Monthly Archives: October 2018

Which are Better – Round Cables or Flat Cables?

Both types of cables are available in the market—round ones and flats, and people use them according to the requirements of the application. As round cables were the first to arrive on the market, the industry has been using them as standard for long, in applications ranging from renewable energy to automation and manufacturing in general.

Flat cables arrived late on the scene, and offer a niche solution presently. However, they are gaining ground steadily for applications within the civil-aircraft markets, semiconductor industry, medical field, and for supplying data and power to machines. Flat cables are also called festoon cables, and the overhead crane companies actively use them for applications where winding cables around spools is difficult.

Comparison of Electrical Performance

The protection for internal EMI depends heavily on the construction of the cable. In general, flat cables do not transfer data very well. Individual shielded pairs within flat cables are necessary to provide coupling and crosstalk protection from pair to pair.

Most shielding materials to not hold a flat format and tends to become round. This makes it difficult to place a shield on the flat cable overall. This also makes it difficult to protect and shield a flat cable from the effects of external EMI. The naturally round shielding tendency provides greater protection against influences of external EMI on round cables.

The length of a cable, its quality of insulation, and the resistance of its conductors determines the voltage drop or attenuation on a power cable and this is immaterial whether the cable is round or flat. In both cases, higher quality of insulation and proper positioning of the ground wire improves the attenuation. Certain industries demand very high-performance (low attenuation and crosstalk) flat cables. With proper shielding, it is possible to transmit both power and signals through the same cable.

Comparison of Mechanical Performance

Cables in the industry face mechanical stresses of four main types—S-bend, rolling flex, tic-toc, and torsion. The natural capability of being able to move in multiple axes at the same time makes round cables capable of withstanding all the stresses. For instance, round cables can flex 30 million times in certain applications. On the other hand, flat cables can withstand only rolling flex, as the movement is only in one linear axis.

Movements in several axes such as during torsion can lead to flat cables binding, or twisting beyond a certain point. When under torsional loads, flat cables can spool and twist over a certain length. Preventing this requires every component of a flat cable to be integrated at the right position and twist. It also requires the cable to be embedded or wrapped with a PTFE (Teflon) tape for minimizing the frictional forces during torsion.

Summary

Round cables can maximally utilize the space inside the smallest required cross-sectional area. Drilling a round hole is easier than cutting a rectangle. Therefore, most machine or panel openings use round cables where using a flat cable may be more difficult, as it has an elongated cross-section. However, it is possible to stack flat cables to make them fit together in a smaller space than it is with round cables.

What is an Instantly Rechargeable Battery?

The batteries required to power them have so far impeded advancement of electric cars. A primary difference between vehicles powered by fossil fuels and those powered by batteries is that batteries tend to discharge with use and require a finite time to recharge, immobilizing the vehicle for that period. On the other hand, simply filling up the gas-tank with fossil fuel is enough to keep the car rolling on the road. However, that may be changing now.

Research at the Purdue University has led to the development of a new type of battery that can be recharged instantly. The new battery is also affordable, safe, and environmentally friendly. Presently, the viability of electric vehicles hinges on the availability of charging ports in convenient locations. However, the new battery technology allows drivers of hybrid and electric vehicles to charge up very quickly and easily similar to what the drivers of conventional cars do at a gas station.

This breakthrough will definitely boost the switching to electric cars. Not only does the new technology make it more convenient to drive electric cars, but it also reduces substantially the total infrastructure necessary for charging electric cars. Researchers, both professors and doctoral students, from the Purdue University have co-founded IF-Battery LLC for developing and commercializing the technology.

The new battery is a flow type and does not require to be charged at an electric charging station—it is enough to replace the fluid electrolyte of the battery. This is very similar to filling up the gas tank. The fluids from the spent battery can be collected and recharged at any hydroelectric, wind, or solar plant. Therefore, when an electric car using this new battery arrives at the refueling station, the driver can simply deposit the spent fluids for recharging, while filling up his or her battery with new fluids just as he or she might fill gas in a traditional car.

The difference between this flow battery and those developed earlier so far is this new battery does not have any membrane. The membranes other flow batteries use are expensive and vulnerable to fouling. Not only does membrane-fouling limit the number of recharge cycles of the battery, but can also contribute to a fire. Components used in the IF-Battery are safe to store in a family home, and are stable enough so major production and distribution centers can use them, and are cost effective.

In place of building several charging stations, it would be far simpler to transition the existing gas-station infrastructure for accommodating cars using the new battery system. As the battery chemicals are very safe, existing pumps could even be used to dispense these chemicals.

Although sale of electric and hybrid vehicles are growing worldwide, industry and consumers alike are facing the challenge of extending the life and charge of the battery and the infrastructure necessary to charge the vehicle.

At this time, the researchers need more time to complete their research before they can bring the technology to regular use. The researchers are trying to draw interest from investors and working towards publicizing their innovation.

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.

What are Miniature Slide Guides?

Slide guides are industrial mechanical guides to reduce friction in linear motions. They use rolling elements, either hardened steel rollers or balls, moving along two raceways, with a stick-slip arrangement. This provides a smooth linear motion in either direction even when the load is heavy. Usually, slide guides carry their loads on one or more blocks or carriages riding on a rail. Instead of carrying loads, they can also guide other components, making sure they move smoothly and easily along the rail. The rail length depending on the required length of the application is usually made up of several straight sections. For some slide guides, the linear motion can be unlimited in distance, as the rolling elements travel in recirculating paths.

Since the guides are not powered, they cannot provide the drive to move the load. The force to move the load actually comes from a mechanism such as a linear actuator, lead screw, ball screw, or a belt-and-pulley arrangement. A limit switch or some other form of brake outfitted on the linear drive is necessary to stop the motion on a slide guide. Users may also use other stopping mechanisms such as end stoppers or a bumper pad may also be used to halt the motion.

Applications where the space and weight are both limited use miniature slide guides. Although these offer the same functionality and have the same form, miniature slide guides are limited to being only 25 mm in height, and 13 mm or less in width.

People call miniature slide guides with different names such as mini carriage on a profiled guide rail, or mini linear guides. Available in a range of sizes, the performance capabilities of mini slide guides scale with use.

For instance, a load carrying block may be as small as 6 X 12.9 mm, weigh as much as 0.8 gm., and ride on 100 mm rails carrying a load of 2.8 gm. The dynamic load rating for such small guides would be 0.21 kN.

On the other extreme, a block weighing 338 gm., with dimensions of 46 x 79.5 mm, may ride on 100 mm rails with a load of 209 gm. The dynamic load rating for such a large guide would be 12.4 kN. The top speed with which a mini slide guide typically moves is about 1.5 m per second.

Despite their compact size, mini slide guides direct their motion along a linear axis, much as their larger counterparts do. Their main advantage comes from the compact size, allowing them to be used in devices such as robots, medical devices, wafer-fabrication equipment, and hard-disc drives. The mini slide guides also use either balls or rollers as their friction reducing elements.

Mini slide guides use rolling ball elements made of stainless steel or carbon steel. They can support heavy loads and offer a long operational life. An all-stainless-steel construction is best suited for applications such as vacuum or clean rooms.

Mini slide guides that use roller or cylindrical elements offer lines of contact area rather than point contacts as balls do. This allows them to carry heavier loads than slide guides using rolling ball elements can.

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.