Industrial wireless instrumentation is rapidly becoming the technology of choice for many industrial applications. It is defined as the merger of wireless sensor network (WSN) technologies with industrial field instrumentation and it has become increasingly popular in the process industries. In wireless Instrumentation, an autonomous battery powered sensor system that integrates wireless technology to enables remote sensor values to be reported to a central hub. The central hub can be a Field Gateway that interfaces to a PLC or RTU systems; or directly to Cloud SCADA host.
Wireless Instrumentation networks are used for monitoring of process or environment parameters when cabling is not feasible to connect the sensors due to cost or time constraints. Wireless instruments typically monitor a single process parameter or multiple process variables with a multi-variable transmitter.
Wireless Instrumentation is comprised of the Wireless Instrumentation Electronics and the Sensor. The Wireless Sensor Electronics Package contains the wireless communications equipment, battery system, and sensor interface housed in a weather proof package.
- Power source: In Wireless Instrumentation, devices are battery powered to provide rapid deployment with minimum installation costs. These battery powered systems are designed to operate from 1 to 5 years between battery changes.
- Wireless communication technology: Unlicensed Radio (900 MHz, 2.4 GHz), Cellular, or Satellite technology is used in Wireless Instrumentation. The ISA100.11a standard for industrial wireless systems is mainly followed. Another standard used is Wireless HART which uses the same 2.4 GHz frequency band, but is more limited in use.
- Unlicensed radio is typically used to provide communications from local instruments to a field gateway for use by a PLC/RTU.
- Cellular and Satellite technologies will direct communicate to a Cloud Host.
- Licences Free Wireless Networks allow connectivity up to 1/4 miles from the sensor to field gateway. Range of the sensor can depend on the TX power of the wireless sensor, the frequency, and RF obstructions.
- Cellular technologies are ideal for municipal water applications since there would be reliable cellular coverage. Satellite technologies will be deployed in remote industrial applications like oil and gas, pipelines, or mining where there may be no reliable terrestrial coverage.
- Instrumentation Signal Interfaces: The Wireless Instrumentation can be integrated to devices including sensor element or Wireless Sensor nodes that interface to standard analog ( 4-20 ma, 1-5 VDC), digital (contact closures) instrumentation signal levels or data protocol (RS485 Modbus, Hart).
- Sensors: Wireless Instruments may be supplied complete with the sensing element. This is common for wireless instrumentation for pressure, temperature, and level measurements. The function of the wireless sensor is typically to report the process variable to the PLC/RTU or SCADA and not perform control logic.
Industrial wireless instrumentation is being applied to a wide variety of applications today, which includes:
- Monitoring applications that track the status of equipment or a process state, such as temperature or vibration.
- Alerts and alarms that track the status of a process state, such as temperature, or a safety state, such as hydrocarbon gas level. Exceptions are reported to an operator for appropriate action.
- Control applications such as controlling valve movements, motor operations etc.
Above shown is a control loop where a process variable (PV) is send from a wireless instrument to the controller and the controller sends back manipulated variable (MV) to the final control element.
Above mentioned are the most common areas of application of wireless instrumentation. But it doesn’t mean that this technology can’t be used in other areas of application such as automated safety instrumented function. Even though above mentioned applications the ones being currently practiced and this technology hasn’t made big inroads in safety applications.
- Lower cost, especially when large numbers of instruments are installed.
- Manageability. When wired connections fail, they are typically complete failures that occur without notice. Wireless failures are usually transient, and those transient problems can mostly be avoided by preventative maintenance linked to wireless diagnostics.
- Flexibility. After a wireless system is installed, it is easy to add new wireless instruments and also to report more data from existing instruments using wireless adapters.
- Security. Wireless security extends to the field instrument and does not rely on physical security of the transmission medium. (Some fieldbus technologies assume that field wiring is secure and therefore have no cryptography on the field instrument.)
- Redundancy within a wireless network. Typically, a wired instrumentation relies on a single wire to each instrument, with various opportunities for failure. A well-designed wireless system has redundancy built in at all steps in the transmission chain without any failure-prone connectors. Field experience is demonstrating that a redundant wireless channel can be every bit as reliable as a non-redundant wired channel, particularly when wires are long and/or subjected to challenging conditions.
- Redundancy at the plant level. A wireless system can be used to add redundancy to wired reporting, with the same data reported through wired and wireless channels.
- Battery maintenance. Battery maintenance of wireless devices constitutes a factor that somewhat offsets wireless cost savings.
- Limited wireless instrumentation. Today, there is a limited range of available wireless instrumentation.
- Continuous sampling is required. In some cases, it is not technically feasible to sample and report process data continuously under battery power.
- Limited reporting rates. Wireless instruments and systems can be configured to support reporting as frequently as every second with a transmission latency of a fraction of a second. Sub-second reporting rates are not typically used for battery-powered instruments at this time.
- Spectrum management. Wireless instrumentation shares the radio spectrum with other systems and applications. Spectrum management generally needs to be considered when each new wireless system is installed, and should also be continuously monitored.
Industrial wireless instrumentation is widely becoming a norm nowadays. But there are still hesitancy towards this new technology platform. Through extensive theoretical analysis, laboratory experiments and pilot installations, it has become apparent that wireless instrumentation is ready for adoption at scale in non-critical monitoring applications. For control and safety systems, however, the currently available solutions have limitations which must be addressed through research and innovation before they are able to fulfil the more stringent requirements found in these types of applications.