interfaces in each of the four lanes, the PCIe interface is much faster than SATA is, and it is able to fulfill new performance requirements in better ways.

Why the NVMe Standard

The growing needs of enterprise and client applications demands better performance vectors than the Advanced Host Controller Interface (AHCI) can provide. The NVM Express (NVMe) fulfills this enhanced host controller interface standard, which also calls for low latency, increased IOPS, and scalable bandwidth.

What is 3-D Expansion?

Existing planar NAND memory chips are arranged in the form of flat two-dimensional arrays. In contrast, 3-D NAND flash has memory cells stacked in the vertical direction as well as in multiple layers. This breaks through the density limitations of the existing 2-D planar NAND, with the 3-D NAND offering a far greater level of performance and endurance.

With Better Endurance Comes Higher Reliability

To help keep data secure, Transcend has engineered their MTE850 M.2 SSD with a RAID engine (a type of data storage virtualization technology) and Low-Density Parity Check (LDPC) coding, along with an Elliptical Curve Cryptography (ECC) algorithm. Additionally, Transcend manufactures their SSDs with top-tier MLC NAND flash chips and provides them with engineered dynamic thermal throttling mechanism. This way, Transcend ensures the MTE850 delivers superior stability and endurance befitting for high-end applications.

SSD Scope Software

Users can download the SSD Scope software application free of charge from the Transcend site. The application helps to monitor the health of the running SSD using SMART technology and allows the user to enable the TRIM command to obtain optimum write speeds. Using the application also keeps the firmware of the SSD up-to-date, and helps in migrating data from the original drive to the new SSD with only a few clicks.

With certificates from CE, FCC, and BSMI the #-D MLC NAND flash memory based  MTE850 M.2 SSD from Transcend works on 3.3 VDC ±5%, operating within 0 and 70°C. With mechanical dimensions of 80x22x3.58 mm, the SSD weighs only 8 grams.

What are Synchronous Condensers?

All manufacturing and industrial plants around the world face the unique problem of lagging power factor. Ideally, the voltage and current vectors should align perfectly for any AC power system feeding a load. In actual practice, however, the current either leads or lags the voltage by a few degrees, depending on whether the load is capacitive or inductive. Power factor is the cosine of the angle the current vector makes with the voltage vector as the reference. A positive power factor less than unity leads to reactive energy drawn from the supply, and rather than being converted to useful work, the reactive energy is wasted as heat generated in the system.

One of the methods of bringing the power factor back to unity or near to unity is the synchronous condenser, which when connected to the system, dynamically delivers the reactive power required as an uninterrupted reference source for improvement. The condenser adjusts the excitation level automatically and thereby maintains the power factor to the desired level. The synchronous condenser improves the overall power quality of a power system as it helps to reduce voltage transients, creates a more uniform sine waveform, and reduces the harmonic distortions in the system. All these advantages make the synchronous condenser a critical factor for any power facility.

In practice, the level of excitation of the synchronous condenser depends on the amount of power factor correction necessary and the level sensed by the controls of the condenser. The condenser then adjusts its excitations levels automatically for maintaining the power factor at the specified setting. The synchronous condenser adjusts the power factor without creating switching transients, and it remains unaffected by harmonic currents that the solid-state motor drives produce.

In contrast to conventional methods of power factor correction, using a synchronous condenser results in a much smoother waveform and does not affect a system adversely, when loaded with current harmonics. As the condenser is a low impedance source, it appears as inductive to loads.

Synchronous condensers are usually fitted with frequency, voltage, and temperature sensors that protect the system against overload and other dangerous situations. The solid-state voltage and power factor regulators within the synchronous condenser to a precision job, and switchboard grade meters keep track of the VAR and power factor. All this instrumentation makes sure the power supply system operates at its peak performance 24/7. To make it compatible to any industrial applications, manufacturers of synchronous condenser usually provide them with color touch screen displays and means of communicating remotely.

Synchronous condensers offer several advantages. These include elimination of power bill penalties, automatic power factor corrections, increased system stability, mitigation of voltage transients, reduction of system losses, and lowering the overall maintenance costs.

As synchronous condensers do not have to supply a torque, there is usually no output shaft. Enclosed in a leak-proof shell, the synchronous condenser is filled with hydrogen to help with reducing losses from wind friction and cooling. As hydrogen is lighter than air by about 7%, the wind friction or windage losses are reduced by 7% for a unit filled with hydrogen over that containing air. Additionally, heat removal improves by a factor of ten.

Raspberry Pi to Linux Desktop

You may have bought a new Single Board Computer (SBC), and by any chance, it is the ubiquitous Raspberry Pi (RBPi). You have probably had scores of projects lined up to try on the new RBPi, and you have enjoyed countless hours of fun and excitement on your SBC. After having exhausted all the listed projects, you are searching for newer projects to try on. Instead of allowing the RBPi to remain idle in a corner, why not turn it into a Linux desktop? At least, until another overwhelming project turns up.

An innovative set of accessories converts the RBPi into a fully featured Linux-based desktop computer. Everything is housed within an elegant enclosure. The new Pi Desktop, as the kit is called, comes from the largest manufacturer of the RBPi, Premier Farnell. The kit contains an add-on board with an mSATA interface along with an intelligent power controller with a real-time clock and battery. A USB adapter and a heat sink are also included within a box, along with spacers and screws.

Combining the RBPi with the Pi Desktop offers the user almost all functionalities one expects from a standard personal computer. You only have to purchase the solid-state drive and the RBPi Camera separately to complete the desktop computer, which has Bluetooth, Wi-Fi, and a power switch.

According to Premier Farnell, the system is highly robust when you use an SSD. Additionally, with the RBPi booting directly from an SSD, it ensures a faster startup.

Although several projects are available that transform the RBPi into a desktop, you should not be expecting the same level of performance from the RBPi as you would get from a high-end laptop. However, if you are willing to make a few compromises, it is possible to get quite some work done on a desktop powered with the RBPi.

Actually, the kit turns the RBPi into a stylish desktop computer with an elegant and simple solution within minutes. Unlike most other kits, the Pi Desktop eliminates a complex bundle of wires, and does not compromise on the choice of peripherals. You connect the display directly to the HDMI interface.

The added SSD enhances the capabilities of the RBPi. Apart from extending the memory capacity up to 1 TB, the RBPi can directly boot up from the SSD instead of the SD card. This leads to a pleasant surprise for the user, as the startup is much faster. Another feature is the built-in power switch, which allows the user to disconnect power from the RBPi, without having to disconnect it from the safe and intelligent power controller. You can simply turn the power off or on as you would on a laptop or desktop.

The stylish enclosure holds the add-on board containing the mSATA interface and has ample space to include the SDD. As the RBPi lacks an RTC, the included RTC in the kit takes care of the date and time on the display. The battery backup on the RTC keeps it running even when power to the kit has been turned off. There is also a heat sink to remove heat built-up within the enclosure.

Battery Monitoring with Comparators

So many portable consumer electronics gadgets in use today use small, button- or coin-cell batteries. Sometimes it is necessary to monitor their state-of-charge (SOC) and health efficiently without affecting their SOC significantly, but this can be a challenge. However, simple low-power monitoring circuits for small batteries using comparators can overcome this challenge.

Managing Batteries in Portable Systems

Usually, the system engineer budgets the system power requirements carefully during the system design. A micro-controller or microprocessor within the gadget is the actual brains that manages the system reliably and performs the required functions. Since it is typical for the controller to be power-hungry, as it is the workhorse of the system, there is not much sense in making the controller do all the work. To prevent unnecessary power dissipation, the controller is designed to remain asleep for extended periods, only waking up when flags are presented on the GPI pins.

Therefore, engineers resort to using low-power circuits for continually monitoring the vital functions of the system. When these circuits detect an event, they flag the micro, usually in the form of interrupts. The micro then wakes up to perform its required duty. One of the vital functions of such circuits is to monitor the state of the battery. When the battery voltage dips below the pre-defined threshold, it means it has discharged and requires charging. Likewise, as soon as the battery voltage crosses another pre-defined threshold, it means it is completely charged with no further requirement of further charging. Similarly, it is important to monitor the case temperature of the battery and the ambient temperature, as this provides much information about the loading conditions on the battery, and the presence of a fault.

Using Comparators for Monitoring

Although there are sophisticated battery monitors with fuel gauges, and monitoring battery voltage and temperature with an analog-to-digital converter is possible, these essentially require careful tradeoffs with portable gadgets. A designer must consider form factor, cost, accuracy, speed, and power consumption when creating the design, as different systems may have different priorities.

It is possible to have a simple comparator monitoring the voltage at the battery terminals. For a fully charged battery, the output voltage of the comparator transitions from high to low and from low to high for indicating a fully discharged battery. When implemented with external hysteresis, thresholds can be pre-defined to yield the proper output states.

The comparators can be tiny-footprint devices with internal references, consuming very low quiescent currents. When large-value resistors are used in the circuit, the overall operating current will be comparable to the typical self-discharge rate of the battery. By designing the circuit to operate from a low supply voltage of about 1.7 V and consuming less than 2 µA of current, the circuit will be able to produce the proper output state even when the battery has only a minimum charge remaining.

The component values necessary to realize the application for battery state monitoring must be selected with care. The determined threshold value should provide a narrow band of hysteresis to allow for more cushion for component variation and tolerances. Using resistors with 0.5% makes the circuit work with ±1% accuracy.

Measuring Very High Currents

High currents, such as 500 Amps and above, are common nowadays. Industries regularly use equipment consuming high currents, and vehicle batteries experience very high currents for a short time during starting. With vehicles increasingly trending towards their electric versions, it is becoming necessary to be able to measure high currents with precision. Increasingly, it is increasingly becoming critical to monitor current consumed accurately for ensuring performance and long-term reliability.

Current sensing is necessary for essential operations such as battery monitoring, DC to DC converters, motor control, and so on. Device specification mainly defines the performance of any current sensor solution. This includes the efficiency, precision, linearity, bandwidth, or accuracy. However, for designers designing a system to satisfy all the requirements of the specifications can be a challenging task. One way to do this is to use a precision shunt, a shunt monitor, and a signal conditioner.

The ±500 A precision shunt-based current sensor design from Texas Instruments (TI) has an accuracy of 0.2% of full scale reading (FSR) over a huge temperature range of -40 to +125°C. Several applications such as motors and battery management systems require such precision current sensing. In general, these applications suffer from poor accuracy caused by shunt tolerances, temperature drift, and non-linearity. Shunt monitors such as INA240, and signal conditioners such as PGA400-Q1 from TI help to solve these problems.

The design from TI works on 48 V or 12 V battery management systems and is suitable for measuring ±500 A, with both high- and low-side current sensing. It accurately compensates for temperature and non-linearity to the second order with an algorithm. Furthermore, it offers protection against harness faults such as input/out signal protection, reverse polarity, and overvoltage. TI has protected its design from electromagnetic interference.

Several ways of measuring currents are available, and these include using magnetic saturation, magneto-resistance methods, Lorentz force law, Ohm’s law, Faraday’s induction law, and more. While each technology presents its own advantages and disadvantages, every customer has his or her own preference and place of use for the specific topology they prefer to choose.

The simplest and most common technology makes use of Ohm’s law, which this TI design also uses. When designing the system for measuring currents, essentially the designer must choose where the current is to be measured—high side or low side, the range of measurement, and whether the current is uni-polar or bi-directional. These parameters define the suitable topology and the design the designer must use. Most vehicle systems now prefer to use 48 V and this new trend implies the current sensor will have to measure a large span of range.

The method of measurement follows a simple process. The ±500 A current passes through the shunt whose resistance measure 100 µΩ. This causes a noticeable amount of voltage drop across the shunt. The current sense monitor INA240 measures this small amount of voltage and passes it on to the signal conditioner, PGA400-Q1. The delta-sigma ADC micro-controller inside PGA400-Q1 creates a ratio-metric voltage between 0.5 and 4.5 V using its linearity and compensation algorithms.

Let the Raspberry Pi Monitor Energy

If you are looking for monitoring energy remotely, an open source system that uses the ever-popular single board computer, the Raspberry Pi (RBPi) may be suitable. The company, OpenEnergyMonitor, makes the open-source tools for monitoring energy, and at present, they are using the RBPi3. According to their co-founder Glyn Hudson, the aim of OpenEnergyMonitor is to help people understand and relate to how they use energy from their energy systems, and the challenges of sustainable energy.

The system uses five main units. Users can assemble and configure these to work in a variety of applications. Both hardware and software in the system is fully open-source, and the hardware is based on Arduino and RBPi platforms. Users can opt to use the system for monitoring home energy, monitoring solar PV, and or monitoring temperature and humidity.

emonPi

When configuring the OpenEnergyMonitor system, emonPi, as a simple home energy monitoring system, it allows measuring the daily energy consumption and analyzing real-time power use. The all-in-one energy-monitoring unit, emonPi is a simple installation based on the RBPi, requiring only an Ethernet or Wi-Fi connection at the meter location.

Clip-on CT sensors on the emonPi enable it to monitor independently two single-phase AC circuits simultaneously. While the emonPi can monitor temperature, it has an optical pulse sensor to interface directly with the utility meters, which means the emonPi has to be installed next to the utility meter.

The emonPi comes with Emoncms, the open-source web application. This helps in logging and visualizing energy use along with other environmental data such as temperature and humidity. It has two power outlets and requires Ethernet or Wi-Fi to transfer data. The RBPi operates on a pre-built OS on an SD card included with the energy monitor. The 5 VDC power required has to be fed in from an external power supply unit.

As power is the product of voltage and current, the emonPi requires an AC-AC voltage sensor adaptor and a clip-on CT sensor. While the emonPi comes with one CT sensor as standard, it can accept two CT sensors.

emonTx

For remote monitoring, users can use emonTx, a remote sensor node as an alternative to emonPi. The emonTx runs as a standalone unit, with an ESP8266 Wi-Fi module running EmonESP. This can post directly to Emoncms without using emonPi or emonBase.

Users can monitor a maximum of four single-phase AC circuits with the clip-on CT sensors using the emonTx. A plug-in AC-AC adaptor powers the unit, and provides the AC voltage sample, which the emonTx uses for real-time power calculations. If AC power is not available, emonTx can be powered using four AA type batteries.

Optional LED Pulse Sensor for Utility Meter

This sensor allows interfacing directly with utility meters that have LED pulse output. It is compatible with emonTx and emonPi, and reports the exact amount of energy as the utility meter does. Although best used together with clip-on CT sensors, the LED pulse sensor cannot measure instantaneous power.

emonBase

This is a web-connected gateway, consisting of an RBPi and RFM69Pi RF receiver board. It receives data via a low power RF carrier at 433 MHz from emonTx or emonTH and offers local and remote data logging using Emoncms.

Are Pin and Sleeve Connectors Better?

Most people in the US are familiar with the twist lock cable connectors, as these are the NEMA standard. In Europe, there is another advanced cable connector—the pin and sleeve connector—but it is not so very well known in the United States.

In short, pin and sleeve connectors deliver power through sealed connections, while insulating the connections from moisture, grime, and chemicals, which makes them suitable for applications under abusive environments. Their design is such as to prevent them from being disconnected under load. Pin and sleeve devices come in varying designs, ranging from metal-housed types to high impact-resistant plastic ones.

Whether specifying mobile power solutions on the factory floor, designing machines for international customers, or planning outdoor power distribution systems, pin and sleeve connectors with mechanical interlock switches are a cost-effective and safe option to all wiring requirements.

Well-suited for supplying power, these male-female connections can deliver power to a wide range of equipment such as lighting, portable tools, conveyors, compressors, motor generator sets, and welders. They are also good for matching the right equipment with high-current power sources, while integrating fused and switched interlocking receptacles in wet or corrosive environments.

When compared to the standard twist lock, pin and sleeve connectors offer plenty of other benefits. While their click-lock housing makes assembly fast and easy, their rugged design makes them highly durable. In contrast to male NEMA plugs leaving their pins exposed to the environment, a shroud surrounds the male plugs of a pin and sleeve connector and protects the contact pins.

With more configuration options for pin and sleeve connectors in the market than available for twist lock, they are color-coded to different amps, from 20 to 100 in the US. On the other hand, there is no color-coding for NEMA twist lock sockets.

Whereas twist lock sockets offer IP protection only as an option and with a higher price, this is a standard feature of the pin and sleeve connectors. While twist lock sockets are available only in the markets of North America, options of North American along with International versions are common for the pin and sleeve connectors.

Conforming to IEC 60309, one of the most appealing reasons for using the pin and sleeve connector is their built-in safety features, designed to make the connectors safe for both, the operators and the application.

IEC 60309 focuses on operator safety for a family of connectors for use in equipment in domestic as well as international markets. Products intended to be compliant with IEC 60309 must meet global standards, regardless of the origin country or the manufacturer. The standard specifies five devices—mechanical interlock switch receptacles, inlets, receptacles, connectors, and plugs.

Every pin and sleeve design is unique with respect to the design voltage. That means there is no possibility that a wrong voltage will be accidentally used in the application. Moreover, the design of plugs prevents them from being inserted into the wrong outlet type.

An additional safety feature is the pilot pin included in the electrical interlock systems. The pilot pin contact disconnects before all other connections do, signaling the electrical interlock to shut off the power.