Showing posts with label continuous level. Show all posts
Showing posts with label continuous level. Show all posts

Monday, December 14, 2015

Process Measurement - Tank Fluid Level Measurement

industrial magnetic level indicator
Industrial Magnetic Tank Level Indicator
Courtesy Granzow
Industrial process control often requires the storage of liquid in vessels or tanks. Continuous and accurate indication of the liquid level within the tank is an essential data point for safety and process control. There are a number of methods and instrument types utilized to provide tank level measurement, each with attributes that may be advantageous for a particular installation. Some of the selection criteria for a tank fluid level indicator may include:
  • Direct or indirect measurement of level
  • Tank shape, regular or irregular
  • Media compatibility with measurement device
  • Requirements for maintenance or calibration
  • Compatibility with process temperature and pressure range
  • Local display and visibility
  • Level indication signal type and transmission
  • Level alarm switches or other indicators
When the instrument of choice is a magnetic level indicator, also referred to as a magnetic level gauge, the selection has usually hinged upon one of this instrument's strengths. Its use for providing level indication has a number of positive attributes:
  • Continuous level measurement
  • Operable without electric power
  • Direct visual tank fluid level indication, regardless of tank shape or profile.
  • Wide range of operating temperature and pressure
  • Breakage resistant construction
  • Range of construction materials available to accommodate corrosive media
  • Measuring indicators, switches, and transmitters mounted externally, without contacting the medium being measured.
  • Low maintenance operation.
  • Readable level indication from greater distance than glass sight gauges.
  • Applicable to large fluid level ranges with a single instrument.
These process measurement devices have a strong position in the tank level measurement field and should be considered as a candidate for fulfilling those application requirements. I have included a technical data sheet from Granzow, one of several manufacturers of this type of instrument, so you can see more detail. Share your application challenges with a sales engineer that specializes in level measurement. Combining your process knowledge with their product application expertise will yield positive solutions.

Thursday, July 16, 2015

Downpipe Liquid Level Sensor Purge Control

Downpipe bubbler type tank level indicator
Arrangement for bubbler type tank level indicator
with purge control
Courtesy King Gage
Industrial process control often requires the measurement of liquid inventory volume or mass. If the material is contained within a tank of known shape and dimensions, the volume can be determined accurately by measuring the level of the liquid. Various means are used to determine the liquid level. One of the simplest is the downpipe sensor, sometimes referred to as a "bubbler", where liquid level is inferentially derived using differential pressure. The downpipe is a length of pipe that is open at the end extending down into the liquid contained within the tank. The top end is connected to a purging device that provides a controlled flow of pressurized air or gas into the pipe. The pressure maintained within the downpipe will reach an equilibrium with the pressure produced by the hydrostatic force related to liquid level in the tank or vessel. Accurate measurement of this pressure, along with a thorough knowledge of the liquid's properties, can be used to determine the depth of the liquid within the tank and the corresponding volume.

King-Gage manufactures several industrial process level measurement devices incorporating downpipe purge technology and differential pressure measurement. They have applications in inventory monitoring, process control, hazardous and explosion zones, ballast monitoring, and other areas that benefit from their simple operation, low maintenance, and ruggedness. The company, in its own words describes the unit as an...
...extremely rugged unit designed specifically for hazardous areas requiring flameproof or ATEX (Ex d) rating. A proprietary wet check assembly ensures positive seal of fluids to ensure containment integrity. Loop powered transmitter provides 4-20mAdc output while components are isolated from the process media by a continuous air purge. Total consumption rate is less than 0.083 scfm for energy saving operation with external air/gas supply.The only internal element is a simple length of pipe extending into the tank.
Rugged design requires no setup or air flow adjustment due to its differential pressure regulation that avoids dynamic pressure drops common to other bubblers. This ensures highly accurate level measurement and repeatability within ± 0.2% while preventing turbulence or foaming of tank liquid. Applications include water/wastewater, sulfur pits, most free flowing liquids (including slurries) and temperatures in excess of 160 °C (320 °F) as the transmitter is effectively isolated from the process by the air purge.
The slides below illustrate various installation configurations, including one for explosion hazard areas. Contact an application engineer for more detailed information.

Wednesday, November 12, 2014

Guided-wave Radar Level Sensing

Time domain reflectometry for guided-wave radar level
 Guided-wave Radar Level Sensing based
upon Time domain reflectometry (TDR)
(image courtesy of Wikipedia)
Guided-wave radar (GWR) uses a probe immersed in the process media to guide high-frequency electromagnetic waves into the media being measured, and then analyzes the reflected energy to determine level.

GWR is based upon the phenomena of time domain reflectometry (TDR). TDR begins with the initiation of a low-energy electromagnetic pulse of energy into a process through a probe. The subsequent measurement of the energy reflected from the surface of the medium being measured is communicated from the probe to the instrument electronics. By analyzing the reflected waveform, a calculation of level can be made. The instrument then correlates the waveform information to a continuous, or switched, output signal.

Guided-wave radar level transmitter
Guided-wave radar
level transmitter
(courtesy of King Gage)
Guided-wave radar isn’t dependent or subject to the process media properties it is sensing, unlike other electronic level sensing technologies, and can be used for both liquids and solids.

GWR is best suited for the following types of applications:

  • Processes undergoing turbulence or changing density or viscosity.
  • Moving, agitated, foaming, vaporous or circulating surfaces.
  • Processes with higher temperatures and pressures.
  • Sticky or gummy processes, such as oil, paint, rubber or tar.
  • Fine particulate processes such as carbon black, salt, or grain.

One significant advantage to guided-wave radar is that build up on the probe has no effect on the accuracy. While this might be counter-intuitive, the GWR technology “ignores” the relatively insignificant amount of probe build up. This is because the signal returned from the electromagnetic pulse corresponding from the actual process media level is always larger than any reflected signal from build up, which makes it easy for the instrument to determine the difference.

For more information on guided-wave radar level controls, contact:

Mountain States Engineering and Controls
1520 Iris Street
Lakewood, CO 80215
303.232.4100 Phone
303.232.4900 Fax

Wednesday, August 20, 2014

Level Measurement

level measurement
Level Indicator
Level measurement is an important process measurement. In many processes, it is important to measure the level of various liquid and solid materials. Effective level measurement provides reliable and continuous operations by maintaining optimum material inventory, by maximizing plant availability, and the prevention of spillages and other process disturbances.

Level is measured at the interface between two material "phases", that is, between liquid and air or solid and air, or other different density materials. The different phases must be clearly separated. When liquids are thoroughly mixed together, level cannot be measured because there is no separation of phases. The interface must be definite in nature.

In the case of an open tank filled with water, the point at which water and air contact is the definite interface, or phase change. Another interface example would be between oil and water. In this example, the specific gravity of oil is less than water, so oil floats on top, but in separate form. Liquids that mix well together do not have a clear interface, so it is difficult to determine level of each.