Industrial Wireless Networks

Industrial wireless networks (IWNs) are a key enabler of many aspects of advanced manufacturing. IWNs promise lower installation costs compared with wired alternatives, increased operational flexibility, improved factory visibility, and enhanced mobility. Wireless networks are not dissimilar to wired networks with the key exception being the transmission medium. Wired networks typically operate over copper wires, coaxial cable, or fiber optic cable depending on the network type. Wireless networks operate without wires or cables using the electromagnetic propagation. As such, wireless networks operate within a shared medium that is publicly accessible. A listing of wireless technologies is listed below:

Home and Office
This includes standards-based communications system typically found in the office environment but may be useful for the factory. Includes IEEE 802.11 variants and Wi-Fi compliant devices. Bluetooth also falls into this category.

Instrumentation
Includes systems specifically designed for factory operation. IEEE 802.15.4 standards such as International Society of Automation (ISA) 100.11a, WirelessHART (IEC 62591:2016), IEC 62601, and ZigBee fall into this category. High-performance standards built on IEEE 802.11 include the Wireless Networks for Industrial Automation - Factory Automation (WIA-FA) IEC 62948. Many exceptional proprietary options exist as well.

Wide Area Sensing
Some applications require the ability to transmit over long distances with minimal power to conserve battery life for sensing and control over wide geographical distances. Examples include LoRaWAN and Sigfox as well as modes of 4G and 5G cellular radio standards.

Other commercial
This category includes systems such as satellite, cellular, directional microwave data links, optical (visible light), and land-mobile radio. This category includes technologies supporting video and voice communication.

Analynk A75x RF Industrial Wireless DIN System

Analynk A75x

The Anaynk A75x series offers simplicity and reliability in a point to point, multipoint or wireless mesh system. One A753 transmitter can communicate with multiple A750 receivers for redundancy. A repeater can be added simply by placing in between a transmitter and receiver, no programming is required. Three radio options are available: long range 900MHz 1W, 900MHz 50mW and 2.4GHz 63mW. In addition to transmission of the industry standard 4-20mA, our transmitters can directly process thermocouples, RTD and switch states. Up to 32 inputs may be transmitted with one transmitter when the A753 is paired with our A16000 expansion module.

MODEL NUMBERS:

• A750 Receiver
• A750-Mod (RS232/485)
• A753 Transmitter
• A759 Repeater
• A753-PL Transmitter (pulse)
• A750-PL Reciever (pulse)
• A753-LP Transmitter (900MHz 50mW)
• A750-LP Receiver (900MHz 50mW)

FEATURES:

• 35mm DIN rail mount
• Standard 1W long range output, optional 50mW & 63mW
• Removable 2.0dBi dipole antenna
• DIP switch selectable channels
• Signal Strength indicator
• Repeaters available
• No software required
• Factory configured for your application

APPLICATIONS:

• Remote 4-20mA installation
• Redundant 4-20mA outputs
• Temperature monitoring
• Tank level monitoring
• Remote switch monitor
• Pulse transmission
• Remote alarms
• Rotating devices (e.g. kilns)
• Temporary 4-20mA

For more information, contact Analynk Wireless by visiting https://analynk.com or by calling (614) 755-5091.

The Move Toward Industrial Wireless Control

Demands for safety, reliability, efficiency, and quality put manufacturing plants under tremendous pressure. Unexpected shutdowns and outages have devastating effects on plant performance. Lost production, increased energy costs, unplanned maintenance costs, and augmented safety concerns are outcomes of equipment failure. Tomorrow's technologies must mitigate these process control realities.

Wireless technology is a serious contributor in the effort to improve plant efficiency, lower risk, and increase productivity. Wireless transmitters are available for monitoring virtual all process variables such as pressure, temperature, level, flow, and density. In harsh environments these devices provide critical performance data transmission around the clock.

Wireless instrumentation provides a compelling argument when you consider installation cost savings and convenience.  The cost savings associated with the elimination of wires and cables is estimated to be as high as 70% when compared to the cost using cables for the same application. Furthermore, wireless instruments keep personnel out of hazardous areas, providing additional safety and compliance benefits.

All industries face cost cutting realities as they strive for continuous process improvement.  The need to build a better mousetrap is always present. Before widespread adoption of wireless occurs, concerns about reliability, acclimation, and integration must be overcome. But, as deployment costs are reduced, maintenance costs are reduced, employee safety is improved, and environmental compliance is advanced, wireless instrumentation adoption with continue to accelerate in modern process control installations.

Prefabricated Wireless Communications Solution

Wireless transmission of process measurement and control signals has not been new technology for quite some time. In many cases, wireless connection is the installation method of choice over cabled. The benefits in speed of implementation and cost are substantial. That said, as the technology continues to permeate industrial installations of every size, there still remain facilities where it has not made any inroads yet. 

When technology is new to the industrial market, especially if it challenges the current way things are done, early adopters with larger scale, higher dollar operations are needed to put the technology into practical use and generate manufacturing volume for the technology producers. If deployment of the technology proves beneficial, the market grows on the consumer and producer sides. With greater efficiency and scale, coupled with growth in the knowledge base throughout the market with increased penetration, costs tend to decrease, while the range of feasible applications and projects grows.

Wireless communication for industrial applications is well beyond the point of early technology adoption. Protocols are in place, products for the transmitting and receiving of wireless process signals are mature. As a stakeholder at any level of a processing operation, you should confidently consider wireless connections between measurement and control or recording devices as part of any new installation or upgrading of existing facilities.

Analynk's wireless demo kit includes a model A750 receiver and A753 transmitter both housed in NEMA 4 enclosures. The kit operates at 900 MHz with full 1W power. Locate the transmitter and receiver at points where you wish to establish a wireless connection. You can provide your own input signal, or use the provided simulator to show that a wireless connection can be established and function in a manner that will give you confidence to move forward with implementation. The kit is useful for testing out possible new locations for distance and signal strength. You will use it as wireless communications expand through your facility. Test the location first, then order the needed wireless equipment. It's a solid and low risk solution.

An additional use of the prefabricated transmitter and receiver stations is as a temporary portable means of establishing a connection between measurement and control points. The units can even be solar or battery powered, if no power source is available.

Analynk is a manufacturer of both wireless and wired devices for process measurement and control. The company's offering includes a wide array of standard products, as well as integration and customization to meet specific project requirements. Contact the specialists at Analynk to discuss your industrial wireless application requirements.

Wireless Process Connections - DIY May Not Be Your Best Option

Analynk can design and fabricate complete systems for
establishing wireless process connections.

Implementing in-house projects takes time, something you may not have enough of on a good day. Establishing wireless connections between remote sensors and control or monitoring equipment can be accomplished with a minimum investment of scarce in-house human resources using Analynk's design and build services. With an extensive range of standard products, accessories and options, Analynk will assemble ready-to-run panels for the transmitting and receiving ends of your wireless link. This saves a substantial amount in resources that would otherwise be devoted to design, layout, assembly and operational testing of each panel needed. Smart outsourcing.

The Analynk application team can design and fabricate a complete package solution for your process measurement or wireless connectivity requirement. Share your ideas and challenges with the wireless and process measurement experts, leveraging your own knowledge and experience for a successful project outcome.

Use Signal Repeaters to Overcome Industrial Wireless Transmission Barriers

A repeater can be used to overcome barriers to signal
transmission, such as distance and structures.

Many process measurement and control wireless connections are accomplished using networks, with routers and access points. Other connections are established across longer distances, conceivably outdoors. In many of those cases, there are barriers or obstructions that will attenuate the wireless signal sufficiently to prevent reliable data transfer. Hills, wooded areas, walls, tanks and other structures and natural features can present real challenges to wireless signal transmission. Another transmission challenge is the distance between transmission and receiving stations.

One, though not the only, solution to overcoming the challenge that can arise due to extended distance or substantial obstacles between the transmitter and receiver is the placement of a repeater. Analynk provides a repeater that can be strategically located between transmitter and receiver to extend the overall transmission distance, or route the signal around obstacles that may otherwise degrade the transmission. The data sheet included below describes how easy it is to apply and provides all the technical details.

Wireless connectivity is an incredibly flexible option for delivery of process data from measurement point to control point. Contact Analynk with your wireless communication challenges and get solid practical solutions.

Analynk Model A759 Wireless Repeater from Analynk Wireless, LLC

Updated and Expanded Wireless Equipment Enclosure Options

Analynk customizes wireless equipment enclosures to
provided customers ready to run solutions.

Analynk offers customizing and fabrication of wireless equipment enclosures to meet every customer requirement. Combining their industrial wireless transmitters, receivers, repeaters, antennas, and other components into a fully assembled package, Analynk can save customers time and cost with a complete and ready to run solution for establishing wireless process instrument connections across almost any distance.

The company recently updated the documented offering for enclosure options. If you have the old document, you should replace it with the newest version.

Share your industrial wireless connection requirements and challenges with the experts at Analynk. Combining your own knowledge and experience with their application expertise will deliver an effective solution.

It's Been A Good Year for Us.

Industrial wireless transmitter and receiver

Things have been busy at Analynk this year. As the year closes, we would like to extend our thanks to all those who supported us with their business and their efforts on our behalf. Working together, the Analynk organization accomplished some notable goals.

• Introduced several new hazardous area enclosures for wireless access point equipment.
• NEMA 4X designation on all explosion proof antennas
• Expanded line of specialty enclosures for wireless transceiver equipment
• New larger hazardous area rated RF enclosure for wireless equipment
• Custom designed OEM products or systems
• Continued expansion of 3D product drawing library
• Updated and expanded distributor network with seasoned professionals

Next year is already shaping up to be even better, with more innovative and creative products for establishing wireless process control connections across the room, across the property, and around the globe.

Integrating Products Into a Complete Solution

Explosion proof temperature transmitter, one of many
Telmar process measurement products.

Analynk Wireless manufactures equipment and crafts solutions for establishing wireless connections between process measurement and control locations, across the room, across the property, around the globe. As part of the company's product matrix, their Telmar branded products provide measurement points for complete application solutions. A review of the Telmar products.

• Pressure to current transmitters
• Current to pressure transmitters
• Pressure to voltage or current
• Current or voltage to pressure
• Voltage to current
• Current to voltage
• RTD
• Thermocouple
• Slidewire
• Tachometer
• Power supplies
• LCD digital meters
• LED Indicators
• Signal alarms

The Analynk application team can design and fabricate a complete package solution for your process measurement or wireless connectivity requirement. Share your ideas and challenges with the wireless and process measurement experts, leveraging your own knowledge and experience for an effective project outcome.

Tachometer Transmitter for Industrial Process Measurement and Control

Tachometer transmitters deliver rotational speed signals

Analynk Wireless, in addition to producing their line of products for establishing wireless connections among industrial process measurement and control devices, manufactures an extensive array of wired products. The wired products are useful in establishing similar connections between sensors and the devices or instruments that will utilize their output signals. The transmitters are available with a wide array of input and output combinations, as well as several enclosure options. Enclosures can be customized to meet specific installation challenges.

The tachometer transmitter will convert the pulse signal from a tachometer into a linear signal representing rotational speed. There are many applications where a frequency output from a tachometer or other sensor needs conversion to a 4-20 mA or other common signal for use by a monitoring instrument. Analynk provides transmitters to easily convert almost any sensor signal to a linear voltage or current output. A data sheet is included below that provides more detail about one of the many transmitters available from Analynk.

Share your connectivity challenges with the process signal transmission experts at Analynk. Effective solutions come through consultation and cooperation.

Tachometer transmitter for industrial process measurement and control from Analynk Wireless, LLC

Solar Powered Wireless Communications for Industrial Process Measurement and Control

Analynk Model A650 Solar Power Supply

Wireless connections of process measurement and control equipment sometimes are accomplished in remote locations without readily available electric power. Analynk, as part of its full line of industrial wireless connectivity products, provides their model A650 Solar Power Supply for locations that require a small amount of DC power to operate instrumentation and an Analynk transmitter.

The power supply unit comes complete with solar panel, battery, charge controller, and NEMA 4 enclosure. Options are available to accommodate specific installation requirements. Custom units can be designed for larger power requirements and other special applications.

The data sheet below provides more detail. Share your wireless process measurement and control connectivity challenges with Analynk for effective solutions.

Solar power supply for industrial wireless transmitters from Analynk Wireless, LLC

RTD or Thermocouple for Your Temperature Measurement Application?

Wireless transmission of temperature signals can be
easily accomplished with Analynk transmitters and receivers

Proper temperature sensor selection is key to getting useful and accurate data for maintaining control of a process. There are two main types of temperature sensors employed for industrial applications, thermocouple and resistance temperature detector (RTD). Each has its own set of features that might make it an advantageous choice for a particular application.

Thermocouples consist of a junction formed with dissimilar conductors. The contact point of the conductors generates a small voltage that is related to the temperature of the junction. There are a number of metals used for the conductors, with different combinations used to produce an array of temperature ranges and accuracy. A defining characteristic of thermocouples is the need to use extension wire of the same type as the junction wires, in order to assure proper function and accuracy.

Here are some generalized thermocouple characteristics.

• Various conductor combinations can provide a wide range of operable temperatures (-200°C to +2300°C).
• Sensor accuracy can deteriorate over time.
• Sensors are comparatively less expensive than RTD.
• Stability of sensor output is not as good as RTD.
• Sensor response is fast due to low mass.
• Assemblies are generally rugged and not prone to damage from vibration and moderate mechanical shock.
• Sensor tip is the measuring point.
• Reference junction is required for correct measurement.
• No external power is required.
• Matching extension wire is needed.
• Sensor design allows for small diameter assemblies.

RTD sensors are comprised of very fine wire from a range of specialty types, coiled within a protective probe. Temperature measurement is accomplished by measuring the resistance in the coil. The resistance will correspond to a known temperature. Some generalized RTD attributes:

• Sensor provides good measurement accuracy, superior to thermocouple.
• Operating temperature range (-200° to +850°C) is less than that of thermocouple.
• Sensor exhibits long term stability.
• Response to process change can be slow.
• Excitation current source is required for operation.
• Copper extension wire can be used to connect sensor to instruments.
• Sensors can exhibit a degree of self-heating error.
• Resistance coil makes assemblies less rugged than thermocouples.
• Cost is comparatively higher

Sensors are often part of a transmitter assembly that provides an output signal suitable for connection to controllers or monitoring instrumentation. Challenges of distance can be easily overcome using Analynk's wireless process control connection products. Whether the distance is meters or miles, Analynk has a solution that is effective and simple to apply.

Each industrial process control application will present its own set of challenges regarding vibration, temperature range, required response time, accuracy, and more. Share your process temperature measurement requirements and challenges with a process control instrumentation specialist, combining your process knowledge with their product application expertise to develop the most effective solution.

Specialty Valve for Transmitter Isolation

Transmitter Isolation Valve
Courtesy PBM Valve Solutions

Fluid process control applications frequently employ tanks and vessels as part of the processing chain or for storage and holding. Level transmitters can be installed on the tank to provide indication of liquid level. While there are numerous combinations of fittings and valves that could be used to mount and connect the transmitter to the tank, one manufacturer, PBM Valve Solutions, has designed a specialized valve intended to mate a transmitter to a tank fitting with great advantage.

The specialized transmitter isolation valve minimizes dead space to prevent media residue buildup. It can be configured to accommodate CIP and drainage without process interruption. Calibration ports and industry standard mountings allow for broad application throughout the fluid process control industries.

Establishing a connection between the transmitter and its associated monitoring or control equipment is a specialty of Analynk Wireless. Analynk provides end to end solutions for delivering transmitter signals using wireless communications that can span across the room or around the globe. Reach out to Analynk for effective and easy to implement wireless solutions.

Analynk's Telmar Brand of Process Control Products

Telmar enclosed 2-wire transmitter

Analynk Wireless, in addition to wireless process signal transmitters, receivers, and repeaters, manufactures a broad line of industrial process control products under the Telmar brand.

• 2-Wire Transmitters with AC, DC, mA, slidewire, RTD, or tachometer inputs. General purpose enclosure is standard, with options for others to meet any rated environment.
• 4-Wire Transmitters with dozens of combinations of input and output signals. Alarm outputs available as option.
•  Signal Alarms that accommodate inputs from thermocouple, DC current, DC voltage, RTD, AC voltage, AC current, tachometer, slidewire, or strain gauge.
• Pneumatic Transmitters for pressure to current, current to pressure, pressure to voltage, and voltage to pressure applications.
• Tachometer Transmitters
• Explosion Proof Transmitters with or without local indicator for thermocouple or RTD input.



RTD transmitter with explosion proof enclosure and display

• Indicators and Meters with general purpose or explosion proof enclosures in loop powered or external powered versions.
• Sensor Assemblies for general, corrosive, or explosion proof applications. Thermocouple or RTD.

The Telmar brand provides complementary products for wired process control applications, or can be supplemented by Analynk's wireless products to provide wireless connectivity between point of measurement and point of control.

Reach out to Analynk with your process control challenges, combining your process knowledge with their product expertise to develop effective solutions.

Magnetic Level Indicators For Tank Level Measurement

Magnetic Level Indicator
Courtesy Orion

The magnetic level indicator (MLI), also called a magnetically coupled liquid level indicator or a magnetic level gauge, is in wide-spread use throughout process industries around the world. Originally designed as an alternative to sight glass gauges, MLIs are now commonly specified in new construction and plant expansions.

Principle of Operation

Magnetic level indicators use magnetic force couple the position of a float to a scale that indicates actual liquid level in a tank. The float movement and scale can be used to activate a switch or provide continuous level data via a transmitter. Unlike a sight glass, magnetic coupling allows the MLI to indicate liquid levels without direct contact between the externally-mounted visual indicator and the fluid in the vessel.

A magnetic field consists of imaginary lines of flux originating from the north and south poles and completely surround the magnet. This field acts on other objects (magnets or ferromagnetic materials) through these forces. When a magnetic field acts upon another body with sufficient force to influence it, the pair are said to be magnetically coupled to each other. In the case of a magnetic level indicator, the float is magnetically coupled to the indicator scale.

The MLI float, located inside the chamber and specifically engineered to provide proper buoyancy in the targeted fluid, dynamically tracks the surface of the liquid as it rises and falls. The magnet assembly inside the float generates a magnetic field that penetrates through the chamber wall to couple with the visual indicator.

Typical applications include:

• Alkylation units 
• Boiler drums
• Feedwater heaters
• Industrial boilers
• Oil / Water separators
• Process vessels
• Propane vessels
• Storage tanks
• Surge tanks
• Wastewater tanks

Advantages of the MLI

A magnetic level indicator is often used in applications where a sight glass (or glass sight gauge) is unsafe, environmentally risky, or difficult to see.

Typical shortcomings of glass sight gauges include:

• High pressures, extreme temperatures, deteriorating seals, and toxic or corrosive materials may cause a risk of fugitive emission of dangerous substances. 
• Some chemical materials within a process vessel or storage tank can attack the glass, causing discoloration of the sight gauge, thus decreasing level visibility. 
• Liquid/liquid interfaces can be very difficult to read in a sight glass particularly if the liquids are of similar color. Clear liquids can also be difficult to see in a sight glass. 
• Liquids that tend to coat or build-up on surfaces can hinder visibility by forming an opaque film on the glass. 
• To cover a large measuring span, sight glass assemblies typically must be staggered using multiple sections. 

Key reasons for selecting an MLI over a sight glass are:

• Improved safety due to the absence of fragile glass and a substantially reduced number of potential leak points. 
• Greatly increased visibility 
• Reduced maintenance. 
• Easier initial installation and addition of transmitters and switches without interrupting the process 
• Lower long-term cost of ownership and legitimate return-on-investment benefits. 
• Single chamber measurement over 20 ft. (6 m) without staggering chambers.

When using a transmitter in conjunction with a magnetic level indicator, consider using a wireless connection to deliver the process signal from the transmitter to the monitoring and control unit. Analynk has effective solutions that can be easily implemented. A video shows an application example.

Practical Considerations for Wireless Transmission of Industrial Process Control Signals

Industrial process signal transmitter

Rigging up the proper gear to establish wireless transmission of process measurement signals is generally a straight forward task. There are, however, a vastly different set of considerations than those for a wired transmission of the same signal. In order to select the right equipment for the job, some general comprehension of radio signals can be useful.

Radio wave frequencies are below the infrared range on the electromagnetic spectrum, thus their wavelengths are comparatively long. Three things can happen to electromagnetic radiation (radio waves) when encountering a barrier. 

• Reflectance: The wave bounces off the barrier.
• Transmittance: The wave passes through the barrier.
• Absorbance: The wave is stopped.

Which of the three possibilities will occur depends upon a number of factors relating to the signal and the barrier, some of which include:

• The wavelength of the radiation
• The intensity of the radiation hitting the barrier
• The chemical composition of the barrier
• The physical microstructure of the barrier
• The thickness of the barrier

Here is a conglomeration of knowledge items pulled together from a number of public sources that can be applied when considering a wireless installation.

Milliwatts (mW) are the common measurement unit of radio frequency (RF) power. A logarithmic scale of decibels, referencing 1 mW as the zero point, provides a useful way to express the comparative strength of RF signals. Using decibels, a signal strength of 1 mW is registered as 0 dBm. RF power attenuates according to a logarithmic function, so the dBm method of expressing RF power enjoys widespread use.

Industrial wireless communications applications in North America predominantly operate in either the 2.4 GHz or 900 MHz frequency range. Higher frequency will provide more bandwidth, but at the cost of reduced transmission distance and obstacle penetration. Lower frequency can require a larger antenna to attain the same signal gain.

Transmission power is not the only solution for delivering a signal. Low power signals can be successfully received by sensitive radio equipment. Reducing the data transmission rate can increase the functional sensitivity of the receiving equipment, too.

Be mindful of the existence or potential for RF background noise in your communications environment. A higher level of background noise can hamper the effectiveness of your equipment. The "noise floor" varies throughout the frequency spectrum and is generally below the sensitivity level of most equipment. Industrial environments can sometimes provide unusual conditions which may warrant a site survey to determine the actual noise floor throughout the communications area.

Weather conditions can impact signal transmission

Radio transmission is susceptible to environmental elements on a variable basis. Since the environment can change without notice, it is useful to know the fade margin of a wireless installation. Fade margin expresses the difference between the current signal strength and the level at which the installation no longer provides adequate performance. One recommendation is to configure the installation to provide a minimum of 10dB of fade margin in good weather conditions. This level can provide sufficient excess signal strength to overcome the diminishing effects of most weather, solar, and interference conditions.

There are a number of simple methods to determine whether an installation has at least a 10 dB fade margin. Temporarily installing a 10dB attenuator on the system antenna, or installing a length of antenna cable that yields 10dB of attenuation will allow you to determine if the installation can accommodate 10dB of environmental impact on the signal. If the system operates suitably with the attenuation installed, you have at least that much fade margin.

RF signals attenuate with the square of the distance traveled, so if transmission distance is to be doubled, then the signal power must increase fourfold. 

True “line of sight” signal paths are found in a limited number of installations. The number, type, and location of obstacles in the signal path can have a significant impact on the signal and contribute to what is referred to as path loss. Probably the simplest way to reduce the impact of obstacles is to elevate the antennas above them.  Obstacles, in almost every case, are affixed to the earth, so their interference is reduced by elevating antennas to “see” over the obstacles.  

Wooded areas can be a significant barrier

When the signal path extends through an outdoor area, weather conditions have an impact on the path loss, with higher moisture levels increasing the loss. Large plants, most notably heavily wooded areas, can impose substantial reduction on RF signals and may require elevating antennas above the trees or using repeaters to route the signal around a forested area.

Industrial installations routinely present many reflective obstacles in the signal path. The transmitted signal may reflect off several obstacles and still reach the receiving antenna. The received signal strength will be the vector sum of all the paths reaching the antenna. The phase of each signal reaching the antenna can impact the total signal strength in a positive or negative way. Sometimes relocating the antenna by even a small amount can significantly change the strength of the received signal.

Antenna cable 

Antenna cable contributes to signal attenuation. Use high quality cable of the shortest length possible to minimize the impact on performance.

Analynk Wireless has the equipment and expertise to help you deliver wireless process signals across the room, across the street, or across the globe.

Two-Wire vs. Four-Wire Transmitter For Analog Process Measurement and Control Signals - What Really Matters?

One of many form factors of two wire transmitters
for industrial process measurement and control
Courtesy Telmar Instruments

Transmitters are everywhere in process control. They take a sensor output signal,amplify and condition it, then send it to monitoring and decision making devices. The most common analog electrical signal used for transmitting process control signals is a 4-20 mA (milliampere) current flow. It has succeeded in its adoption for a number of reasons, not the least of which are its resistance to interference and ability to transmit a signal across a substantial length of cable.

Aside from the sensor connection, there are two basic wiring schemes for these devices. The simplest employs just two conductors to transmit the signal and coincidentally provide operating power for the transmitter electronics. This type of transmitter is commonly referred to as a "loop powered" or "two-wire" device. A DC power supply, typically 24 volts, is wired in series with the 4-20 mA output signal and the transmitter derives its operating power from this source. Loop powered devices generally consume very little power, but process designers must consider the total resistance imposed on the loop by all connected devices. The cable, unless the length is monstrous, poses a measurable but comparatively small resistance. Careful consideration should be given to the resistance imposed by receiving devices, especially if there are several in series, receiving the loop signal. The output voltage of the power supply and the maximum tolerable voltage of the connected devices will serve as limiting factors on loop instrument quantity. Where they can be applied, two-wire transmitters offer a straight forward solution for delivery of analog process measurement signals.

A "four-wire" transmitter gets its name from, you guessed it, the two pairs of wires used to provide operating power and a signal transmission path. Provided with a separate power source, possibly even 120 volts AC, this transmitter type will often be found in applications where the sensor may have power requirements that cannot be met with the limitations inherent in the loop powered device. While it may seem that the separate power supply negates the need to consider total resistance load on the signal loop, this is not the case. The signal loop still will be limited by the DC power supply that serves as the driving force of the loop.

In many cases, the question of "two-wire or four-wire" will be answered by the transmitter manufacturer. Since the two-wire scheme is a less burdensome installation, it may be the only product offering when a suitable device can be designed for an application. That said, a diligent search will probably find two and four-wire versions of transmitters for almost every application.

What are some decision making guidelines?

• Some types of transmitters have sufficiently high power requirements that they cannot be loop powered. In this case, four-wire may be the only option.
• For low resistance loads, use 2 wire transmitters for a simpler installation.
• Allow some headroom in the loop resistance to accommodate at least one added receiving device in the future. For example, a temperature signal may serve as an input to a controller now, but need to service a recording device potentially added in the future.
• Distance should not be mindlessly overlooked, but is generally not a limiting factor, as most installations would be compatible with the distance limitations for two- or four-wire device output signals. 
• When signal transmission distances become unwieldy, due to cabling costs or other factors, consider a wireless transmitter instead of a wired device.

The important aspect of applying 4-20 mA signal loops is to maintain the capability to add another receiving device to the circuit. The use of information in the form of process signals has been growing for a long time and is likely to continue. It is certainly easier to wire an additional device into an existing loop, than to install an additional sensor, transmitter, power supply, and cabling to accommodate the additional device. 

Analynk provides wired and wireless solutions for delivering analog process control signals. The wired devices carry the company's Telmar brand name. Wireless solution products carry the Analynk and Sensalynk brand name.

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Creating Wireless Process Connections Is ABC Simple

Industrial wireless is not new, it is a mature technology. With the products available today, implementing a wireless process signal connection is no more difficult than installing a simple process controller. Analynk is a part of that simplicity, manufacturing modular receivers, transmitters, and companion products enabling operators at any scale to effectively deploy a 900 MHz or 2.4 GHz wireless solution.

There are many instances where a wireless solution provides distinct advantages over wired installations. Understanding the simplicity of wireless installations, and that product based solutions are readily available, can unleash your ingenuity at solving process control challenges using wireless communications. A previous article may help you recognize opportunities to avoid expensive or difficult cabling, or actually make connections you thought were impossible.

Let's look at a basic installation that measures temperature at a remote location (the measuring station) and transmits the signal to your office (the monitoring station).

Here is all you need:

• Power supply to operate the temperature measurement instrument and the Analynk transmitter. Analynk transmitters consume little power and can be provided with photovoltaic power supplies, if needed.
• Temperature measuring device of your choice with 4-20 ma output signal and up to two discrete outputs. It does not need to be wireless. 
• Analynk transmitter located at the temperature measurement station to convert the 4-20 ma temperature signal to digital format and send it to the monitoring station. The connection between the temperature measuring device and the Analynk transmitter is wired.
• Analynk receiver located at the monitoring station to receive and decode the signal from the Analynk transmitter, converting it back to 4-20 ma. A wired connection between the receiver and your monitoring or recording equipment delivers the 4-20 ma temperature signal to its destination.

The simple wiring connections to the transmitter and receiver differ little from those of most other devices (see the ABC’s on the illustration).

A - Connect a power source to operate the unit
B - Connect the input signal (if it's a transmitter) or output signal (if it's a receiver).
C - Connect discrete inputs (if it's a transmitter) or outputs (if it's a receiver).

Wiring diagram for Analynk Model A753 wireless transmitter

Setting up the transmitter and receiver takes no more technical knowledge than other modern control devices. You follow instructions to set a few parameters, calibrate, and put the system into operation.

You can gang inputs and outputs together with an expander module and use a single transmitter and receiver to deliver multiple sensor signals. All units are DIN rail mounted with removable terminals for simple, organized installation and replacement.

Wireless connections can expand your operating capabilities, as well as business opportunities. Analynk has made the implementation easy. Use your creativity and ingenuity to bring new applications to your operation. Contact Analynk anytime to discuss your ideas or get the help you need to put your ideas into action.