Transmitting Multiple I/O Points Along A Single Signal Path

Analynk A16000 Expansion Module provides up to
16 I/O points for wireless transmission or reception.

Wireless transmission of process control signals is steadily increasing in prevalence throughout many industrial environments. The ease of implementation, with no long cable runs to plan, layout, install, protect, and maintain, allows wireless installations to fulfill application niches that may have been considered impractical in the past.

Analynk provides hardware that easily allows the transmission and reception of up to 16 I/O points using a single transmitter and receiver. The A16000 Expansion Module can be configured with up to four internal cards that accommodate various types of input and output signals. The process is similar to setting up the I/O on a PLC. Connect the process signals to the A16000, and the A16000 to one of Analynk's transmitter or receiver devices. Setup is straight forward and allows the installation to be operable in minimal time.

Share your wireless communications and signal transmission challenges with the experts at Analynk and get recommendations on how to best implement workable solutions.

Analynk Model A16000 RF Expansion Module from Analynk Wireless, LLC

Understanding Telecommunications Terminology

Industrial wireless communications can include satellites

If you are delving into wireless communications for process control operations and expect to go beyond the use of industrial Wi-Fi, you are likely to encounter some concepts and lexicon that may be unfamiliar. A source of recognized standard definitions for industry specific terms will serve as a useful tool for understanding the specifics of radio communications.

Federal Standard 1037C, entitled Telecommunications: Glossary of Telecommunication Terms was issued by the General Services Administration late in the last century. It was superseded in 2001 by American National Standard T1.523-2001, Telecom Glossary 2000, published by Alliance for Telecommunications Industry Solutions commonly known as ATIS). The current version of the ATIS Telecom Glossary is available for use by the public. Find the glossary website, with its search engine, and either type a term to search for in the box or browse the extensive listings in alphabetical order. It's easy to use and can help you sort out the meanings of some industry specific terms.

Analynk Wireless is a wireless communications equipment provider to the industrial process control sector. Contact the application specialists at Analynk and share your wireless communication challenges.

Screen shot of the glossary, showing search box in upper left area

Understand Fresnel Zones and Their Potential Impact On Your Process Signal Radio Transmission

Rendition of an ellipsoid, the representative shape
of a Fresnel zone

Most of us have been touched by wireless communications in the industrial process control setting. The majority of the installations are likely to be networks that operate similarly to the wireless network you may have in your home. Multiple points communicate through a network controller of some sort. The facility is flooded with signal coverage through multiple access points, so there may not be much need to consider signal propagation. Of course, this is an oversimplification. The point to be made is that, as an operator or implementer, making the actual signal connection is probably not going to be an issue in most cases.

How would you approach an application with a one mile transmission distance?

Antennas with three Fresnel zones depicted and
obstruction that is outside the primary Fresnel zone
Courtesy Wikipedia

An extended transmission distance across an outdoor area requires more understanding of signal propagation and the factors that can impede the successful delivery of your
process data from transmitter to receiver. One concept that may come into play is the Fresnel zone.

I shall avoid any deep or technical approach to Fresnel zones, as my purpose is to provide the designer, technician, or implementer, who may have limited radio expertise, familiarity with the subject at a level empowering visualization of the concept to recognize the potential for its impact upon achieving a successful project. That said, a Fresnel zone, of which there an infinite theoretical number, is an ellipsoid shaped area extending between transmission and receiving antennas.  While we often consider the transmission path between two points as the popular "line of sight", an unobstructed straight line, radio frequency transmission is more accurately characterized by Fresnel zones. Being aware of the shape of the first, or primary, Fresnel zone for your application is an important element in identifying potential obstructions. A general practice is to keep the primary Fresnel zone at least 60% clear of signal obstructions, in order to maintain high wireless link performance.

There are numerous sources of Fresnel zone calculators online, but a strong recommendation to consult with your selected wireless equipment provider is in order here. Combine their expertise at applying their products with your application knowledge to reach the best outcome.

Introduction to Level Measurement

In many industrial processes, the measurement of level is critical. Depending on the nature of the material being measured, this can be a simple or complex task. Several different technologies for sensing level are briefly explained here.

Level Gauges or Sightglasses

Sight Glass or Gauge

The simplest form of level measurement for direct measurement of level (almost always visually) in a vessel. A level gauge (sightglass) is usually a clear tube connected to the a vessel at the highest and lowest part of the level range. The fluid level inside the vessel will be at the same hight as the level in the tube.

Floats

Float level indicator

Another very simple approach to level measurement for fluids or solids is the float. The float sits on
top of the material being measured and is visually, magnetically, or electronically located and equated to the level inside the vessel. It is important that the float material be compatible with the process media and that it freely moves on top of the process.

Hydrostatic Pressure

Hydrostatic Level

A very popular way to measure level because of the ease in equating the pressure of a fluid column with the level inside the vessel. In it's simplest form, a pressure sensor (gauge or transmitter) is attached to the bottom of a vessel and measures the pressure of the column. This pressure reading is then interpreted as level.

Bubbler Principle

Bubbler Systems

A variation of the hydrostatic pressure method, bubbler systems measure the pressure of a purge gas being injected into the fluid in a vessel through a dip tube. This approach comes in handy when sensing the level of corrosive fluids. The principle of operation is that the amount of pressure to "push" an inert purge gas through the dip tube will change according to the level in that vessel, and therefore can be correlated to the level.

Displacer Level

Displacer Level

Based upon the laws of buoyancy, a float (either inside its own isolated cage, or hanging in the process directly) is calibrated the the level of the fluid being measured. The displacer is usually a sealed metal tube and hang's in place in the process media. As more of the displacer’s volume becomes submerged, the buoyant force is increased on the making the displacer "lighter".

Echo level measurement

Echo (Ultrasonic, Radar, Laser)

Level measured by bouncing some wave form (sound, light, electromagnetic) off the surface of liquids and measuring their time of flight.

Capacitance level measurement

Capacitance Level

Capacitive level instruments measure the electrical capacitance of a conductive rod inserted vertically into a process vessel. As process level increases, the capacitance between the rod and the vessel walls increases, causing a signal change in the instruments circuitry.

Weight

Level is measured by knowing the empty weight of a vessel and the full weigh of a vessel and calibrating the points between. The shape of the vessel is can also be a factor.

Industrial level control requires deep knowledge and understanding of many process variables, such as media compatibility, interfaces, head pressures, material densities, and mechanical considerations. It's always recommended that an experienced consultant be involved with the selection and implementation of any industrial level device.

Image attribution: courtesy of "Lessons In Industrial Instrumentation" by Tony R. Kuphaldt

Understand Petroleum Refining for Better Process Control Support

Oil refineries can have different specialties and function

The petroleum refining industry provides an expansive market for process measurement and control instrumentation and equipment, valves, and process analyzers. Having a basic understanding of the industry can help purveyors of instrumentation and equipment properly address customer needs, as well as recognize where opportunities may lie. Here is a summary of the types of plants and processes.

Petroleum refineries produce liquefied petroleum gases (LPG), motor gasoline, jet fuels, kerosene, distillate fuel oils, residual fuel oils, lubricants, asphalt (bitumen), and other products through distillation of crude oil or through re-distillation, cracking, or reforming of unfinished petroleum derivatives.

There are three basic types of refineries:

• Topping refineries
• Hydroskimming refineries
• Upgrading refineries (also referred to as “conversion” or “complex” refineries). 

Topping refineries have a crude distillation column and produce naphtha and other intermediate products, but not gasoline. There are only a few topping refineries in the U.S., predominately in Alaska.

Hydroskimming refineries have mild conversion units such as hydrotreating units and/or reforming units to produce finished gasoline products, but they do not upgrade heavier components of the crude oil that exit near the bottom of the crude distillation column. Some topping/hydroskimming refineries specialize in processing heavy crude oils to produce asphalt.

The vast majority (75 to 80 percent) of the approximately 150 domestic US refineries are upgrading/conversion refineries. Upgrading/conversion refineries have cracking or coking operations to convert long-chain, high molecular weight hydrocarbons (“heavy distillates”) into smaller hydrocarbons that can be used to produce gasoline product (“light distillates”) and other higher value products and petrochemical feedstocks.

Figure 1 provides a simplified flow diagram of a typical refinery. The flow of intermediates between the processes will vary by refinery, and depends on the structure of the refinery, type of crude processes, as well as product mix.

Figure 1 - Refinery Flow Diagram
Wikipedia - www.en.wikipedia.org/wiki/Petroleum_refining_processes

The first process unit in nearly all refineries is the crude oil or “atmospheric” distillation unit. Different conversion processes are available using thermal or catalytic processes, e.g., delayed coking, catalytic cracking, or catalytic reforming, to produce the desired mix of products from the crude oil. The products may be treated to upgrade the product quality (e.g., sulfur removal using a hydrotreater).

Side processes that are used to condition inputs or produce hydrogen or by-products include crude conditioning (e.g., desalting), hydrogen production, power and steam production, and asphalt production. Lubricants and other specialized products may be produced at special locations.

Temperature Measurement: Thermistors, Thermocouples, and RTDs

This post explains the basic operation of the three most common temperature sensing elements - thermocouples, RTD's and thermistors.

A thermocouple is a temperature sensor that produces a micro-voltage from a phenomena called the Seebeck Effect. In simple terms, when the junction of two different (dissimilar) metals varies in temperature from a second junction (called the reference junction), a voltage is produced. When the reference junction temperature is known and maintained, the voltage produced by the sensing junction can be measured and directly applied to the change in the sensing junctions' temperature.

Thermocouples are widely used for industrial and commercial temperate control because they are inexpensive, sufficiently accurate for many uses, have a nearly linear temperature-to-signal output curve, come in many “types” (different metal alloys) for many different temperature ranges, and are easily interchangeable. They require no external power to work and can be used in continuous temperature measurement applications from -185 Deg. Celsius (Type T) up to 1700 Deg. Celsius (Type B).

Common application for thermocouples are industrial processes, the plastics industry, kilns, boilers, steel making, power generation, gas turbine exhaust and diesel engines, They also have many consumer uses such as temperature sensors in thermostats and flame sensors, and for consumer cooking and heating equipment.

Coil wound RTD element
(image courtesy of Wikipedia)

RTD’s (resistance temperature detectors), are temperature sensors that measure a change in resistance as the temperature of the RTD element changes. They are normally designed as a fine wire coiled around a bobbin (made of glass or ceramic), and inserted into a protective sheath. The can also be manufactured as a thin-film element with the pure metal deposited on a ceramic base much like a circuit on a circuit board. 

Thin-film RTD element
(image courtesy of Wikipedia)

The RTD wire is usually a pure metal such as platinum, nickel or copper because these metals have a predictable change in resistance as the temperature changes. RTD’s offer considerably higher accuracy and repeatability than thermocouples and can be used up to 600 Deg. Celsius. They are most often used in biomedical applications, semiconductor processing and industrial applications where accuracy is important. Because they are made of pure metals, they tend to more costly than thermocouples. RTD’s do need to be supplied an excitation voltage from the control circuitry as well. 

The third most common temperature sensor is the thermistor. A thermistor functions similarly to a RTD in that it exhibits a change in resistance associated with a change in temperature. A difference between the two is that, instead of using pure metal, thermistors use a very inexpensive polymer or ceramic material as the resistance element. The practical application difference between thermistors and RTD’s is the shape of the resistance curve for the devices. The RTD is linear, whereas a thermistor is non-linear, making it useful only over a narrow temperature range. 

Thermistor bead with wires
(image courtesy of Wikipedia)

Thermistors however are very inexpensive and have a very fast response. They also come in two varieties, positive temperature coefficient (PTC - resistance increases with increasing temperature), and negative temperature coefficient (NTC - resistance decreases with increasing temperature). Thermistors are used widely in monitoring temperature of circuit boards, digital thermostats, food processing, and consumer appliances.

How To Protect Wired Equipment From Lightning Strikes

There are methods to protect process control
equipment from lightning strikes

Lightning, though visually and audibly fascinating, is a high risk environmental factor for process measurement and control equipment. Recent advancements in the study of this natural occurrence have significantly increased general understanding of the source and path of a lighting strike, granting some additional insight into mitigating the risk to electronic equipment associated with lightning activity.

The abstract included below provides a useful synopsis of grounding, surge protection, and other methods for providing levels of protection from lightning strikes. Of particular interest is the concept of lightning ground potential rise (L-GPR) and how it can be used to predict an impending lighting event.

The predictive technology, combined with automated disconnection of the protected equipment from the AC power service can provide superior protection against damage caused by lighting strikes. Browse the paper below, as it is concise, illustrated, and will improve your understanding of lightning and how it impacts industrial process control equipment.

More information and consultation on enhancing your level of lightning protection is available from Analynk Wireless.

Lightning Protection Considerations for Wired Systems from Analynk Wireless, LLC