Wednesday, November 15, 2017

Comparison of 900 MHz vs 2.4 GHz for Industrial Wireless Connectivity

depiction of wireless process signal transmission in industrial setting
IOSelect provides equipment to establish wireless
process signal connections.
Image courtesy IOSelect
Wireless transmission of measurement and control signals are the future, and present, of process control. WiFi is already prevalent in higher density environments and providing benefits of reduced cabling and more. Wireless communications also can be used to connect devices over substantial distances, even globally. This article will focus on applications of moderate to long distance that will employ point to point communications of dedicated devices.

In establishing a wireless process signal connection between two points, an initial consideration will be whether to employ 900 MHz or 2.4 GHz as the radio band. There are some general implications associated with the selection.
  • Signal attenuation over any distance is greater for 2.4 GHz than 900 MHz. This generally means that 900 MHz can cover a greater distance and provide a signal of sufficient strength to properly communicate.
  • Atmospheric attenuation for either frequency band is about the same, with a very slight advantage to 900 MHz.
  • Both frequencies require "line-of-sight" to provide predictable and reliable operation. Obstructions within that zone can degrade the signal. Any obstructions with dimensions approximating the wavelength of the signal tend to have a greater impact. The wavelength of a 2.4 GHz signal is 12.5 cm (4.52 inches), 900 MHz is 33.3 cm (84.6 inches). 2.4 GHz signals are susceptible to interference by smaller objects in the transmission path than are 900 MHz signals.
  • Without getting too technical, the height of a 900 MHz antenna will need more elevation than that of a 2.4 GHz antenna in order to provide what is known as "free space propagation". This is related to the Fresnel Zone and has greater impact as transmission distance increases.
  • FCC rules allow larger transmit power ratings for 2.4 GHz radio signals than 900 MHz, increasing the potential range for 2.4 GHz.
Having a general understanding of the factors that vary between 900 MHz and 2.4 GHz and how they might impact your installation can lead to a better project outcome. Evaluate your potential installations with the above points in mind. Their impact on any particular application can vary depending upon the distance, topography, and potential obstructions. Share your wireless communications challenges with application specialists. Combining your site and process knowledge with their product application expertise will produce an effective solution.

Wednesday, November 8, 2017

Wireless Transmission of Industrial Process Control Signals - Practical Considerations

industrial wireless transmitter or receiver for process measurement and control
Establishing wireless process signal connections
requires consideration of a different set of factors
than a wired installation.
Image courtesy IOSelect
Establishing wireless connections for the 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.

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.

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

Share your connectivity challenges with application specialists, leveraging your own knowledge and experience with their product application expertise to develop an effective solution.

Friday, November 3, 2017

Programmable Automation Controller Flexes into Many Applications

programmable automation controller modular backplane
One of several programmable automation controller
backplane configurations for the T2750.
Image courtesy Eurotherm
The Eurotherm T2750 is a high performance modular control unit that provides redundancy and capability that are unmatched in a consolidated single unit. The controller backplane, of which there are several variants to accommodate the scope of I/O needed for a wide range of process applications, can be populated from an array of I/O and function modules providing a customized setup that closely matches project requirements.

Capabilities of the programmable automation controller include:
  • I/O Block
  • Communications
  • Signal Conditioning
  • Control
  • Timing
  • Logic
  • Math
  • Valve and Motor Control
  • Diagnostics
  • Recorder
  • More
There is much more to learn about the highly capable T2750 Programmable Automation Controller. For more information, share your process automation and control challenges with a product application specialist, leveraging your own process knowledge and experience with their product application expertise to develop an effective solution.

Tuesday, October 24, 2017

Pneumatic Volume Booster

pneumatic control system volume booster
Pneumatic control system volume booster replicates a control
signal with higher available air flow at the output.
Image courtesy ControlAir, Inc.
A volume booster is employed in a pneumatic control system to reproduce a low flow control signal with a higher regulated flow output pressure. It uses an unregulated input pressure to maintain a regulated output pressure under flowing and non-flowing conditions. Many applications exist, a common one being a valve actuator which may require a substantially larger air flow rate than can be delivered by the control signal. The volume booster will reproduce the pressure of the input signal at its output, but with a larger available flow rate available from an independent source.

The volume booster is connected to the air supply line, with the output routed to whatever device is to be controlled. The control signal to the volume booster originates at another device, such as a transducer, valve positioner or other control means.

This pneumatic input signal serves as the output pressure setpoint for the booster. The volume booster regulates the flow from the supply line to deliver the sepoint outlet pressure, while allowing the booster to flow the maximum volume of the supply line. Boosters may also be referred to as pilot-operated regulators, as your control or pilot signal maintains the outlet pressure control.

The regulated output of a pneumatic volume booster can be any of several options to match the driven device requirements.
  • A direct reproduction of the pneumatic control signal
  • A multiple of the pneumatic control signal 
  • A fraction of the pneumatic control signal
The volume booster ratio is the multiplier or divider of signal pressure to output pressure. For example, a 2:1 ratio means output pressure is 1/2 the signal pressure. Similarly, a 1:2 ratio would provide output pressure twice the signal pressure. The actual output pressure, regardless of the ratio, is limited by the supply pressure.

There is substantial flexibility in the configuration and variants of volume boosters, enabling selection of the right unit for every application. Share your pneumatic control system challenges with process automation specialists, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Tuesday, October 17, 2017

New Product - Pressure Regulator For Very Low Flow Applications

low flow high pressure regulator valve
The JRDL Series pressure regulator for very low flow applications.
Image courtesy LowFlow - Division of Jordan Valve
Jordan Valve, under their Low Flow brand name, released a new series of products to expand their already extensive J-Series line of pressure regulators and back pressure regulators.

The JRDL Series is a diaphragm operated pressure regulator intended for use in applications requiring very low flow rates.  Line sizes include 1/2", 3/4", and 1" (along with metric equivalents) with threaded, socket weld, or flange connections. The standard outlet pressure ranges extend up to 400 PSI, with custom configurations available. A host of possible configurations, seal materials, and options round out the offering.

More technical detail and illustration is provided in the datasheet included below. Share your fluid control challenges with valve specialists, leveraging your own process knowledge and experience with their product application expertise to develop effective solutions.

Thursday, October 12, 2017

Total Chlorine Analyzer for Water or Seawater Applications

total chlorine analyzer for water or seawater with cabinet open
Total chlorine analyzer for water and seawater application.
Image courtesy Emerson - Rosemount
Chlorine has many uses throughout commercial, municipal, and industrial processes. Managing chlorine levels is an important part of many process control applications. The measurement of total chlorine in a water or seawater sample is accomplished with the Rosemount TCL Total Chlorine System.

The cabinetized unit includes a sampling system, total chlorine sensor, and transmitter to deliver total chlorine measurement to a control and monitoring system. The cabinet is fabricated from fiber reinforced plastic, making it suitable for marine environments. The transmitter provides analog outputs for temperature and chlorine, with a range of industrial communications options available.

The unit contains enough reagent to last approximately two months. Acetic acid and potassium iodide are injected into the sample. The resulting depression in the sample pH allows total chlorine to react with the potassium iodide to form iodine. The sensor measures concentration of iodine, and the transmitter interprets and displays the level of total chlorine from that measurement. The transmitter also serves as the operator interface for diagnostics, calibration, and setup. Sensor maintenance is fast and easy. Replacing the membrane requires no special tools or fixtures. Simply place the membrane assembly on the cathode and screw the retainer in place. Installing a new membrane and replenishing the electrolyte takes only a few minutes.

More detail is provided in the datasheet included below. Share all your fluid analytic challenges with process measurement specialists. Leverage your own process knowledge and experience with their product application expertise to develop effective solutions.

Friday, October 6, 2017

Valves, Regulators, Steam Traps, and More for Sanitary Processing

Steriflow manufactures a broad range of fluid control and regulator products for use in sanitary operations, such as in the pharmaceutical, food, beverage, and cosmetic industries. The video provides a comprehensive overview of the various products available from Steriflow.

Share all your sanitary process fluid control requirements with process measurement and control specialists, leveraging your own knowledge and experience with their product application expertise for develop effective solutions.