Category Archives: Guides

New MEMS Switches Accelerate Testing

If you are using processor ICs from Advanced Digital, testing them may be costly and logistically challenging. This is because testing these ICs requires isolated DC parametric test equipment, including high-speed digital ATE or automatic testing equipment to assuring the quality. New MEMS switch technology from ADI, working at 34 GHz, offers both DC and high-speed digital testing, despite having a small form factor in the form of a 5x4x0.9 mm LGA package. They reduce the test costs and simplify the logistics necessary for testing RF/digital SoCs or systems on chips.

There are many high-speed chips on the market. These include high-density inter-chip communications for advanced processors. Such advanced processors are the norm for 5G modems, computer graphics systems, and other central processing units. Therefore, ATE designers constantly face the increase in demand and complexity for throughput while assuring quality. For instance, the greatest challenge comes from the increasing number of transmitter/receiver channels, and these require both DC parametric and high-speed digital testing. Not only does this increase the testing time, but it also increases the complexity of the load board, while reducing the test throughput. In turn, this drives up operational expenses, while reducing the productivity of modern ATE environments.

One way of solving such ATE challenges requires a switch that not only operates at DC conditions but also at high frequencies. The new MEMS switch ADGM1001 from ADI, while passing true 0 Hz DC signals, can also operate equally effectively at high-speed signals up to 64 Gbps. Therefore, testing with these new switches requires only one insertion for an efficient single test platform. It is possible to configure the test platform for both DC parameter testing and standards for high-speed digital communications.

High-volume manufacturing requiring HSIO or high-speed input-output testing is often a challenge. Testing strategies typically employ a high-speed test architecture as a common approach for validating HSIO interfaces. Such test equipment typically incorporates two test paths in one configuration—one for DC tests, and the other for high-speed tests.

Testers employ a few methods for performing tests at both DC and high speed on HSIOs or digital SoCs. They may use relays, MEMS switches, or different load boards—one for DC testing, and the other for high-speed testing, but this requires two insertions.

Use of relays for DC and high-speed testing can be challenging. This is primarily due to relays being unable to operate beyond 8 GHz. Therefore, users must compromise on test coverage and signal speed. Moreover, relays take up large areas on PCBs on account of their larger size, and this makes the load boards rather large. Another concern with relays is their limited life and reliability. Relays typically only last for about 10 million cycles, thereby limiting the lifetime and system uptime of the load board.

With its superior density and small form factor, the 34 GHz MEMS switch from ADI offers both DC testing and high-speed digital testing capabilities, overcoming the above challenges.

Batteries and Supercapacitors

In the past, only mission-critical devices had them. Now, a wide range of electronic applications demands backup power solutions. These applications include consumer, commercial, and industrial end-products. Of the several options available, the most energy-dense solution is that offered by supercapacitors, acting as energy reservoirs during interruptions of the main supply. Typically, this occurs during an outage of the mains power, or during swapping out batteries.

Although they are versatile, supercapacitors present challenges in design. This is due to their capacity to provide only 2.7 VDC. Potentially, this means adding multiple supercapacitors, along with the necessary cell-balancing circuitry, and voltage converters for step-up and step-down for supplying regulated power to the power rail operating at 5VDC. The solution is a nuanced and complex circuit, which not only takes up excessive board space but is also relatively expensive.

Comparing them with batteries can explain why supercapacitors offer many technical advantages for compact, low-voltage electronic applications. Supercapacitors help in designing simple, elegant solutions for powering a rail operating at 5VDC using only a single capacitor in combination with a buck/boost reversible voltage converter.

Modern electronic devices often need uninterruptible power as a critical element to provide a satisfactory user experience. The absence of a constant power source can not only stop the electronic product from operating, but it can also lead to vital information loss as well. For instance, a personal computer operating from mains power will lose the information contained in its volatile RAM during a power outage. Similarly, important blood glucose readings in the volatile memory of an insulin pump may be lost while replacing its batteries.

It is possible to prevent this from happening by including a backup battery. Not only will the battery store energy, but it can also release it during the failure of the main source of power. Currently, devices typically use lithium-ion batteries, as these are mature technology, offering very good energy density. This allows relatively compact devices to offer considerable backup power for relatively extended periods.

Irrespective of their base chemistries, batteries offer distinctive problematic characteristics under specific circumstances. Not only are they relatively heavy, but they also take relatively long times to recharge, which may be problematic in areas with frequent power outages. Moreover, it is possible to recharge the cells only a limited number of times, thereby increasing maintenance costs. In addition, batteries often include chemicals that can introduce environmental and safety hazards.

The supercapacitor, or ultracapacitor, offers an alternative solution. Technically, the supercapacitor is a capacitor with an electric double layer. Manufacturers construct supercapacitors using electrochemically stable, symmetric positive and negative carbon electrodes. They separate the electrodes by an ion-permeable separator that is insulating and use a container that they fill with an organic salt/solvent electrolyte.

Supercapacitor manufacturers design the electrolyte to maximize electrode wetting and iconic conductivity. The combination of the minuscule charge separation and high surface area of activated carbon electrodes results in the very high capacitance of the supercapacitor, as compared to the capacitance of regular capacitors.

The reliance on electrostatic mechanisms to store energy makes the electrical performance of supercapacitors more predictable than those of batteries.

Electronically Commuted Motors — Higher Efficiency

Restaurant owners have long been facing operational challenges. These include high energy costs, limited kitchen space, and equipment downtime. For addressing these challenges and improving restaurant productivity, the owners have turned to commercial kitchen equipment. Most of such kitchen equipment has an electric motor at heart, whose performance dramatically impacts how the equipment operates and how it mitigates the above challenges.

It is imperative that owners increase their productivity while reducing their costs, considering their profit margin usually falls between three and five percent. This requires a clear understanding of the connection between the motor and the equipment. Doing so not only reduces the operating costs but also ensures a smoother running operation.

Energy costs happen to be a major concern in the restaurant industry. Commercial kitchen equipment is uncommonly hard on the electricity bill, being typically robust and energy-intensive. According to the US Energy Information Administration, consumption in restaurants is typically three times more per square foot than any other comparative commercial enterprise. This is because restaurants use specialized equipment that has a high power demand, and they operate for extensive hours, thereby consuming huge amounts of energy.

Therefore, purchasing and using high-efficiency, higher energy star-rated restaurant equipment is one of the easiest ways to improve the bottom line. However, as a motor is at the heart of each piece of equipment, it offers a greater choice. In fact, restaurant operators can improve on this further by taking a proactive approach and selecting equipment that has an electronically commuted motor or ECM. They can even consider retrofitting existing equipment with ECMs for a more favorable option.

The reason for the above decision is that an ECM operates more efficiently as compared to what a traditional induction motor does when running restaurant equipment such as ovens, walk-in coolers, mixers, and fryers. Depending on the use cycle, equipment with ECM technology can save more than 30% in annual energy costs. This improves the bottom-line savings and improves the profitability of a restaurant.

A microprocessor and electronic control help to run an ECM. Compared to regular induction motors, this arrangement offers higher electrical efficiency. It also offers the possibility of programming the precise speed of the motor. Moreover, ECMs can maintain high efficiency across a wide range of operational speeds.

Apart from the higher efficiency, ECMs are precise and offer variable speeds, which in fans means an unlimited selection of airflow. A properly maintained airflow during changes in the static air pressure brings important benefits to the restaurant, especially for its hood exhausts and walk-in coolers. The higher efficiency of ECMs leads to reduced heat in the refrigerated space, thereby reducing the equipment runtime.

Forward-thinking original equipment manufacturers are re-engineering their designs and products to include ECMs for delivering smaller and more versatile equipment. Compact motors such as ECMs, are gaining wider recognition and appreciation as they improve the power density of their equipment. Compared to equipment with traditional induction motors, those using ECMs offer the same output, but with a much smaller footprint and lower weight.

Industrial Automation with Single-Pair Ethernet

Efficiency is the fundamental concern for the successful implementation of any factory automation solution. For this, it is necessary to implement control and power components that consume the least possible amount of energy over their lifetime. However, for the actual realization of those savings, it is necessary for proper installation of the system.

This is where the advantages of the SPE or Single Pair Ethernet technology really come across. The technology transfers power and data over the same thin-wire cable. Not only does this save installation costs up-front, but it takes much less to maintain and upgrade the system over time. Phoenix Contact offers their ONEPAIR series for standardized SPE solutions. The ONEPAIR series has two main types of connectors, and they each serve a specific application.

In numerous industries and fields, the IP20 connectors and patch cables enable effective data transmission. This includes building and factory automation, where it is common to achieve a transmission rate of 1 Gbps for a distance of 1000 meters.

The other is the M8 device connectors, rated at IP67. They can transmit power and data safely and quickly from the OT to the IT. This is a new standard in compact connections, which can withstand harsh environments.

SPE or single-power Ethernet is high-performance, parallel transmission of power and data via Ethernet over a single pair of wires. The technology typically carries data and power through PoDL or Power over Data Line starting from the sensor and carrying through right up to the cloud. For barrier-free networking of a wide range of connectors, cables, and components, it is necessary to deploy connectors with standardized pin patterns. For this, Phoenix Contact offers standard connectors, ranging from IP20 to IP6x.

Apart from being ideally suited for a wide range of applications, the SPE is the basis for all Ethernet-based communication. Not only does it enable smart device communication, but it also opens up newer fields of application. SPE has great transmission properties, can span long distances, and optimally supports future-proof network communications. With a trend for miniaturized, resource-conserving devices, SPE offers space-saving cables and electronics.

SPE brings many benefits to its users. It can provide transmission speeds of over 10 Gbps over a single pair of wires. This helps to reduce data cabling while avoiding media breakdowns and device failures, from the field to the cloud. The user has the freedom to establish networking with a consistent structure base of Ethernet, eliminating the need for gateways. With SPE, the cabling is easier and saves time, as the user needs to guide and connect only two wires. They can use the 10Base-TIL standard Ethernet cabling for ranges up to 1000 meters.

The IEEE 802.3 defines the SPE standards. Presently, there are five standards for different transmission speeds and distances. Further standards are under discussion. The IP20 compact male connector series from Phoenix Contact are in accordance with IEC 63171-2 and are ideally suited for building and control cabinet cabling. The M8 or IP67 contacts from Phoenix Contact are in accordance with IEC 63171-5, providing robust and industrial-grade connections.

What is I3C Interface Communication

I2C is a popular serial communication protocol, with I3C being an improved version. Embedded systems use this new protocol for achieving significantly higher data throughput and features that are more advanced than what I2C offers. Designers and engineers can use I3C for improving the functioning and performance of their designs while adding more features such as in-band interrupts, hot-join, and high data rate modes. With I3C being backward compatible, it can communicate with legacy targets using the present I2C protocol.

There are some major differences between I3C and I2C. While I2C works on bus speeds of 100 kHz, 400 kHz, or 1 MHz, I3C operates with bus speeds up to 12.5 MHz. The increase is due to I3C using push-pull outputs, which switch between push-pull drivers and open-drain outputs depending on the state of the bus. I3C uses open-drain driving during arbitration or initial addressing where multiple targets are controlling the line at the same time. I3C uses the push-pull driver for unidirectional communication, and no other device is expected to communicate simultaneously.

The voltage range of operation of I2C is between 3.3 and 5 VDC, and I3C operates with supply voltages of 1.2, 1.8, and 3.3 VDC, with the possibility of other voltages in between. Unlike 12C, I3C does not require external pull-up resistors, as the main controller on the bus provides these.

I2C uses static 7-bit and 10-bit addressing of target devices. On the other hand, I3C makes use of dynamic 7-bit addressing, where the active controller designates each target with an unambiguous address to prevent collisions with addressing. In contrast, I2C requires the designer to keep track of the current addresses to prevent assigning the same address to two or more devices. I3C assigns addresses dynamically during bus initialization.

I2C has no mechanism for a target to tell the controller that data is ready unless it uses an extra IO line. However, devices in I3C can signal an interrupt by using the serial data and serial clock lines, thereby making the protocol truly two-wire. I3C also uses this in-band signaling for implementing hot-join functionality. This allows new devices to join once the initial address assignment is over.

I2C allows multi-controller buses. Here, although multiple devices can operate as controllers, only one of them can actively communicate at a time. On the other hand, I3C can have only one active controller, while other capable devices can request to become active controllers on the bus. This device can then become the secondary controller. If the secondary controller is no longer acting as an active controller, it starts functioning as an I3C target.

I3C is backward compatible with I2C. However, for successful communication, the targets in the I2C protocol must have a 7-bit address, and must not use clock stretching. The new protocol suggests the I2C targets contain 50ns filters on their inputs. By meeting these requirements, I2C targets become compatible with the I3C bus. On the other hand, a few I3C devices may also operate as I2C targets, until they have been assigned a dynamic address. When working in the I2C mode, the I3C devices have static communication addresses.

Micro 3D Printing for Miniaturization

Engineers have been using additive manufacturing for prototyping for about 30 years now and are also using it for production. However, the biggest value addition from additive manufacturing comes from producing parts that other traditional manufacturing methods find difficult.

Fabricators use additive manufacturing as a valuable and important solution for producing parts such as those including complex design features like internal geometries and cavities that are impossible to achieve by regular machining. Additive manufacturing is helpful in producing structural elements that are too cumbersome or difficult to generate effectively by conventional means.

At present, engineers use 3D printers for printing large parts quickly. These parts may have resolutions around 50 µm and tolerances around 100 µm. However, sometimes, they also need to produce parts with sub-micron resolutions that are smaller than 5 um. Therefore, they needed a system for printing micro-sized parts at a reasonably high print speed.

Smaller parts require a more precise production process. For instance, cell phones and tablets, microfluidic devices for medical pumps, cardiovascular stents, MEMS, industrial sensors, and edge technology components require connectors with high resolution and accuracy. Most standard additive manufacturing machines cannot provide the resolution necessary for micro-sized parts.

BMF or Boston Micro Fabrication designs and manufactures the PµSL or Projection Micro Stereolithography technology-based printers. Using PµSL printers, it is possible to create 3D printed parts with 2 µm resolution at ±10 um scales. These 3D printers incorporate the benefits of both the SLA or stereolithography technologies and the DLP or digital light processing technologies.

Using a flash of ultraviolet light at microscale resolutions, these PµSL printers cause a rapid photopolymerization of an entire layer of resin. This takes place at ultra-high precision, accuracy, and resolution, not possible to achieve with other technologies.

For faster processing, the PµSL technology supports continuous exposure. Other design elements allow additional benefits to the user. For instance, in printers using the standard SLA technology, the bottom-up build method requires a support structure to hold the part to the base, while also supporting the overhanging structures. Conventional SLA systems can typically achieve resolutions of 50 µm, an overall tolerance of ±100 µm, and a minimum feature size of 150 µm. Similarly, standard DLP systems using a similar bottom-up build structure offer 25-50 µm resolution, an overall tolerance of ±75 µm, and a minimum feature size of 50-100 µm.

On the other hand, the PµSL uses a top-down build, thereby minimizing the need for a support structure. It also provides a way to reduce damage while removing bubbles with a transparent membrane. Comparatively, PµSL systems offer resolution down to 2 µm, dimensional tolerances as high as ±10 µm, and minimum feature sizes of 10 µm.

BMF provides this type of quality by properly employing every system component. This includes the resolution of the optics, controlling the exposure and resulting curing, the precision of mechanical components, and the interaction between parts and required support structures. It also depends on the ability to control tolerances across the build and the overall size of the part. Moreover, working with such diverse micro parts requires choosing the right material characteristics.

Using Ferrites in Wire Assemblies

The phenomenon of magnetism is prevalent all over the world, along with related concepts like the magnetic field, electromagnetism, and electromotive force. Although these are complex subjects at a higher level, they are easy to understand. However, these are principles on which electric motors operate, the earth’s magnetosphere shields life, and refrigerator doors remain closed.

The wonderful properties of magnetism also help products and applications like cable assemblies. There are well-known magnets like those made of neodymium, and these are permanent magnets with inherent magnetic properties. They comprise elements of Neodymium, Boron, and Iron. Neodymium magnets are among the most powerful permanent magnet types available. In comparison, there are non-permanent magnets also. Typically known as electromagnets, they derive their properties from the passage of an electrical current.

Other types of permanent magnets are also available. The most popular of these is the ferrite magnets, and industries use them for a lesser-known reason. Used in various forms like chokes, cores, and beads, these inexpensive devices greatly help filter electrical noise and get products to comply with EMI/EMC regulations. Countless design applications use them in different form factors and are available from numerous manufacturers. Ferrite magnets comprise a mixture of iron oxide and ceramic magnets. In doughnut-like shapes, they keep control over signal integrity within bundles of wire. For instance, a data cable carrying high-frequency data transmission,  when routed through the magnetic field of a ferrite, can eliminate unwanted electrical noise, as the ferrite acts as a passive EMI filter.

For a ferrite to be effective, the cable must pass through the center of the ferrite and its magnetic field. Looping and routing the wire multiple times through the ferrite helps incrementally improve the signal integrity. While a majority of cables have their wires passing through the ferrites only once, some designs require them to make as many as three loops to meet design objectives. Typically, there are two types of ferrites available that are suitable for cable assemblies—snap-on ferrites and doughnut ferrites.

Snap-on ferrites are the easiest to assemble. These are passive suppression devices with two halves. A plastic clamshell case holds the two halves as it snaps close around the wire. Available in a wide variety of sizes for different cable diameters and performance types, these are excellent devices that can mix and match various types of ferrite to help pass an aggressive test requirement. However, snap-on ferrites can be expensive and require accurate sizing to match the wire’s outer diameter to create an interference fit. As their design is like a clamshell, it is easy to remove snap-on ferrites.

Doughnut ferrites are simpler, being in the shape of a ring or a doughnut. The cable must pass through the center of the continuous circle of the ferrite before the wires terminate into a connector. The doughnut ferrite is therefore a permanent fixture, unlike the snap-on ferrite that the user can remove at any time. Overmolding the ferrite helps to fix its position on the cable while protecting the brittle ferrite magnet from damage.

What is Soldering?

Although soldering electronic components in place is a complex activity, most people involved with the soldering process do not realize it. Complicated chemical and thermal processes occur within a very small space when soldering. To make a good solder joint, it is necessary to follow a few basic rules.

Apart from just making good electrical contacts, solder joints should also be mechanically strong and must not oxidize. Additionally, there should not be chemical residues in the joint. Usually, chemical residues come from flux, which can corrode plastic and metallic surfaces both.

Manufacturers offer solder in three categories—consumer, industrial, and high-end. The automotive and health industry makes use of the third category. Consumer and industrial grades are more common for manual, automated, and other construction purposes.

For several years, the standard was the leaded solder. With a relatively low melting point of around 183 °C, leaded solder has good flow and wetting characteristics. For proper melting and formation of a good solder joint, the recommended temperature at the tip of a soldering iron is 120 °C above the alloy’s melting temperature. This corresponds to a tip temperature of about 300 °C.

Manufacturers provide flux inside the hollow of the solder wire. The flux helps to dissolve oxides of the metals at the solder joint. General purpose leaded solder is typically an alloy of tin and lead in the ratio 63:37. Typically, the tin in the alloy amalgamates with the metal (typically copper), producing an alloy of the two metals, as an intermetallic diffusion zone. This helps to form a good solder joint, well-formed, mechanically strong, and durable.

However, an ideal solder joint does not happen in all cases. Sometimes, the solder forms a cold solder joint. Reasons for the formation of a cold solder joint are the presence of highly oxidized metals and dirt, inadequate heating, or fast cooling after the melting process. Inadequate wetting is common in cold solder joints, leading to easy detachment of components.

It is easy to recognize a cold solder joint with leaded solder. The joint has a dull matte surface against a shiny, glossy surface of a good solder joint. With lead-free solder, this is no longer the case. Newer alloys of lead-free solders usually form a matte surface. However, this depends on the specific composition, and it remains matte whether the solder is establishing a good or a cold joint.

New lead-free solders are RoHS compliant, meaning they do not contain certain hazardous substances, as specified by the EU Directive and the Restriction of Hazardous Substances.

The lead content in lead-free solder cannot cross a 0.1% limit. The intention is to prevent the operators from inhaling toxic vapors. Earlier, the use of suitable extraction systems prevented the risk of such inhalation, provided they were in actual use.

The absence of lead in lead-free solders has resulted in an increase in their melting point. The presence of about 95% tin raises the melting point of the alloy from ~217 °C to ~227 °C. This also changes the flow characteristics. Higher temperatures mean the actual soldering time must be small to prevent damage to the components.

Advanced Solutions for Electric Vehicles

Although EVs or electric vehicles have existed in some form or the other for many hundred years now, it is only in the past few decades that technology has advanced and companies have found success. With concern over the effects of air pollution, climate change, and an ever-diminishing supply of fossil fuel, more and more people are considering changing over to EVs.

Consumer demand constitutes the basis of the growing popularity of EVs. The role of governments also helps by tightening their regulations and mandates in reducing carbon emissions with an effort towards reducing global warming.

The rapidly increasing rate of growth of EVs is presenting a huge opportunity not only for EV manufacturers alone, but also for OEMs, and suppliers of aftermarket parts. Although there has been a significant advancement in EV technologies and solutions over the past few decades, there are still a few challenges that must be overcome, and which can quickly become hindrances. Manufacturers must develop new and innovative ways of addressing these challenges if they want to continue on the path to success.

At present, there are three important considerations that most consumers stipulate manufacturers must overcome—range anxiety, performance, and cost.

Even among modern EVs, many could not go very far without their batteries needing a recharge. For most people, this range was too small to seriously consider a changeover to fully electric vehicles. Although battery and motor technology have advanced significantly, range anxiety is still a factor.

Even two decades ago, EVs were struggling to match the performance and power of fossil-fuel-powered vehicles.

As with any new technology, EVs were initially expensive. Typically, modern EVs were far beyond the reach of most people, or what people were willing to pay for them.

Although car manufacturers are actively addressing the above challenges, an EV that is affordable enough for most consumers and does not compromise on performance, and one that requires only a single charge a month, is still only a mirage. Right now, manufacturers are busy balancing tradeoffs between range, performance, and cost. For instance, improving the performance affects range and cost, while cutting costs can severely compromise range and performance.

Fortunately, manufacturers are finding enhancing efficiency to be the key to the solution. For instance, the primary bottleneck to improving range is the capacity of the battery. Although the obvious solution is to use a bigger battery, that complicates matters further. Not only do bigger batteries cost more, but they also weigh more. Therefore, a bigger battery while increasing the vehicle’s cost can also decrease its performance.

Therefore, manufacturers are looking for ways to use the existing battery more efficiently. They are reducing the energy losses occurring naturally in the power-conversion system of the vehicle. This is mainly as lost energy in the form of heat in the EV’s motor, powertrain, and the power-electronics systems in the vehicle.

Weight is another factor affecting performance—a lightweight vehicle has superior performance. Therefore, manufacturers are trying for higher power density, where they add more power to the vehicle without increasing its weight. With lighter batteries and power-conversion systems, the vehicle can achieve better performance and speed.

A Digital Analog Hybrid Standard

In the industrial world, instruments typically communicate with one another over two wires by conveying a 4-20 mA analog instrument signal over them. To improve communication, engineers introduced a technological advance, which they called HART or Highway Addressable Remote Transmitter. HART is a hybrid communication standard that allows instruments to digitally communicate over the same 4-20 mA DC signal wires.

HART offers two channels of communication for instruments. One variable channel for communicating using the analog value of a 4-20 mA DC signal. The other variable channel offers digital communication using pulses of current representing binary bit values of 0 and 1, utilizing several variables. With the digital current pulses superimposing upon the analog DC current signals, the same two wires can carry both analog and digital data simultaneously.

A typical standard loop-powered, two-wire process transmitter has a DC power supply and a 250-ohm resistor for creating the 1 to 5 V signal from the 4-20 mA current signal that any voltage-sensing recorder, controller, or indicator can read easily.

In such circuits, the primary function of the transmitter is to regulate the current to a value representing the process variable it is measuring. The process variable may represent flow, temperature, pressure, etc. that the circuit measures using a current range of 4-20 mA. The DC voltage source provides the necessary power for operating the transmitter. In industrial instrumentation, such loop-powered instruments are common, as they allow conveying of both power and data on the same pair of wires.

With process transmitters now involving microprocessors, the instrument technicians can configure parameters digitally within the transmitter. These include damping values, range values, and more. They can query the transmitter for self-diagnostic alarms. However, to make full use of the digital functionality, it is necessary for the process transmitter to be able to communicate digital data to and fro over the same two wires that convey the 4-20 mA analog signal.

Another way of accessing the digital data within the transmitter would be to connect a communicator to a data port located on the transmitter. However, this would be inconvenient considering the location of these transmitters, mainly in inaccessible places in the industry, making it difficult to carry a personal computer or other communication devices to the transmitter.

The communication protocol, HART, solved the issue by adding digital data in the form of AC signals using audio-frequency tones, along the same two wires that carried the 4-20 mA DC current signal. A smart transmitter, with a modem built into it, translates these digital binary bits into AC signals, and vice-versa.

This allowed instrument technicians to communicate with the new microprocessor-equipped transmitters. They can do this simply by connecting a HART modem at any point on the two-wire cable, even at the far end, where it terminates at the hardware of the control system.

The ability to transmit and receive digital data over the same wire pair carrying the analog signal and DC power opens an entirely new range of possibilities. Now, technicians can send and receive status reports, self-diagnostic information, multiple process variables, alarms, and more in addition to the original signal representing the primary process variable.