How long has it been since you looked at your liquid level measuring applications? Are you using the most effective current technologies, or making do with older approaches?
The question is critical because older technologies can be inaccurate, cause maintenance headaches, and exhibit poor reliability. Recent developments have solved many of the drawbacks common to older instruments.
Understanding what these new ideas are and how to apply them is the topic of my article in the February 2020 issue of Chemical Engineering, Taking Advantage of Improvements in Level Measurement Technology. It looks at two common approaches, differential pressure (DP), and radar, and how they have gotten better in recent years.
Starting with DP, we know it works when applied well, but many users still struggle with some of its longstanding problems related to specific application issues:
Using DP to measure fluid levels is not without its challenges. Most problems relate to the necessity of mounting the head space pressure tap some distance above the tank bottom, and then connecting it to a DP transmitter using impulse lines. Since those impulse lines are connected directly to the process, they are often a source of headaches for any kind of DP application, because they can plug from accumulated debris, fill with the wrong product (gas in liquid lines and vice versa), and are subject to freezing and other environmental effects.
One of the biggest advances for DP level is getting rid of impulse lines by using Emerson’s Rosemount 3051S Electronic Remote Sensor (ERS) System. It is engineered with a flexible, digital architecture to calculate differential pressure electronically using two pressure sensors linked together with an electrical cable. This improves accuracy and gets rid of the impulse line headaches.
Radar has also made some advancements, including an improvement on traditional pulsed non-contact transmitters in the form of frequency modulated continuous wave.
With FMCW, the transmitter sends a continuous signal sweep with a constantly changing frequency. The frequency of the reflected signal is compared with the frequency of the signal transmitted at that moment, and the difference between these frequencies is proportional to the distance from the radar to the surface, providing the level measurement. Until recently, pulse radar transmitters were the only units suitable for two-wire installations, due to the higher power consumption of FMCW, but advances in FMCW transmitter electronics have solved this problem. This is a major advance for many users because the FMCW transmitters actually provide much stronger signals due to the amount of information allowed by the stream of signals, as opposed to single pulses.
The prime example of this advance is Emerson’s Rosemount 5408 Level Transmitter which delivers accurate, reliable measurements on both liquids and solids. Using two-wire FMCW technology, the Rosemount 5408 deploys a continuous echo to maximize radar signal strength and produce a more robust and reliable measurement. It is even available with a SIL 2 rating for safety-related applications.
So, think about the level measuring instruments are in your plant:
Are you happy with the answers to those questions? Tell us about the problems you’re dealing with on a daily basis and your creative solutions. You can share with others about your implementations and experiences at the Emerson Exchange 365 community forum, a place where you can exchange ideas and experiences with others in the same situation. It’s a site where you can communicate with experts and peers in all sorts of industries around the world. Look for the Level Community, plus other specialty areas for opportunities to provide input, suggestions, and answers.