Level Switches in Tank Overfill Safety Applications

Level measurements, especially in safety critical applications such as tank overspill protection, continue to advance in capability, accuracy and reliability.

Emerson's Marianne Williams

Marianne Williams
Marketing Product Manager

In this 3:16 YouTube video, Prevent overfills & decrease operating costs with Rosemount 2100 vibrating fork level switches, Emerson’s Marianne Williams shares how the Rosemount 2100 series of liquid level switches help solve measurement challenges by providing reliable overfill protection on tanks.

And, if you’ve been following the news lately in the U.S., tank levels are reaching storage limits, making accurate and reliable measurement’s paramount.

Marianne opens the video noting how safety regulations dictate the need for overspill protection on tanks. She notes that best practice is to install a liquid level switch as a backup to continuous liquid level measurement. The level switch is a second layer of protection for high- and low-level alarms.

The Rosemount 2100 series is a range of vibrating fork level switches that Marianne describes. Vibrating fork technology uses the principal of tuning fork vibration. When a tuning fork is struck, it vibrates. This vibration occurs at what is known as the forks ‘natural frequency’. This frequency will vary depending on the relative size, shape, and material of the forks.

The forks are driven to their natural frequency of oscillation by a piezo-electric crystal. Changes to this frequency are continuously monitored. The frequency of the vibrating fork sensor changes depending on the medium (liquid) in which it is immersed. The denser the liquid, the lower the frequency.

When used as a low level alarm, the liquid in the tank or pipe drains down past the fork, causing a change of frequency that is detected by the electronics and switches the output state (wet-to-dry). When used as a high level alarm, the liquid rises in the tank or pipe, making contact with the fork which then causes the output state to switch (dry-to-wet).

She notes that the Rosemount 2120 and Rosemount 2130 are SIL2-certified to IEC 61508 as required by IEC 61511 and SIL3 capable. The Rosemount 2110 level switch is a compact model for use in small vessels and pipes.

The Rosemount 2160 is the first wireless level switch and has also been TÜV-tested and approved for overfill protection according to the German DIBt/WHG regulations. This switch works well for monitoring and critical alarm duty applications where additional wiring would be costly and difficult.

All of these models handle difficult level conditions such as turbulence, foam, vibration, coating or changing liquid properties. Also, they require no calibration and minimum installation effort and ongoing maintenance.

Marianne closed noting that these switches provide a key complement to continuous level measurement such as guided wave and non-contacting radar.

You can connect and interact with other level measurement experts in the Level group in the Emerson Exchange 365 community.

2 comments

  1. Usually there are no spare wires running to the top of the tank so adding a secondary level detection switch becomes a lot easier using wireless. Learn more here:
    http://www.ceasiamag.com/article-7425-switchingtowireless-LogisticsAsia.html

    Once a wireless gateway is installed in the tank farm, there are many other measurements that can be done around the tank. This includes for instance measuring tank blanketing pressure to detect any issue with that. Other measurements, over and above product level/inventory, include for instance Floating roof tilt, Dyke valve position, Hydrocarbon leak, Sump pit level, Floating roof water pooling, and Transfer valve position line-up etc. See further explanation in this article:

    Instrumental to Success
    http://www.ceasiamag.com/article/instrumental-to-success/11137

  2. Use automated overflow equipment to your tank to prevent from overfill. This equipment will give sound as alarm when tank is over or empty.

Leave a Reply