Level Sensors for Corrosive Liquids

Levelpro plastic level sensors
ICON Levelpro plastic level sensors.
Corrosive liquids can be found in just about every industry; food, metal finishing, water-waste water treatment, textile, automotive, to name just a few.  When it comes to selecting the correct sensor technology there are many different factors to consider.

Plastic level sensors are an excellent choice for corrosive liquid chemical applications.  Plastics, unlike metals, do not corrode; however, they can deteriorate and swell if the correct plastic is not used.

ICON Process Controls offers its Levelpro plastic level sensors for continuous level indication, as well as plastic level switches for point level notification.  There are many different factors to consider when selecting the right product for the application.

  • Chemical Liquid?
  • Concentration?
  • Temperature?

With this information a material of construction for the level sensor can be selected.  Next, it is important to understand other factors that contribute to the success or failure of the level sensor.

  • Is there particulate with the liquid?
  • Does the liquid create a film, or does it have a coating effect?
  • Does the chemical produce foam?
  • Is there sludge at the bottom of the tank?
  • Is the liquid agitated?

Once the information pertaining to the chemical and the type of sensor technology (continuous or point) is determined, ICON can recommend the most suitable product for the application.

An excellent level sensor for corrosive liquids is the 100 Series submersible level sensor.  The plastic level transmitter is available in PVC, PP and PVDF bodies, and comes standard with a corrosion-resistant PTFE jacketed cable and Kalrez O-rings.  The 100 Series submersible level sensors incorporate a weighted body which ensures the sensor sits at the bottom of the tank.  The plastic level transmitter has a ceramic sensing diaphragm that measures the head pressure of the liquid.  These level sensors are not affected by foam, vapor, condensate or turbulence, making them an excellent choice for many different applications.

If the chemical produces sludge then ICON would recommend a non-contact level technology such as the Ultrapro ultrasonic level sensor, or the Proscan radar transmitter.

For clean liquids the CFL Series continuous float is a reliable and economical choice.

ICON also offers a complete line of plastic level switches for point level indication.  These plastic switches are available in PVC, PP and PVDF materials, and the relay can be set to normally open or normally closed positions. Visit M.S. Jacobs at https://msjacobs.com for more information.

WIKA Phases Out PSD-30 and PSD-31 Pressure Switches, Replaced with PSD-4 Pressure Switch

PSD-4 Pressure Switch
The WIKA PSD-30 and PSD-31 pressure switches are currently being phased out, to be replaced with the newly updated PSD-4 pressure switch.

The model PSD-4 pressure switch represents the extensive development of the  PSD-30 pressure switch.  A high accuracy of 0.5 %, freely configurable output signals (PNP/NPN, 4-20 mA / 0-10 V), the 5:1 scalability of the analog output, in addition to outstanding self-diagnostics, make the PSD-4 an excellent automation solution for industrial machines, hydraulic systems, and pneumatic systems applications.

While the PSD-4 offers new features and functionality, pricing is comparable to that of the PSD-30 and PSD-31.  This new pressure transmitter offers customizable features, such as allowing the user to select the switch type and output signal, while offering a 5:1 turndown ratio.  Additionally, this transmitter is an economical solution for applications requiring local display with an analog output signal.  The PSD-4 provides an upgrade in quality and customizability without negatively affecting budgets.

During development of the WIKA switch family a high value was placed on a robust design and the selection of appropriate materials suited to machine-building applications.  For this reason the case and the threaded connection of the electrical connector are made from stainless steel.

For more information, contact M.S. Jacobs by visiting https://msjacobs.com or by calling 800-348-0089.

M.S. Jacobs: Dedicated to Service and Excellence in Process Control

M.S. Jacobs and Associates has been a leading manufacturer's representative and distributor of industrial instrumentation and controls since 1945.  Expanding from its original focus on the steel industry, MS Jacobs services and supplies products in all major industrial markets, including power generation, chemical processing, pulp and paper, oil and gas production, water and wastewater treatment, nuclear power, pharmaceutical, institutional, and alternative energy.

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For more information, contact M.S. Jacobs by visiting https://msjacobs.com or calling 800-348-0089.


Why Choose Displacer Level Transmitters Over Differential Pressure Level Transmitters?

DP level transmitter diagram
DP level transmitter diagram.
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 Considerations
Displacer transmitter
Displacer transmitter
construction.
  • Infers Level vs. Direct Contact - 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.
  • Time Required to Set up / Calibrate: 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. Furthermore, 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 Considerations
  • Orientation and Tank Penetration - 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 are all the more so concerning. Displacer transmitters are mounted to meet the requirements of the application and do not require a connection at the bottom of the tank.

Displacer transmitter
Displacer transmitter.
(Magnetrol)
Installation Cost
  • Consider Overall Installed 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 Considerations
  • 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.