What Advantages Do Displacer Transmitters Have Over Differential Pressure Level Transmitters?

Displacer
Transmitter
(Magnetrol)

Many technologies have been available over the years have helped the process control industry with level measurement. From basic mechanical float-operated level switches, the process automation industry has been developing new technologies to make industry safer and more efficient.

An example of a "tried and true" technology that was commonly used in the process automation industry is the DP (differential pressure) level transmitter. First introduced in the 1950s, DP transmitters measures the hydrostatic (head) pressure of a liquid in a tank or vessel and interprets this as level, based on the density/specific gravity of the liquid and programmed in by the user. A newer, alternative technology to DP transmitters is the displacer level transmitter, a device also based on specific gravity. While they both are dependent on specific gravity, they are significantly different in areas of installation, accuracy, and maintenance requirement.

Application/Calibration

Applying a DP transmitter or displacer level transmitter requires experience and there are many factors to be considered. Here are a few:

DP transmitters use inferential measurement to determine level measurement from the hydrostatic pressure.  Despite requiring the specific gravity variable having to be programmed into the transmitter electronics, the level displacer transmitter is in contact with the process media and the level measurement is direct.

DP transmitters requires time consuming and expensive calibration/re-calibration if any of the set-up parameters change or if the same DP transmitter is used on different materials in the same tank.
Displacer transmitters only require two variables to be programmed (temperature and specific gravity), making it easier when running multiple products in the same tank.

Many displacer transmitters do not require liquid to be present for calibration. They are programmed (wet or dry) using software. A huge time and money saving over DP transmitters.

Mounting

The physical mounting of DP transmitters is limited, which can in some situations can become downright problematic. DP transmitters require (2) side-mounted entry locations on the vessel or tank, with one having to be near the bottom. As a general rule, the fewer the entry points of a tank or vessel, the better, because of leakage. Tank bottom entries all the more so.

Displacer transmitters are mounted to meet the requirements of the application and do not require a connection at the bottom of the tank.

Installation Cost

While DP transmitters have a lower unit cost, adding ancillary components such as tubing and heat tracing can quickly "level" the installation cost playing field. Furthermore, don't discount the time cost savings when setting up, calibrating and re-calibrating displacer transmitters.

Temperature Range

DP transmitters have a normal operating temperature of up to 250°F, with an upper limit of 650°F when special options are specified.

Displacer transmitter can be used up to 850°F, very helpful particularly with level measurement in a hot oil separator application.

There are many options and variants to accommodate industrial level applications. Share your level application challenges with instrumentation specialists, leveraging your own knowledge and experience with their product application expertise to develop the most effective solution.

Cashco / Valve Concepts Model 3100 Packing Material Removal and Weight Installation Instructions

Valve Concepts Model 3100

The Model 3100 end-of-line conservation breather vent is part of the Valve Concepts, Inc. modular vent product line. The Model 3100 can easily be field converted to a vacuum only vent, a pressure/vacuum vent with pipe away and can either be direct acting or pilot operated.

The Model 3100 end-of-line conservation breather vent is designed for use on atmospheric and low-pressure storage tanks where pressure and vacuum relief is required.

How it Works

Weight loaded pallets in the vent housing allow the intake of air and the escape of vapors as the tank breathes due to thermal changes and product movement in and out of the tank. The pallets open and close to permit in breathing and out breathing necessary to maintain the tank pressure within permissible limits to avoid damage to the tank.

Paperless + Wireless Process Control Recorder

Paperless and Wireless
Yokogawa GX20W

There are probably few among us who long for the days when process recorders used paper. Video based graphic (also known as paperless) recorders, aside from being paperless, provide a broad range of functionality that empowers a user to display and deliver process information in whatever way is most useful for the application.

High sampling speed of multiple inputs that can be configured to accommodate a range of input signals, along with data storage, network communications and programmable alarm outputs power up the usefulness of these instruments for monitoring and documenting process operation. Many utilize touch sensitive screens, eliminating any buttons or keys on the operator panel.

Some of the great features available on today's paperless recorders:

• Multiple channels of input
• Start/stop recording by batch, and create data files
• Ample internal memory
• Creation of template-based Excel spreadsheets
• Custom display function
• Historical data with date and time calendar search function
• Ethernet interface
• PROFIBUS-DP and EtherNet/IP protocols
• Dust and splash-proof front panel
• Front panel door lock and login function

Wireless Seals the Deal

Wireless technology is a serious contributor in the effort to improve plant efficiency, lower risk, and increase productivity. Wireless recorders are now available for monitoring virtual all process variables such as pressure, temperature, level, and flow (plus many more).  The use of wireless recorders provides a compelling argument when you consider installation cost savings and convenience.  Savings estimates as high as 70% are realized when compared to the cost using cables for the same application.

There are many options and variants to accommodate every conceivable process control application. Share your data acquisition and process monitoring challenges with instrumentation specialists, leveraging your own knowledge and experience with their product application expertise to develop an effective solution.

For more information on paperless recorders, contact Miller Energy by visiting https://millerenergy.com or calling 908-755-6700 in NJ or 610-363-6200 in PA.