- August 01, 2017
- Emerson Automation Solutions
By Marianne Williams, Emerson
This article explains how the latest generation of vibrating fork level switches feature increased health monitoring functionality, which enables maintenance to be planned and process availability to be increased
By Marianne Williams, Marketing Manager, Emerson
Improved maintenance practices can help make significant gains in terms of plant and operator safety, production availability, efficiency, and subsequently profitability. By reducing scheduled and unscheduled downtime, companies can significantly reduce their maintenance spend. Optimised reliability practices - such as increased condition monitoring and analysis-based predictive maintenance activities - drive down operating costs and improve product or batch quality, health and safety, and environmental compliance.
The availability of low-cost sensors and wireless networks is helping to monitor the health of a larger amount of plant equipment online, such as pumps and separators. Previously only the most ‘critical’ equipment (failure of which results in an immediate production or processing outage) would receive such attention, but modern pervasive sensing strategies mean that this is now extended to ‘essential’ equipment (affecting process efficiency). Equally, the improved diagnostic capability of the latest measurement and control devices is ensuring that they don’t become a weak link.
Failed or poorly-performing measurement and control devices can have a detrimental effect on safety and process efficiency and therefore they themselves must be monitored. Supporting these efforts are devices that feature advanced integrated diagnostic capabilities which help maintenance teams to identify impending problems earlier, and remove the need for routine operator rounds, where manual visual checks are made. For devices used in critical monitoring and control applications, increased diagnostic capability is becoming very desirable. Operators want to spot an impending problem and know if a device may fail and why, so that appropriate remedial measures can be taken and potential downtime avoided.
Failed or poorly-performing measurement and control devices can have a detrimental effect on safety and process efficiency and therefore they themselves must be monitored. Should an instrument fail unexpectedly this may require the process to be stopped whilst the device is repaired. As with equipment failure, an unexpected device failure tends to be much more expensive to resolve than a planned repair, and there is also the potential for an unexpected failure to cause costly equipment damage and maybe even lead to a serious safety incident. If potential problems can be diagnosed early, before a failure occurs, then problems can be avoided and maintenance can be scheduled during a planned period of downtime, reducing costs.
Vibrating fork switches
Vibrating fork level switches are used in critical level monitoring and control applications such as high- and low-level alarms, including overfill prevention in safety instrumented systems applications. A switch failure can have serious consequences, as it could potentially lead to an overspill from a tank or vessel, and perhaps a subsequent environmental and/or safety incident, or perhaps a pump running dry and causing mechanical damage or risk of dangerous overheating. It is therefore vital that switches operate reliably, and that should a problem exist, it is recognised as quickly as possible.
Vibrating fork level switches are also now widely used in applications to increase process efficiency, for example in storage or separator tanks, ensuring that the fluid inside is kept at the optimal level to maximise capacity.
Vibrating forks are regularly replacing mechanical and float-based devices in plant upgrades because they require minimal maintenance and are very reliable as well as being compact, light in weight and easy to install. Despite being immersed in a tank or pipe and coming into contact with the liquid within, the shape of the fork ensures that a sticky or viscous liquid doesn’t attach itself to the device and drains away quickly. In addition, vibrating forks have an advantage over other level switch technologies in that they do not have moving parts that can freeze or get stuck, which increases their reliability and makes them virtually maintenance-free. There are, however, certain things that can affect the performance of these devices, such as electrical failure, build-up of material between the forks, corrosion and possible damage to the forks or sensor. To enable these issues to be flagged up early should they occur, some vibrating fork level switches are equipped with different diagnostics tools which constantly monitor the device ‘health’ and can alert to an emerging issue, ranging from basic status indicators through to analysis tools that constantly monitor operating parameters and instrument performance over its lifetime in service.
For example, some basic vibrating forks enable the status of the device to be accessed locally using a visible ‘heartbeat’ LED that can indicate various status conditions - including output status, calibration, internal electronics failure and load fault. In the event of a fault condition, the load is handled in a safe manner and the LED is pulsed at a special rate to show that a fault has been detected.
Using HART communications, the latest generation of vibrating forks can provide greater diagnostic functionality, enabling the device’s electronic and mechanical health to be monitored continuously. HART switches don’t merely give an on/off output – they have a number of other HART variables measuring different device parameters. This information can be accessed either directly, via connection to the device’s HART terminals, or from the control room through wired or wireless communication, using the HART network. Accessing this data from the central control room eliminates the need for field trips to interrogate each device, therefore increasing worker efficiency and safety. This is especially the case at plants with multiple measurement points, or with storage or process vessels which require operators to work at height or within hazardous areas to access instrumentation.
Emerson’s Rosemount wired and wireless vibrating fork liquid level detector, for example, uses HART communications to enable enhanced instrument health monitoring diagnostics that can detect external damage to the forks, internal damage to the sensor, corrosion and over-temperature. A unique frequency analysis function enables any media build-up, fork blockage or excessive corrosion to be detected immediately by a change in the fork sensor frequency over time. This provides operators with an indication that maintenance of the device may soon be needed and gives them the opportunity to schedule it during a period of plant downtime, to minimise process interruption and save money.
Emerson's Rosemount 2160 Wireless Level Detector
Another new and unique diagnostic tool enables operators to identify any potential problems with internal components and circuitry by monitoring the current and voltage drawn over the device lifetime. Any unusual behaviour which may indicate an emerging issue, such as internal corrosion, is signalled. This power advisory functionality provides a significant benefit for plant managers, as internal corrosion can lead to intermittent or complete loss of power to the device. If the device is no longer operational this can cause process downtime, lost revenue or possibly even damage to important equipment such as a vital pump.
For installations within safety instrumented systems, a fully integrated unique remote proof-testing capability now eliminates the need for workers to climb on top of the vessel to extract the switch from the process. This greatly reduces the time required to perform the procedure, increasing process availability, worker safety and efficiency.
Furthermore,WirelessHART has not only extended the range of applications for vibrating forks, but has also enabled remote access to advanced diagnostics that previously would have been unavailable, for example in inaccessible locations or where power is limited. User-configurable variables which can be monitored include output state, fork frequency, electronics temperature, and supply voltage. These can be configured for rising or falling values, and a limit can be set that will trigger an alert. There is also the provision to apply a dead band, switching delay, media density selection or hysteresis to optimise switching reliability.
Vibrating fork level switches provide plant managers with an effective means of detecting whether liquid is present or not in their tanks and pipes. More companies are turning to automated level measurement solutions, and devices are now capable of delivering more status and diagnostics information than ever before. Latest generation devices - both wired and wireless - provide advanced diagnostics that can flag up potential problems. This enables managers to resolve them during periods of planned downtime, before they can cause equipment damage or a safety incident and have a negative impact on the plant’s productivity.Learn More
Did you enjoy this great article?
Check out our free e-newsletters to read more great articles..Subscribe