Improving Safe Operations with Wireless Vibrating Fork Level Switches

Level measurements can be some of the most important measurements for the safe operations of applications such as tank farms, boilers, pump control and more. Level measurement is a key part of monitoring and control strategies as well as safety instrumented functions.

In a Process Worldwide article, How Wireless Vibrating Fork Frequency Monitoring Improves Process Safety, Emerson’s Marianne Williams describes the use of these level switches to reduce operational risks.

Wireless-Vibrating-ForkVibrating fork technology has long been proven and:

…extensively used by operators in the switch’s various primary roles, which include mission-critical overfill protection, fail-safe high and low level detection, and pump control and protection.

Besides measuring the level, these devices provide frequency monitoring, used to monitor density changes in the fluid.

A piezo-electric crystal oscillates the forks at their natural frequency and any changes to this frequency are continuously monitored. The frequency of the vibrating fork changes depending on the medium it is surrounded by. The denser the medium, the lower the frequency.

In its normal operation as a switch, the output changes whether the tuning fork is wet or dry. By switching states, an alert can be sent to the operators of a low-level or high-level condition.

Because the frequency changes with fluids of varying densities, this means that:

…you can accurately distinguish between fluids of differing properties, say, oil and water, or acid and water, at a given point in the production process, which provides measurable benefits.

For many processes with tanks and vessels in remote areas without existing wiring infrastructure, wireless vibrating fork level switches can be easily added. These added measurements can reduce the exposure of plant personnel manually collecting these level readings in hazardous locations.

Marianne shares two applications for these wireless level switches—a decanting process and helping to meet safety and environmental directives. In the decanting example, a batch process stores acid with a layer of water on top to maintain stability. The decanting process must remove the stabilizing water or it will ruin the batch.

The existing solution was:

…for operators to visually monitor the phase change through a site glass in a pipe spool piece, radioing their control room to turn off a valve to stop decanting. This process obviously contained the potential for human error and consequent huge variations in batch consistency, and well as implications for operator safety and overall personnel productivity.

Level measurement technologies such as radar and magnetostrictive were considered but had limitations in suitability for the fluid types and successfully determining the interface level between acid and water. Vibrating fork technology was able to:

…accurately and immediately distinguish between water and acid provided reliable information of the phase change.

This change from manual to continuous measurement improved batch consistency and reduced time spent in hazardous locations.

Read the article for the second example of how an oil & gas company located within the jurisdiction of European Union floating roof tank directives was able to continuously monitor for floating roof tilt to reduce operational risk and comply with the regulations.

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

Posted Wednesday, June 29th, 2016 under Level.

One comment so far

  1. Once the wireless sensor network is in place there are several measurements on the storage tank and around the tank farm that can be done to improve the operations of the tank; reducing downtime and minimizing overfills and inadvertent product mix during loading etc. See further explanation in this article: Modernizing Old Tank Farms to Meet New Requirements.
    Many terminals and refineries are already doing this. Request a plant modernization audit to learn what can be done for your tank farm.

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