Wireless gas detection
July 2017, System Integration & Control Systems Design
WirelessHART technology is based on the known and proven HART protocol. It combines this protocol with mechanisms to ensure that the reliability and detection range of wireless communication meet the high standards of process automation.
It is simple to integrate WirelessHART products, and integration in the host is performed in the same way as wired HART devices. This makes it easier for the customer to install, operate and maintain WirelessHART networks.
Nowadays, WirelessHART installations are increasingly used in plants for asset management, including preventive maintenance and system monitoring. They contribute to planned service and maintenance tasks to reduce system downtime and increase competitiveness. In addition to the well-known battery powered adaptors that work completely autonomously, there are loop powered WirelessHART adaptors that can be connected at any point in the 4 … 20 mA current loop. Power can also be provided via a 24 V supply or even using a solar panel as an energy source. The Bullet can be used in temperatures down to -40°C, a decisive argument in the equipping of an outdoor gas leakage detection system in a Canadian chemical company, for example.
Monitoring of gas limit values
The city of Sarnia in the southwestern part of the province of Ontario in Canada has a large number of production sites and refineries within the chemical and mineral oil industries. One of the companies based there has designed a comprehensive system for leakage detection for its entire site. Its goal is to detect gas escaping through leaks at an early stage. Depending on the type and diffusion behaviour of the gas, catalytic, electrochemical, infrared and solid-state sensors are used.
To pinpoint the location of detected leakage as precisely as possible, each of the 12 measuring stations, installed approximately 300 metres apart, are equipped with four gas sensors and a wind direction and wind speed sensor. Two of the gas meters use the 4 … 20 mA signal for transmission, while the other two are connected as HART field devices via multidrop to a Bullet. Therefore, a total of five Bullets are used per monitoring station for wireless, digital data transfer: one adaptor for each of the analog field devices, as well as an adaptor that uses the multidrop feature to transfer the signals of the two HART transmitters. These stations are not powered via the usual loop supply used by the Bullet, but via a battery pack that is charged via a solar panel.
The measuring stations have been installed at -20°C, and the operating temperatures can be as low as -33°C according to Canadian climate data. On the basis of known operating data and status data for the distribution infrastructure of the plant, the early warning measuring points were placed where potential leak points were either likely or difficult to reach for monitoring purposes. At the same time, the WirelessHART adaptors form a self-organising network. The large transmission distance and redundancy-related high transmission security ensure reliable connection and crosslinking of all participants in the leakage early warning system. The placement of the measuring points ensures that each of the potential escaping gases is reliably detected before it is dispersed or evaporated. The adaptors then ensure the signal transmission without delay as well as the alarm in the control room.
The engineering of the installed Bullets with maximum levels of robustness is impressive. The easy-to-clean aluminum housing is also suited to the harsh Canadian environmental conditions. It encapsulates all electronic components, including the antenna, and is thus extremely well protected against any possible damage. The special design also ensures that no static charging of the adaptor can take place, for example when cleaning.
In this application, the WirelessHART technology is responsible for plant monitoring, with better information about the plant status leading to early detection of unusual parameters and thus contributing significantly to cost savings, since a timely response is possible.
Mobile mixing tanks
A completely different application for the Bullet can be found in the chemical and pharmaceutical industries. Material buffers, preparation containers, dosing reservoirs – mobile mixing tanks with an integrated agitator – are used in process engineering processes, including a whole host of tasks. They are often part of a monitored process chain in critical procedures requiring monitoring, and in such cases are equipped with sensors.
In this specific application, the mobile tanks are equipped with a power supply to operate the agitator. To obtain information on the contents of the tanks, they are equipped with 4 ... 20 mA and HART-capable sensors for control of the drive speed of the agitator, of temperature and pressure in the container, as well as the pH value and the filling level of the medium. A WirelessHART adaptor like the Bullet is ideal for this application for various reasons. Through the existing power supply of the motor, the Bullets and field devices can be powered directly from this power source. At the same time, data from the field devices is transferred wirelessly to the control system to guarantee the mobility of the rolling mixing tanks.
The multidrop feature is also used for this application. There are a total of two adaptors installed per tank: one for the 4 … 20 mA signal of the agitator drive and one for the HART signals of the remaining four sensors. This application demonstrates the high level of robustness of the adaptors. They are designed such that they also withstand regular CIP cleaning processes, and as a result offer permanently high availability.
Ideal for the wireless integration of field devices
Whether widely distributed in the field or used for mobile applications, the WirelessHART adaptors in the Bullet product family allow wireless communication of measuring data, diagnostic data and parameterisation data for new or already wired field devices. Their application ensures satisfaction, since various explosion protection needs are covered, and 4 … 20 mA as well as HART field devices are compatible. The robust, industry-compatible design ensures a high level of availability for data transfer. The simple way of adding additional measuring points in the WirelessHART network makes these adaptors a future-proof investment.
Direct, pressure-resistant WirelessHART connection
The Bullet is the only WirelessHART adaptor on the market that, in addition to a standard variant and an Ex i variant for Zone 0 and Zone 20 and Class I, Div. 1, is also available in an Ex d enclosure for hazardous areas up to Zone 1 or Zone 21 and Class I, Div. 1. The Ex d encapsulated variant allows the simple integration of pressure-resistant encapsulated field devices into a WirelessHART network. This is because the Bullet can be installed directly or via a conduit on the Ex d field device or on a terminal box.
In Ex d-to-Ex d configurations such as this, devices and all components on the adaptor side that can cause ignition are installed in enclosures equipped with corresponding cable ducts. These enclosures are able to withstand the internal explosion pressure that could occur. As a result, it is not necessary to restrict current and voltage in the design of an intrinsically safe circuit or use Zener barriers to such an extent that the minimum ignition energy and ignition temperature of an explosive mixture are not reached. There is also no need to install the adaptor outside of the explosion-hazardous area, especially as there is no risk of electrostatic charge. The aluminum enclosure of the B not only meets requirements in terms of explosion protection, but is also designed for use under the harshest mechanical and environmental conditions.
For more information contact Pepperl+Fuchs, 087 985 0797, firstname.lastname@example.org, www.pepperl-fuchs.co.za