How Wireless Sensor Networks Operate
Frequently Asked Questions
What is an OTC Wireless Sensor and I/O Network?
The OTC Sensor Network is designed for industrial automation applications to wirelessly monitor and control mission-critical processes around the clock, ensuring data is delivered more consistently and reliably. It helps eliminate trenching, permitting and reduces material, labor, and engineering costs, empowering operators to deploy data infrastructures much more quickly and efficiently than with a traditional hardwired system.
It is also known for its last-mile telemetry solution enabling operators to collect process data in hazardous locations and areas without access to a power grid. Its low-powered Wireless Gateways and I/O Modules along with self-contained Wireless Transmitters provide robust performance in harsh and hazardous environments.
The OTC Sensor Network is designed around point-to-multipoint and peer-to-peer network topologies. Wireless Gateways in the network are designed for collecting and mapping I/O points in the system as well as communicating with third-party master or slave devices over Serial or Ethernet connection. Each Wireless Gateway can support up to 63 Wireless Transmitters or Wireless I/O Modules utilizing point-to-multipoint or “star” topology. A network can have multiple Gateways for sharing data and mapping I/O point with each other using peer-to-peer or “distributed star” topology.
What is the difference between OTC Sensor and I/O Network and WIO System?
The OleumTech “OTC” Sensor and I/O Network is a star topology, point-to-multipoint and peer-to-peer advanced wireless system that utilizes a Wireless Gateway as a primary data collection point. The OTC Network adheres to Modbus and LevelMaster protocols for interfacing with third-party master or slave devices. The OTC Network is extremely flexible for distributing I/O virtually anywhere within its network, and is highly scalable, capable of having hundreds of sensor nodes in a same network.
The OleumTech WIO System stands for Wireless I/O System allowing quick and easy replacement of hardwires, eliminating costly trenching, permitting, and running conduit. It is a point-to-point, bi-directional system that only interfaces 0-10 V, 4-20 mA, and discrete signals. Input signals that come in on one end of the Radio Station, simply gets replicated on the other end as outputs, and vice versa.
The Wireless Gateways and other Class I, Div 2 Modules in the OTC Network, utilize 1 Watt radios whereas the WIO System utilize 250 mW radios in the 900 MHz ISM band.
The transmission rate in the OTC Network is anywhere between 1 second to 1 hour (user controlled).
The transmission rate in WIO System is anywhere between 100 ms to 1 second (based on number of I/O Modules and Tx mode).
What type of warranty does OleumTech provide for its products?
All products come with a 2-year warranty. Please reference the warranty page for details.
Is the OTC Wireless System scalable?
Each OTC Wireless Gateway supports up to 63 Wireless Transmitters or Wireless I/O Modules. Any site configuration will scale with the number of Wireless RTUs/Gateways. Furthermore, since this Wireless Sensor Network is based on a Peer-to-Peer networking platform, you can have multiple Wireless Gateways to share data across a same network. This advantage allows users to have multiple access points to critical data, aggregate data, and distribute control. This form of wireless data collection reduces the infrastructure and data communications costs.
900 MHz vs 2.4 GHz? Is the very popular 2.4 GHz frequency the way to go?
For a long range, high reliability 2.4 GHz band is not the best choice. For shorter range applications, the 2.4 GHz band has some advantages, such as using a smaller antenna than required by 900 MHz devices.
This often results in interference and poor operation for devices that compete in this frequency range; and many 2.4 GHz devices will not operate satisfactorily in the vicinity of other 2.4 GHz devices.
The biggest advantage of the 900 MHz band is the greater range (typically at least 10 times that of 2.4 GHz) and reduced attenuation from rain when compared to 2.4 GHz devices. The 900 MHz band is the best choice for the highest reliability, interference rejection and longest range in hostile, industrial environments.
What is intrinsic safety?
Intrinsic safety is a protection concept deployed in sensitive and potentially explosive atmospheres. Intrinsic safety relies on the equipment being designed so that it is unable to release sufficient energy, by either thermal or electrical means, to cause an ignition of a flammable gas.
Intrinsically safe is achieved by limiting the amount of power available to the electrical equipment in the hazardous area to a level below that which will ignite the gases.
In order to have a fire or explosion, fuel, oxygen and a source of ignition must be present. An intrinsically safe system assumes the fuel and oxygen is present in the atmosphere, but the system is designed so the electrical energy or thermal energy of a particular instrument loop can never be great enough to cause ignition.
Traditionally, protection from explosion in hazardous environments has been accomplished by either using explosion proof equipment which can contain an explosion inside an enclosure, or pressurization and/or purging which isolates the explosive gas from the electrical equipment. Intrinsically safe equipment cannot replace these methods in all applications, but where possible can provide significant cost savings in installation and maintenance of the equipment in a Hazardous area. The basic design of an intrinsic safety barrier uses Zener Diodes to limit voltage and resistors to limit current and a fuse.
Most applications require sending of signals out of or into the hazardous area. The equipment mounted in the hazardous area requires approval for use in or in conjunction with an intrinsically safe system. Any non-intrinsically safe barriers designed to protect the system require mounting outside of the hazardous area.
Intrinsic safety equipment requires testing and approval of an independent agency to ensure its safety. The customer should specify the type of approval required for their particular application.
What is ISM frequency?
Industrial applications typically operate in “license free” frequency bands, also referred to as ISM (Industrial, Scientific and Medical). No license is required to operate 900 MHz devices within the USA, and the FCC approves them. The frequencies and power of these bands varies from country to country. The most common frequencies encountered are:
- 2.4 GHz – nearly worldwide
- 915 MHz band – North America, South America, some other countries
- 868 MHz band – Europe as frequency rises, available bandwidth typically rises, but distance and ability to overcome obstacles is reduced. For any given distance, a 2.4 GHz installation will have roughly 8.5 dB of additional path loss when compared to 900 MHz.
Are there separate transmitters and receivers when it comes to wireless gateways?
No. Every Wireless Gateway is both a transmitter and a receiver or “transceiver.” The units are identical when it comes to RF radio, except for the configuration stored inside each unit – programmed using OleumTech’s Windows based BreeZ® Configuration Software tool.
How does OTC Sensor and I/O Network ensure RF data verification?
Yes, there is full data verification. Unlike competitors ‘one way’ or ‘report on an event’ type, these maintain continuous communication and are fully bi-directional so there are several ways to verify full and correct data transfer. OTC Wireless Devices internally handle error detection and retries for you – based on 16-bit cyclic redundancy check (CRC) value which is appended to data packet.
How is functional integrity of wireless communication achieved with the OTC wireless network?
Remote units report their status and diagnostics at timed intervals i.e Battery Voltage, RSSI, RF Timeout. So, Operators can check if any field unit needs replacement and for what reason.
How does receiver sensivity/data have impact on range?
The more sensitive the radio, the lower the power signal it can successfully receive, stretching right down to the noise floor. You can often improve your receive sensitivity, and therefore your range, by reducing data rates over the air. Receive sensitivity is a function of the transmission baud rate so, as baud rate goes down, the receive sensitivity goes up. Many radios give the user the ability to reduce the baud rate to maximize range.
The receive sensitivity of a radio also improves at lower frequencies, providing another significant range advantage of 900 MHz (vs. 2.4 GHz) – as much as 6 to 12 dB!
Solar Panel Operation - Can I just connect a 9-30 Vdc source directly to the wireless gateway to operate the device?
Normally in the field, a solar panel is hooked up to an external battery charging system. A Gateway can be indirectly connected to a solar panel in this manner that outputs 9-30 Vdc.
What is the true wireless range?
This is a very difficult question to answer, since it will vary in every installation. The actual range will depend on many factors, including the device location, height, shape of the terrain, terrain surface, obstacles, the antenna used, proximity to similar devices, radio power etc.
As a very general guideline in a typical, outdoor location, where each unit is visible from the other and using the internal antennas supplied with the standard product a range of at least 10 miles is to be expected, and 20 miles is usually possible. A similar ‘line of sight’ installation, using an external Yagi antenna at each end should produce a range of 40 miles.
What are sources for RF noise?
RF background noise comes from many sources, ranging from solar activity to high frequency digital products to all forms of other radio communications. That background noise establishes a noise floor which is the point where the desired signals are lost in the background ruckus. The noise floor will vary by frequency.
Typically the noise floor will be lower than the receive sensitivity of your radio, so it will not be a factor in your system design. If, however, you’re in an environment where high degrees of RF noise may exist in your frequency band, then use the noise floor figures instead of radio receive sensitivity in your calculations. If you suspect this is the case, a simple site survey to determine the noise floor value can be a high payoff investment.
What is spread spectrum signaling/modulation?
The term ‘spread spectrum’ covers a general method of transmission, where transmit and receive frequencies are constantly changing or ‘hopping’ through various channels. This method was devised as a means to allow many devices to effectively share a bandwidth.
There are several classifications allowed by the FCC to cover different devices and applications, these classifications also govern both the RF power and antenna systems that may be used. These classifications all use the generic term ’spread spectrum’ as a transmission method.
What is typical battery life of an OleumTech wireless transmitter?
One critical advantage of wireless is their independence from the wiring constraints and costs of traditional networks. This advantage will not materialize unless an adequate wireless power source is available, so power efficiency is a critical design factor. Our Battery-powered field end-node device operations can be pushed or set on timed intervals. At selectable intervals, the field device is “awakened,” the measured value is interrogated, and the field device switches off. Autonomous measuring stations are possible. Depending on time intervals, battery life can be several years.
But in no certain way can battery life be extended beyond the shelf life of the battery as specified by the manufacturer. It is the end user’s job to verify the wireless device specification against the battery vendors. Under typical remote monitoring applications 5 years is very common.
What is a fade margin?
Fade-margin is a term critical to wireless success. Fade-margin describes how many dB a received signal may be reduced by without causing system performance to fall below an acceptable value. Walking away from a newly commissioned wireless installation without understanding how much fade margin exists is the number one cause of wireless woes.
Establishing a fade margin of no less than 10dB in good weather conditions will provide a high degree of assurance that the system will continue to operate effectively in a variety of weather, solar, and RF interference conditions.
What is line of sight?
In a clear path through the air, radio signals attenuate with the square of distance. Doubling range requires a four-fold increase in power.
RF Radio manufacturers advertise “line of sight” range figures. Line of sight means that, from antenna A, you can see antenna B. Being able to see the building that antenna B is in does not count as line of sight. For every obstacle in the path, de-rate the “line of sight” figure specified for each obstacle in the path. The type of obstacle, the location of the obstacle, and the number of obstacles will all play a role in path loss.
Though not in the ISM bands, VHF and UHF models have much better coverage in non line of sight applications but they require licensing.
What makes OleumTech OTC wireless transmitters safe for industrial applications?
The OleumTech Wireless Transmitter design is Intrinsically Safe and designed for use in virtually all industrial applications, including hazardous environments. Majority of the Transmitters are certified for use in Class I, Division 1 (Zone 0) areas.
Which path loss scenarios must be taken into line of sight consideration?
While a few saplings mid-path are tolerable, it’s very difficult for RF to penetrate significant woodlands. If you’re crossing a wooded area you must elevate your antennas over the treetops.
Weather conditions also play a large role. Increased moisture in the air increases path loss. Usually, higher the frequency, the higher the path-loss tends to be.
Also be aware of the obstacles that are mobile. Wireless applications can be affected by temporary obstacles such as a stack of containers, a parked truck or material handling equipment.
Path Loss Rules of Thumb:
- To ensure basic fade margin in a perfect line of sight application, never exceed 50% of the manufacturer’s rated line of sight distance. This in itself yields a theoretical 6dB fade margin – still short of the required 10dB.
- De-rate more aggressively if you have obstacles between the two antennas, but not near the antennas.
- De-rate to 10% of the manufacture’s line of sight ratings if you have multiple obstacles, obstacles located near the antennas, or the antennas are located indoors.