At the heart of Permasense monitoring systems are sensors that employ well-proven ultrasonic wall thickness measurement principles. The sensors are battery powered and send the data wirelessly to their gateway, which enables that data to be viewed at desk.
The WT series sensors employ unique stainless steel waveguides that hold the ultrasonic transducers and electronics away from what could be a very hot piece of metal.
The waveguides are designed to transmit the ultrasound from the transducers without distortion yet reliably isolate the transducer and electronics housed in the (orange) sensor head from extremes of pipework temperature – up to 600 °C in refinery pipework and down to -180 °C in LNG facility pipework.
The waveguides guide the ultrasonic waves from the transducer to the pipe wall and back. The sensor does not require any couplant to transmit the ulttrasound from the sensor to the pipe wall.
The sensor acquires a number of ultrasonic wave pulses in the same way as any other ultrasonic wall thickness measurement methods – the first is a wave that travels via the surface; this is followed by the first backwall (inner pipe wall) reflection and a subsequent second backwall echo. The time difference and the ultrasonic wave velocity are then used to calculate (in the electronics in the sensor head) the thickness of the pipe wall.
Temperature compensation further eases data interpretation, maximising decision making speed and value
ET SENSOR SERIES
The ET sensor is specifically designed for quick and easy installation in lower temperature (up to 120 °C (250 °F)) applications. The sensor uses EMAT technology and is capable of measuring the metal wall thickness through external protective coatings. The ET series is therefore ideally suited to upstream applications, where the operating temperatures are generally lower than refineries and it is important to maintain the integrity of the external protective coating.
The thickness value – with associated waveforms (A-scans) – is sent via a wireless mesh network to a fixed gateway unit. There are two wireless protocols available to suit your needs and corporate policies: Permasense proprietary mesh protocol (100 series system) and Wireless HART (200 series system). Both wireles protocols operate in the 2.4 GHz Worldwide unllicenced band and use IEEE805.15.4 standard for robust and secure industrial wireless commmunication.
In both cases, the wireless mesh is self-forming, self-managing, and self-healing: thus neither cabling, nor any previously installed wireless infrastructure, is required prior to sensor installation. Each communication link (hop) between two devices can be up to 50m (160 ft) and there can be up to 8 hops between the farthest sensor and the gateway.
The sensors communicate via an ultra-low-power radio which enables multi-year battery life. This eliminates the need for (potentially expensive) access for battery replacement between planned periods of access to the sensor locations (e.g. shut downs or turnarounds).
The advantages of wirelessHART, as used by WT210 and ET210 systems, are valuable: