Monthly Archives: October 2016

Rectannas : Will They Make Solar Cells Obsolete?

Professor Baratunda Cola and colleagues at the Georgia Institute of Technology, Atlanta, claims to have improved on the solar cells available. They have reported their findings in Nature Nanotechnology. The new type of solar cell is actually a rectenna – half antenna and half rectifier that can be tuned to any frequency as a detector, while generating electricity from solar and infrared light falling on it.

The team claims they can achieve a broad-spectrum efficiency of 40 percent with their new cell, although the efficiency they have achieved so far is only one percent. Comparatively, conventional solar cells such as the silicon and multi-junction gallium arsenide types have a maximum efficiency of 20 percent. The team also claims their rectenna can achieve an upper limit of 90 percent efficiency for single wavelength conversion at only a one-tenth the cost of conventional solar cells.

The theory of rectennas is not new, but was discovered more than 50 years ago. However, so far, technology was not advanced enough to fabricate them. According to Professor Baratunda Cola, with currently available technology, it is now possible to make cheap solar-to-electricity converters from carbon nanotubes with ends turned into a special tunnel diode. Cola says the concept is well suited for mass production.

Rectennas are made by growing fields of vertical carbon nanotubes. Their length roughly matches the wavelength of the energy source – for solar radiation, it is one micron. An insulating dielectric such as aluminum oxide caps the carbon nanotubes on the tethered end of the bundles. On the dielectric grows a low-work function of metal – calcium/aluminum. This arrangement makes each nanotube a rectenna with a two electron-volt potential when collecting sunlight and converting it to direct current.

According to Cola, the process uses three steps. In the first step, they grow a large array of vertical nanotube bundles. Then one end of the tubes is coated with a dielectric, while a layer of metal is deposited. One end of the nanotubes changes to a super-fast metal-insulator-metal type of tunnel diode by this process. This method is eminently suitable for mass production, and up to ten times cheaper than making crystalline silicon cells.

With its metal-insulator-metal form, the structure resembles a capacitor with a rating of a few attofarads (1aF = 10-18F). Each nanotube bundle is only 10-20 microns in diameter and consequently, the area of the capacitor plates is so small that the electrical field concentration at the end of the nanotube is very high. With the low work function of the metal, the device behaves just as a tunnel diode does in the peta-hertz (1015 Hertz) region when excited by solar energy and emits electrons in bursts of femtoseconds (10-15 seconds).

Commercialization will require several trillions of nanotube bundles growing side-by-side. Once optimized for higher efficiency, this bunch of nanotube bundles could ramp the power output well into the megawatt range. According to Cola, increasing the efficiency can be achieved by lowering the contact resistance between the antenna and diode. The team expects to improve the efficiency up to 40 percent in only a few years.

Controlling RGB LEDs via the Raspberry Pi

Digital gates are great for switching LEDs on or off. Micro-controllers are even better and so are single board computers. That is because they contain several gates to control the LEDs. To top it all, you can program single board computers such as the RBPi or Raspberry Pi to control several LEDs individually to run at different on/off cycles. Additionally, multiple color LEDs are available, such as RGB LEDs, with which you can generate any combination of the basic red, green and blue colors.

Although the GPIO pins of the RBPi can switch on an LED, the pins cannot supply beyond their limit. Therefore, when driving LEDs from the GPIO pins, a current limiting resistor is necessary in series with the LED, to prevent the IO pin from being damaged. The resistance value will depend on how much current the IO pin can source or sink, and the supply voltage of the RBPi or LED.

The RBPi has a 40-pin GPIO header among which, you can control several pins through software. The most common use of external circuits and LEDs with GPIO pins is to indicate status visually. For example, you may be controlling a remote circuit with software, and an LED nearby can indicate its status. The LED lights up to indicate the remote circuit is powered.

It is a good thing that human eyes have something called the persistence of vision. When we see something, its image persists in our eyes for a brief time. Therefore, we can see flashing lights only when they are flashing relatively slowly. Beyond a certain speed, our eyes cannot make out the individual flashes and the flashing light looks as if it is steadily lit. Using a technique called PWM or Pulse-Width Modulation, and controlling the on time of a GPIO pin through software, we can make an RBPi drive an LED such that it looks as if the LED is breathing. Doing the same with an RGB LED, the RBPi can cycle the lights to produce any color in the rainbow.

You can build a simple RGB LED board with a single bright RGB LED, three current limiting resisters and a four-pin connector on a prototype PCB. RGB LEDs have four pins and come in two configurations, common cathode and common anode. In the common cathode configuration, the package combines the cathodes of all the three LEDs into a single pin with the anodes individually available. For the common anode configuration, all the three anodes are combined into one pin, while the cathodes are individually accessible.

To drive an RGB LED you will need to connect its individual anodes or cathodes to three GPIO pins through current limiting resistors. If you use a common anode RGB LED, you will have to connect its common anode to a supply voltage. For a common cathode RGB LED, you will need to ground its common cathode. Now, you can switch on an individual LED of the combination by switching on the corresponding IO pin. See this tutorial for writing simple Python scripts for controlling the LEDs via the RBPi.

How To Compensate Cable Voltage Droops?

Not only ordinary wires, but also USB cables can cause voltages to droop. This is evident if you have used an extra long USB cable and found that the device you were charging, such as your phone or tablet, was taking an extra long time to charge. The reason is the excessive voltage drop across the long USB or Universal Serial Bus cable.

Most chargers come with overcurrent protection. That means when the charging current exceeds a certain limit, the charger reduces its output voltage to prevent the charger from burning up. Moreover, when the charging current is high, the cable resistance causes the voltage at the device end to droop, increasing the charging time considerably. Since resistance increases with cable length, the voltage drop is also more with a longer cable. Hence, cable voltage droop has a negative impact on the operation of the system.

Proper charging and time taken is a critical design parameter for a device under load. With system load located at a distance from the output of the power supply, the absence of remote sensing may cause the voltage seen by the load to be significantly lower than desired. Contribution to the voltage droop is from thin circuit board traces, connector interface and cabling resistance. The situation gets worse when load currents are higher, decreasing the operational voltage at the load and causing possible erratic circuit operation.

A typical USB cable uses four wires of 24AWG each about a meter long and has a contact resistance of about 30 milliohms per contact. As a USB cable used for power transfer uses four connections (two on each cable end), the total contact resistance is 120 milliohms. The two one-meter wires of 24AWG have a total resistance of 166 milliohms. That makes the overall resistance of the USB cable to be 286 milliohms.

Typical converters are designed to supply a maximum output current of 2.1A. That means the voltage drop across the cable would be 0.6V when it is supplying maximum current. The voltage expected at the end of the cable would drop to 4.4V for a 5V set-voltage converter. This is much lower than the maximum lower-limit of most loads working at 5V and this may lead to potential issues with high-current loads.

Designers overcome this voltage drop by increasing the output voltage at the source. Instead of the fixed 5V, the converter would generate 5.6V, which after the 0.6V drop would present the necessary 5V to the load. They do this by monitoring the load current by adding a sense resistor in the path of the output current. A differential operational amplifier amplifies the voltage across the sense resistor and this voltage causes the output voltage to increase with increasing load.

As the load current increases, so does the output voltage of the converter. However, at the end of the cable, the compensated voltage is nearly a constant figure, representing a well-regulated voltage.

Compensating the output prevents the voltage at the load from drooping. This avoids potential system issues such as power cycling, latch-up conditions or decreased system performances.

Android vs. Linux – Which OS is better?

Is Android A Better OS Than Linux?

Android has established itself as an important operating system for mobile devices. Google developed Android as an open source OS based on the Linux kernel. Google selected the Linux kernel because of its proven driver model, existing drivers, process and memory management, networking support and several other core operating system services. However, the Google team had to make several changes to make Android capable of operating mobile devices successfully. Differences with standard Linux are highlighted here.

The target architecture

Although the Linux kernel supports several architectures, right now, Android supports only two: ARM and x86. The ARM platform is more prevalent on mobile phones while the Android-x86 targets mainly the Mobile Internet Devices or MIDs used for general-purpose desktop/laptop/server computing systems. This being the fundamental difference between the two Operating Systems, it provides a strong insight into further divergence between the two.

Modifications in the kernel

Android does not use the standard Linux kernel straightaway, but uses it with some enhancements. These include alarm driver, shared memory driver, inter-process communication interface, power management, low memory killer, kernel debugger and logger. Google has contributed all the kernel enhancements back to the open source community under GPL.

Bionic C library

The GNU C library used by most Linux distributions makes use of the Native POSIX Thread Library or NPTL, which offers high performance, especially in server applications. However, disk space footprint and memory requirements of NPTL are far too large for resource-limited systems such as mobile devices.

This led Google to create a new C library called Bionic. It has fast execution paths, avoids edge cases and remains a simple implementation. As mobile devices are single user systems, for security reasons Google has removed the settings for groups and passwords, keeping only a unique user id and group id. Bionic operates with the limited CPU and memory resources available on Android platforms.

The Dalvik Virtual Machine

Android uses a virtual machine to run applications. Most top cell manufacturers such as Samsung, Motorola and Nokia use J2ME, a mobile optimized version of the Java virtual machine. In contrast, Android uses the Dalvik Virtual Machine, which is a standard Java platform. The dex files used by Dalvik are more compact and optimized to perform well on mobile devices with slow CPUs, limited memory, no swap space and limited battery power.

File system

Most desktop/laptop/server applications use magnetic hard disks, which the standard Linux systems manage with the latest Ext journaling file system. However, magnetic drives are physically too large, too fragile and consume too much power. To provide a robust file system, embedded systems use solid-state memory devices such as NOR for code execution and NAND for storage. Block erasure and memory are important features of solid-state memory, which the Ext file system does not handle. Therefore, Android uses an optimized Linux flash file system called YAFFS and this deals with lifetime limitations, bad block management and error correction for maintaining data integrity in NAND flash systems.

Power management

Standard Linux systems manage power though APM or ACPI. Android does not use either, relying more on its own PowerManager module, which is a Linux power extension. The module has low-level drivers for controlling the peripheral supported such as screen display and backlight, keyboard backlight and button backlight.

The Raspberry Pi Sense HAT

If you are targeting the Astro Pi mission, it makes sense to get the Sense HAT as an add-on board for your tiny single board computer, the Raspberry Pi or the RBPi. With a fantastic RGB LED matrix, not only is the board beautiful to look at, but it also comes with a plethora of sensors on-board. That makes it useful for the applications in the International Space Station where it is headed to in December 2015.

The Sense HAT looks like an ordinary board with an 8×8 RGB LED matrix on it. You can use it to display graphical information in color. For example, using the display you can indicate geomagnetic North. Apart from the matrix, the Sense HAT also has a five-button joystick, which allows the user to interact with the programs the RBPi is running. That includes playing games such as Tetris, Snake or Pong on the RBPi.

The Sense HAT includes several sensors such as a gyroscope, accelerometer and magnetometer. It also has sensors to read ambient temperature, barometric pressure and humidity. A Python software library that comes with the board provides the user with an easy access to everything on the Sense HAT.

Using the software library, you can conduct a huge range of projects for the Sense HAT and RBPi combination. For instance, if you are traveling with the combination, it can measure and show your speed. At the same time, it can tell you the direction it is facing, how humid is the atmosphere nearby and even the temperature of your surroundings.

The Sense HAT kit comes with the fully assembled Sense HAT board, four mounting posts and eight screws so you can mount the HAT on your RBPi securely. Mounting the board on the RBPi is simple. First, fit the four mounting posts with four screws on the board. Now, align the 40-pin connector on the HAT to fit on to the GPIO connector of the RBPi and push in firmly. The four posts will align with the mounting holes of the RBPi. Secure those with the remaining four screws and you are done.

To install the software, visit the AstroPi and the Swag websites. Here, you can find out of the world projects, a host of ideas and instructions related to the RBPi and the Sense HAT, fit for the applications on the ISS or the International Space Station.

Technical specifications of the Sense HAT are impressive, considering the inexpensive setup. The Gyroscope measures angular rate at +/- 245/500/2000 dps. The Accelerometer measures linear acceleration at +/- 2/4/8/16 g. Temperature accuracy measured in the 0-65°C range is +/- 2°C. The Relative Humidity sensor has an accuracy of +/- 4.5% within the 20-80%RH range, with a temperature accuracy of +/- 0.5°C in the 15-40°C range.

You must take care while measuring temperature with the Sense HAT. When the LEDs are lit for some time, they, together with the board, tend to get warm. That heats up the air nearby and the measurement may not reflect the ambient temperature accurately.

Differential Pressure with a Tiny Sensor

Process control requires system operators to monitor and control the condition and movement of liquids and gases. Several instruments are available for this, allowing measurement and monitoring of variables, and these fall under the categories of pressure, temperature, level, and flow. Among the pressure-gage category, differential-pressure gages receive the widest recognition for being the largest specialty type – useful in filtration, flow, and level measurements.

While standard pressure gages measure pressure at a single point in a system, differential pressure gages measure pressures at two points and display the difference on a single dial. This makes it easy for the operator to know at a glance, which of the two points is at a higher pressure, and by how much. Use of differential pressure gages greatly reduces operator error, protecting expensive equipment. They reduce operator training and maintenance time, thereby improving process efficiency.

For instance, differential pressure gages are popularly applied in filtration. In this process, a filter separates unwanted contaminants or particles from a gas or liquid system. However, with the progress of the process, the filter becomes increasingly clogged, leading to a drop in efficiency and pressure at the outlet.

It would seem enough to use a single standard pressure gage at the outlet to monitor the health of the filter and assess the time for its inspection and replacement. However, the situation is complicated, as most processes do not maintain a steady working pressure. Several factors are responsible for this, such as compressor or pump on-off cycles or valve open-close cycles, causing wide pressure fluctuations in most processes. For many systems, operators expect such fluctuations of pressure as normal, within limits.

Using two standard pressure gages, one at the input and the other at the output, introduces two additional problems for the operator. First, this compounds the accuracy errors resulting from the two gages as against error from one gage. Second, the operator needs training in reading the two gages, then subtracting the readings, and finally, interpreting the result. History shows many operators do not truly understand the importance of the calculation.

Installing one differential pressure gage using the same taps at the filter inlet and outlet solves all the problems listed above. The accuracy goes up as the rate of error drops. Additionally, the operator does not have to rely on mathematics to understand and interpret the reading – most differential pressure gage dials feature a red arc to indicate the clogging of the filter.

The SDP3x differential pressure sensor from Sensirion is a tiny device. Its dimensions are only 5x8x5 mm, making it one of the smallest of its kind, but with countless new possibilities of applications. It is well suited for use in portable medical devices as well as in consumer electronics.

Users can choose between an analog signal output and a digital one from two versions of the fully calibrated and temperature-compensated differential pressure sensor. The digital sensor, the SDP31, comes with an I2C interface, while the analog sensor, the SDP36, offers an analog output signal. The sensors have a sampling rate of 2 KHz with a resolution of 16-bits, and a measurement range of +/-500 Pa with a span accuracy of 3% of the reading.

Create a Baby Monitor with the Raspberry Pi

The arrival of a baby nearly always alters the entire timetable for all the members of the family, whether willingly or otherwise. For the parents, if they are first timers, the joy of seeing the tiny human is never-ending – they want to see the baby even if they are away from home. That is where a baby monitor comes in and what better to use for the project other than the versatile single board computer, the Raspberry Pi or RBPi.

As a simple, cheap, and low power computer, the RBPi works as a perfect fit for a baby monitor that has a motion detector and a simple web browser interface. That allows you to see the little one on your phone or laptop any time you want.

You will need the entire RBPi kit for this project. The kit will have the RBPi, its SD Card, the USB charger, and the micro USB cable. Additionally, you will need a USB webcam, an Ethernet cable, and a Wi-Fi dongle or an Ethernet power line adapter. Although not part of the project, you will also need a laptop or a desktop to prepare the SD Card for the RBPi. To interact with the RBPi, you will also need a keyboard, mouse, and a monitor.

From the official site of the Raspberry Pi, download the latest Raspbian image on your laptop. Now transfer the image to your SD card, making sure you have backed up anything important on the SD card beforehand. Writing an image wipes off whatever you have on your SD card, so be careful. If this is complicated for you, pre-pared SD cards are also available. Insert the SD card into the slot on your RBPi, plug in the keyboard, mouse, monitor, and the Ethernet adapter and power up the RBPi.

If you do not have a keyboard, mouse, and monitor for your RBPi, you can still connect to it using your laptop. If you are using Linux or Mac on your laptop, connect using SSH. For Windows, you can use Putty. Once you have powered on the RBPi, there will be only a few LEDs blinking, but nothing else. That is why it makes such a good baby monitor – it is silent.

To connect to the RBPi, you will need to know its IP address. As the RBPi is connected to the Ethernet adapter, your router will be the best place to look – search in the connected devices, and make a note of the IP address. Now, to connect via SSH, issue the command from your laptop: ssh pi@xxx.xxx.x.x, where the xx denote the IP address you noted down from the router. When prompted for a password, enter raspberry, as this is the default.

Update and upgrade your OS to ensure you have all the updates and security patches. Now, install motion, as this is the package to allow you to monitor the baby with the webcam. Configure motion to operate in daemon mode with a low frame rate, and start it working with the command: sudo service motion start. Now browse to the webcam from your laptop with: http://xxx.xxx.x.x:8081.

Using OpenHAB with a Raspberry Pi

Nowadays it is common to have smart home products that you can remotely command to control, adjust, and to switch on and off. The single board computer, Raspberry Pi or RBPi is suitable for building a touchscreen command center to interface with such smart products and to provide a suitable interface for control and task scheduling. As an introduction, the project will consist of a Wi-Fi enabled RGB LED strip. It will interface with an RBPi running OpenHAB. This will allow wireless control to switch the LED strip on or off from a smartphone or any other computer on the network.

With OpenHAB, you can interface with over 150 different existing smart home products. Moreover, OpenHAB is very flexible, is open source, and is free to use. Although you can use OpenHAB on an RBPi, it can easily run on any platform – Linux, OS X, or Windows. That means the same setup can be run from any old laptop or desktop you may have lying around.

For this project, the main components you will need are an RBPi and its touchscreen. An RBPi2 is recommended and you can use the 7-inch Raspberry Pi Foundation touchscreen. Some of the additional things you will need are a microSD card, a USB Wi-Fi dongle, a power supply for the RBPi, the NeoPixel LED strip starter pack, a logic level shifter, an ADAfruit HUZZAM ESP8266, and some hookup wire.

To begin, assemble the screen to the RBPi. This can be somewhat tricky if you do not have instructions. There will be two flat ribbon cables, a large one for the display, and a smaller one for the touchscreen. The large cable from the display connects to the display controller board, and the smaller cable from the display controller board connects to the display. Once this is done, you can screw the display controller board with the RBPi on its back on to the standoffs on the back of the screen. The ribbon cable from the controller board connects to the display connector on the RBPi. Power to the display comes from the GPIO pins on the RBPi, for which you need to connect the 5 V and the GND pins via two jumper wires of red and black color, respectively.

Flash the microSD card with the latest build of Raspbian from the Raspberry Pi website and boot up the RBPi with it. You can now connect your keyboard, mouse, and the Wi-Fi adapter. Configure the RBPi to connect to your Wi-Fi network and get the touchscreen to work. For this, you may need to update and upgrade your OS.

The next step is to install the home automation control software, OpenHAB, and its add-ons – follow the instructions here. Next, solder the logic level converter between the ESP8266 and the NeoPixel LED strip. This is necessary, as the strip works on 5 V, whereas its controller, the ESP8266 works on 3.3 V. Make sure the logic level converter is connected the right way. After this, you will need to flash the ESP8266 with the Arduino IDE.

Now, you can download and install the OpenHAB app on to your phone and set it up to control the RBPi on its IP address.

What is Geomagnetic Indoor Positioning?

Thanks to Google and our smartphones, almost all users are aware of GPS or global positioning systems. With GPS, we can locate our position on a map displayed on our smartphones with an accuracy of about 200 m. This technology serves us well while traveling – when we have to reach a destination from our present location or when finding the best route between two locations. However, GPS is not a very suitable technology for either indoor use or when the smartphone is offline.

For instance, it is not easy to navigate successfully through a large shopping mall, a superstore, or an airport unless there are way-finding directions available. In fact, marketing research has pointed out that stores lose considerable business (nearly 15%) because customers are unable to locate their required products in the stores. In the US, customers spend about $500 billion annually, on personal care, groceries, and various sundries. Over time, adoption of indoor location and related initiatives could influence this indoor market by well over $10 billion.

Therefore, there are over several startups competing for attention in the emergent arena of indoor location and proximity marketing. Additionally, there are multiple technologies for bringing offline analytics and indoor location to malls, stores, sports stadiums and other venues. Although these technologies include LED lighting, inaudible sound waves, Bluetooth beacons, Wi-Fi, and Cameras, magnetic positioning leads the way.

All other technologies need installation of additional hardware and hence, involve additional expenses. In comparison, magnetic positioning makes use of the Earth’s magnetic field to enable the compass in the user’s smartphone to locate the individual precisely within indoor spaces. It does not require additional hardware and is compatible with almost all smartphones.

In nature, animals make use of the Earth’s magnetic field to locate themselves in relation to their destination. That is how migratory birds and fish return to their breeding grounds every year even when they are thousands of kilometers away. Smartphones are similarly capable of detecting and responding to magnetic field variations inside buildings.

According to IndoorAtlas, promoting and deploying magnetic positioning, each building or structure, with its reinforced concrete and steel structures, presents a unique magnetic fingerprint. This is based on the way the materials of the building affect and distort the Earth’s magnetic field. Once these patterns are precisely assigned to a building floor plan, users of smartphones can be located accurately inside indoor spaces such as airports, malls, hospitals, and retail stores. In short, this is like indoor GPS, and much more precise.

In comparison to GPS, geomagnetic indoor positioning is capable of 1-2 m accuracies in indoor environments. According to IndoorAtlas, mapping an area of roughly 25,000 square feet requires an hour to offer six-feet accuracy through sensors streaming data into a cloud storage. As a store or building interior is remodeled or changed in any way, the indoor maps are updated automatically using the sensor data.

Apart from tracking shopper location, geomagnetic indoor positioning offers direct blue-dot navigation to an area of product on the shelf or in an aisle. Therefore, customers are able to locate their desired products, bringing immediate benefits to the retailers.

What is the IEC 61800-5-1 Safety Standard?

Almost all industrial applications require using electric motors in some form. You can see them being used in factory robotics, compressors, blowers, cooling and recirculating pumps, lifts, hoists, mixers, cranes, paper mills, printing presses, conveyor belts, fans and in many other applications. Worldwide, over a 300 million electric motors are in use, and their numbers are growing steadily every year.

When dealing with adjustable-speed electric power-drive systems, it is necessary to isolate the low-voltage control system from the actual motor as it most often runs on a higher voltage. Such smart motor-control systems have other names also, such as AC motor drives or variable-frequency drives. Instead of running the motor at a fixed speed or using mechanical elements to control it, smart control systems employ sophisticated power electronics to control the speed, torque, and position of a motor. Adjustable speed drives improve the efficiency and controlling of motor drive systems substantially, and therefore, are widely used in motor drive applications.

The IEC 61800-5-1 is a safety standard specified by the International Electrotechnical Commission for adjustable-speed electrical power drive systems. It covers the safety aspects related to electrical, thermal and energy. In the part covering electrical safety, the standard defines requirements for ensuring proper insulation between circuits carrying voltages higher than 50 V and any drive system connectors or parts that humans may be able to access. What this means is any part of the system that a person can touch – motor, panel, switch, connector, cable, etc. – must be adequately insulated, if it is carrying a voltage higher than 50 V.

Most adjustable-speed electrical power drives use isolators as one of their key electronic components. For instance, by employing isolated gate drives, isolators control the turning On/Off the power transistors such as MOSFETs or metal-oxide semiconductor field-effect transistors used in the power stages. In addition, there are isolated ADCs or analog-to-digital converters and isolated amplifiers to convey voltage and current feedback from the high-voltage inverter output to the low-voltage control system. Moreover, power drives also need general-purpose communication links, where isolators transfer information from high-voltage circuits to earthed circuits. In this capacity, isolators also act as insulators.

An adjustable speed motor drive system has a grid input, which is typically a three-phase AC power supply typically at 400 V, 690 V, or 830 V at frequencies of 50 or 60 Hz. This is followed by a rectifier stage that converts the AC voltage into DC, filtered by high-voltage DC capacitors. A three-phase inverter usually follows, made up of IGBT, insulated gate bipolar transistor modules. IGBTs have isolated gates through which gate drivers provide the necessary drive voltages to turn the IGBT on and off. The control system uses a closed-loop and receives feedbacks through isolated voltage and current sense elements.

To conform to the IEC 61800-5-1 safety standard, the designer of a motor drive system needs to understand a few definitions such as creepage, clearance, system voltage, working voltage, and overvoltage category. Most industrial motor drives fall under Category-III, as equipment is connected permanently to supply mains, downstream of the distribution board.