Level Measurement Solutions for Water Treatment

Several functional level measurement technologies have viable solutions for a broad range of industrial and municipal water treatment applications. Because of the variety of applications that exist and the varying application conditions, no one technology is best suited in all cases. 

POINT LEVEL VERSUS CONTINUOUS LEVEL INSTRUMENTS

Regardless of the application, there are two significant classifications of level measurement instrumentation: point level and continuous level measurement.

Point Level (On/Off) measurement indicates the absence or presence of level at a certain threshold (point) within a vessel.  Point-level switches perform as high level and spill prevention alarms, low level, pump protection alarms and pump control.

Continuous Level (Proportional) measurement indicates the level in a vessel over the full span of capacity.  These devices perform as process control as well as inventory control and management.

LEVEL CONTROL TECHNOLOGY CHOICES

The technologies used to measure level are affected differently by the varying process conditions. Below is a brief description of the different technologies commonly used in a water treatment facility.

RF ADMITTANCE/CAPACITANCE
RF Admittance/Capacitance employs a radio frequency signal and monitors for a change in capacitance. Either the presence or absence of material or how much material is in contact with the sensor, making it highly versatile and a right choice for a wide range of conditions and materials for point or continuous level measurement.

RADAR
Radar utilizes either Pulsed Wave or Frequency Modulated Continuous Wave (FMCW) through-air transmission that allows for an accurate non-contact reading of reflected electromagnetic signals.

MAGNETOSTRICTIVE
Magnetostrictive uses an electric pulse from ferromagnetic wire to accurately detect a float's position with embedded magnets.  As the pulse intersects the float's magnetic field, a second pulse reflects an electric circuit that accurately determines the distance and thus the level position.

CONDUCTIVITY SWITCHES
Conductivity switches measure the drop-in resistance when a conductive liquid contacts with two probes or a probe and a vessel wall.

ULTRASONIC (POINT LEVEL)
Ultrasonic (Point Level) measurement electronically resonates a crystal at a fixed frequency to generate sound waves that travel across an air gap to a second crystal.  As liquid fills the gap between the two crystals, the second crystal begins to resonate with the first.

ULTRASONIC (CONTINUOUS LEVEL)
Ultrasonic (Continuous Level) measurement uses a transmitter to generate an ultrasonic pulse and measures the time it takes for a reflected signal to return to the transducer to determine a liquid level.

GUIDED WAVE RADAR (GWR)
Guided Wave Radar (GWR) utilizes a Time Domain Reflectometry (TDR) technique by sending a highly focused electronic signal down a metallic rod or flexible cable waveguide. When the transmitted signal intersects the liquid's surface, it reflects along the rod or cable to determine the distance traveled. The level position is then easily inferred.

HYDROSTATIC
Hydrostatic measurement immerses a pressure transmitter with a sensing diaphragm and a sealed electronic circuitry that transmits an analog signal proportional to the liquid level above the sensor.

FLOAT SWITCHES
Float switches rely on a low-density float mounted in a vessel that magnetically couples to a limit switch. A change in fluid height actuates a switch by moving the float.

VIBRATION/TUNING FORK
The Vibration/Tuning fork is piezoelectrically energized and vibrates at a frequency of approximately 1200Hz, and as the process media cover the fork, the frequency shifts. The internal oscillator the frequency shift by and converts it into a switching command.

POINT LEVEL SOLUTIONS

Advanced RF Admittance/Capacitance point level devices are the most versatile of the point level technologies, especially with process media that can coat the sensor. They provide excellent spill/overfill protection. They are simple to install and have no moving parts, making them virtually maintenance-free. Their robust design and circuitry make them an ideal solution for many water treatment applications.

Both tuning forks and ultrasonic gap switches provide reliable high- or low-level measurements in various applications. For non-coating conductive liquids, conductivity switches provide economic priced measurement while float switches appear in many basic applications at very cost-effective prices.

CONTINUOUS LEVEL SOLUTIONS

Mechanical systems such as floats and bubblers require extensive maintenance and are less reliable and accurate than electronic systems. Hydrostatic systems afford better reliability and are simple to use, and can transmit data to another receiver for remote monitoring, recording, and control.

RF Admittance/Capacitance level is a time-proven and one of the best available technologies for indication and control. RF technology inherently provides the highest accuracy and repeatability in interface measurements. Variations in the makeup of upper and lower phases of a liquid have no appreciable effect on system accuracy. Recalibration is not required.

For short-span measurements, RF Admittance technology provides one of the most preferred readings. As the level of measurement span decreases, the more appropriate RF technology becomes. In spans of only a few inches, RF systems can repeatedly produce accuracies of 1/32ths of an inch. RF has the added benefit of not being limited by “dead zones” inherent with many popular technologies often selected for measurement ranges larger than 5 feet.

Non-metallic tanks pose no technical problems for Ultrasonic, Magnetostrictive, Hydrostatic Pressure, Radar, and GWR (Guided Wave Radar) technologies. The GWR approach is suitable for vessels with internal obstructions and uses lower energy levels than airborne radar technologies. Non-contact technologies, such as Radar and Ultrasonic, can have measurement ranges up to 130 feet. 

For long-range measurements or headroom limitations, flexible sensors offer insertion lengths up to several hundred feet for Hydrostatic Pressure and RF Admittance technology products. Loop-powered GWR (TDR)-based products allow measurement ranges up to 115 feet in selected applications. Magnetostrictive technology provides an accuracy of 0.1% of measurement span in flexible sensor designs up to a maximum range of 70 feet.

Piping Specialties / PSI Controls

https://psi-team.com

800-223-1468

Level Measurement for Water in Sewage Pools

This application takes place at a large power plant well known for its "Green Approach" and it's commitment to ensuring a clean and healthy atmosphere in and around the plant. 

The branched sewer system of the power plant requires instant maintenance and control. The plant uses water to operate the turbine. This water and other wastes move to the city’s wastewater treatment plant through the sewage system.

Some of the sewers are dispersed in remote locations around the plant, making it difficult for personal maintenance personnel to approach and repair damage on time. Plant technicians were looking for a solution to control the sewers better and avoid cases where wastewater might overflow. 

The sewage pool readings had to be transmitted to the central DCS because the sewage system connects to a central control room. The plant needed a 24/7 watch and an on-site guard to gain maximum control over those sewers. 

Technicians also stressed that wastewater flooding was inevitable because it takes time for the equipment to handle blockages. This flooding has caused severe damage to the environment. It was essential to control the wastewater level in the sewers to avoid cases such as these from reappearing. 

The Drexelbrook Usonic - The Solution 

After a lengthy examination of several possibilities, the plant decided to install two Drexelbrook USonic systems in its sewage pools. The ability of USonic to produce non-contact, continuous, and accurate readings of the water level in the pools gave the engineers of the plant a clear picture of the pools' status. 

Its compact size and integral construction simplify its installation, offering an efficient solution in no time at all. The USonic had no problem providing 12ft water level readings with a measurement range of up to 30 ft.  It can map obstacles in the pool and memorize interfering signals with its scan distance function. 

The USonic was linked to the central control system via 4-20mA, allowing the plant engineers to control the water level in the sewers constantly. The engineers know that the sewers would maintain the correct water level, and the system would be alerted in an emergency. 

Summary

The two USonic systems installed in the power plant give complete control over the sewers' water level to the plant's engineers. The systems' ability to display continuous level readings around the clock improved maintenance crews handle the sewage system.

To detect sudden blockages and avoid environmental damage on time, they can now save time. The plant received an immediate return on investment due to its compact size and reduced price.

Piping Specialties / PSI Controls

https://psi-team.com

800-223-1468

Cost-effective, Non-contact Ultrasonic Level Measurement from Drexelbrook

Affordable, 2-Wire Level Transmitter with the performance and features of premium, line-powered systems.

DOWNLOAD THE USONIC DATA SHEET HERE

USonics ultrasonic technology level products from the Drexelbrook family offers a cost-effective two-wire and line powered versions for the non-contact measurement of liquids and slurries for level, distance, volume, and open channel flow.   Level, size, volume, and open-channel flow measurements are easily configured via a menu-driven display.   The USonic level transmitter has a 4-20 mA two-wire HART output signal and is suitable for all Class I Div. 1, Zone, I.S., or explosion-proof locations.

For more information contact PSI Controls / Piping Specialties by calling 800-223-1468 or visit https://psi-team.com.

Radar Level Measurement: Comparison of 24 GHz and 80 GHz

Radar level transmitters are among the most accurate technology choices for process level and storage tank applications for continuous level measurement under demanding conditions.  These transmitters utilize Frequency Modulated Continuous Wave (FMCW) technology that offers superior signal processing capabilities and more reliable measurement than other techniques. The state-of-the-art signal processing capabilities of these transmitters, along with their frequency range, helps to ensure optimum application coverage.

24 GHz radar transmitters cover a broad range of applications, including liquids & solids. 

80 GHz radar transmitters are especially beneficial for level measurements in narrow tanks with internal obstructions due to their small beam angle.

This video, courtesy of AMETEK Drexelbrook, demonstrates many of the other differences between 24 GHz and 80 GHz models of radar level transmitters.

For more information on radar level transmitters in New England, contact PSI Controls (Piping Specialties, Inc.). Call them at 800-223-1468 or visit their website at https://psi-team.com.

Wiring the AMETEK Drexelbrook Universal IV RF Admittance/Capacitance Continuous Level Measurement System

The video above describes how to wire the Drexelbrook Universal IV  Continuous Level Measurement System.

The Universal IV level system is the most advanced RF continuous level measurement system available. It includes worldwide hazardous location approval and is immune to vapor, dust and foam interference as well as to tank obstructions such as nozzles, ladders, pipes and agitators. The Universal IV features standard display/keypad, auto-ranging capabilities, local or remote installation, as well as state of the art measurement technology providing unmatched stability and accuracy. It is ideal for a wide array of level applications in industries such as oil and gas refining, water and wastewater along with the pharmaceutical and biotech industries.

The Pro Model integrates the RF Admittance technology with the versatility of Cote-Shield technology.  The Cote-Shield technology is designed to ignore coatings on the probe and measurement span of 1" to 800'. 

The Lite Model is the entry level RF Capacitance measurement system without Cote-Shield capabilities, can be used in non-coating conductive liquids and insulated coating applications where Cote-Shield is not required and offers a level measurement range up to 20' typically.

Universal IV RF Continuous Level Measurement System Features

• Easy one-time calibration
• Low cost of ownership, no maintenance and no moving parts to wear out
• Immune to tank obstructions such as nozzles, ladders, pipes and agitators
• Available as intrinsically safe systems
• Output: 4-20 mAdc, HART. Compatible with HART.
• Supply voltage: 13-30 VDC, 2 wire loop powered

For more information on the AMETEK Drexelbrook Universal IV RF Admittance/Capacitance Continuous Level Measurement System visit this link - https://psi-team.com/drexelbrook-universal/ or call 800-223-1468.

FMCW (Frequency Modulated Continuous Wave) Open Air Radar Level Measurement

Non-contact level measurement using radar transmitters for the continuous, contactless level measurement of liquids, pastes, granulates, powders and other solids in a wide variety of industries.

OPERATING PRINCIPLE

• The radar principle used is FMCW (Frequency Modulated Continuous Wave). The FMCW radar emits a high frequency signal whose frequency increases linearly during the measurement phase (called the frequency sweep). 
• The signal is emitted via an antenna, reflected off the product surface and received with a time delay, t. 
• Time delay, t=2d/c, where d is the distance to the product surface and c is the speed of light in the gas above the product. 
• For further signal processing the difference Δf is calculated from the actual transmitted frequency and the received frequency. 
• The difference is directly proportional to the distance.
• A large frequency difference corresponds to a large distance and vice versa. 
• The frequency difference f is transformed via a Fast Fourier Transformation (FFT) into a frequency spectrum and then the distance is calculated from the spectrum.
• The level results from the difference between the tank height and the measured distance.

Learn more about this technology by downloading the Drexelbrook DR Series brochure from this PSI web page.

For additional information, call Piping Specialties, PSI Controls at 800-223-1468 or visit their web site at https://psi-team.com.

Setting Up and Calibrating the Drexelbrook MultiPoint II Level Switch

This video demonstrates how to calibrate and set the Drexelbrook MultiPoint II level switch.

The Drexelbrook Multipoint II level switch product offers three control points located anywhere along a single vertically inserted level sensing element. This level switch can be used to provide high level, high-high level, and low level control points. It also provides an adjustable differential feature for one of the control points for pump on/pump off control making it ideal for sump level control. It is designed to be intrinsically safe for Class I Groups A,B,C,D and Class II Groups E,F,G (Div. 1 and 2). The unit is mounted in FM approved explosion proof housing. The MultiPoint II has no moving parts and the need for maintenance is therefore eliminated. The Drexelbrook MultiPoint II is an economical solution for processes requiring multiple operating points.

For more information about level instrumentation, contact Piping Specialties, Inc. / PSI Controls by calling 800-223-1468 or visit their web site at https://psi-team.com.

Plugged Chute Detection for Granular Materials

Detecting plugs in granular material conveying chutes is difficult due to the heavy, abrasive materials and dusty, coating nature of the environment. Many technologies used to detect material movement in chutes have considerable downside. For instance, regulatory requirements and source disposal problems make nuclear gauges an unappealing choice, insertion type sensors are quickly damaged by falling material, microwave sensors require two mounting windows to operate, and vibrating chute walls can damage electrical components.

A better alternative is the Drexelbrook Intellipoint RF Admittance Plugged Chute Detector. Its design allows for the reliable detection of a plugged chute, reducing costly downtime and material spill over.

The Drexelbrook plugged chute detector, also known as a blocked chute switch, reliably detects the presence or absence of bulk solids material flowing through chutes in an economical way without sacrificing flow speed. If process material stops flowing due to a plugged condition, the flush mounted capacitance sensing element will alarm, allowing further action to occur (alerting an operator, shutting down a conveyor belt, etc.). The Cote shield circuitry ignores even heavy coatings, and the flush mounted sensing element does not interfere with material flow. There are no moving parts to wear or jam, and thus, it requires virtually no maintenance. In fact, the Intellipoint Mean Time To Failure (MTTF) is calculated to more than 110 years!

There are no regulatory requirements with the adoption of the Intellipoint, and system electronics can be mounted remotely to eliminate vibration concerns. Due to the rugged sensor design this point level switch is ideal for coal, wood chips, ores and powders. This point level switch automatically recognizes and ignores coatings to prevent false alarms and, as it is flush mounted through a chute wall, nothing protrudes into the chute to interfere with or obstruct material flow.

Choosing the Intellipoint provides reliable detection of plugged chutes that will keep your plant running smoothly and virtually eliminates spills occurring due to plugged conditions.

Key Features

• Curved and flat sensors are available
• DPDT relay dry contacts at 5A, 120VAC
• Less maintenance than other technologies; no moving parts to hang up or wear out
• Uses Drexelbrook PML series electronics
• Supply voltage: 19-250 VAC, 18-200 VDC, Auto-detecting without jumpers

For more information, contact Piping Specialties, Inc. by calling 800-223-1468 or by visiting https://psi-team.com.

Problems with Measuring Level of High Density Pulp Stock

Level Measurement in Pulp Stock has posed problems for a wide range of level measurement technologies. In most pulp mills this is the most challenging application on site.

The environment in the high-density pulp tank is very corrosive to most common metals and the clouds of dense steam vapors that rise from the stock and foaming surface of the level are a constant source of signal loss for many non-contact technologies.

Due to the size of the vessel and density of the stock, mechanical devices are typically short  lived.Stock coatings that form on all interior surfaces add additional mechanical stress and the pulp coating deposits can adversely affect accurate level measurement performance.

One of the challenges of a level measurement device is to control the level in the stock tank, thereby helping to control the average pulp density by controlling the speed of the pump.The response time of the level measurement system is critical in controlling the pump speed and reducing pump oscillations and surges that will eventually reduce the life of the pump.Too slow of a response from the level instrument will allow the level to rise above it ’s optimum density level and cause excessive loading and wear on the pump.

DOWNLOAD THE FULL APPLICATION NOTE HERE

Piping Specialties, Inc.
PSI Controls
https://psi-team.com
800-223-1468

Problems with Measuring Level of High Density Pulp Stock from Piping Specialties, Inc and PSI Controls

The Drexelbrook USonic Non-contact Level Transmitter

The Drexelbrook USonic level transmitter provides a level measurement utilizing a non-contact ultrasonic sensor. Measurements of level, distance, volume and open channel flow is easily configured through the menu driven display. The Usonic level transmitter is offered with a two wire 4-20 mA, Hart output signal and is suitable for all Class I Div. 1, Zone 0, I.S. or XP locations.

For more information contact PSI Controls / Piping Specialties by calling 800-223-1468 or visit https://psi-team.com.

Level and Pressure Instrumentation for Pulp & Paper Production

Pulp and paper applications create a notoriously harsh, high moisture and chemical-laden environment; coupled with extreme vibration in many of the processes. The following document outlines an array of level, pressure, and position applications and solutions for the pulp & paper industry.

Download a copy of the Measurement Solutions for the Pulp & Paper Industry here.


Piping Specialties, Inc / PSI Controls
800 223-1468
https://psi-team.com

Level and Pressure Instrumentation for Pulp & Paper Production from Piping Specialties, Inc and PSI Controls

Drexelbrook’s ThePoint™ Series Point Level Switch: Settings, Adjustments, and Changing Calibration Modes

The AMETEK Drexelbrook ThePoint™ Series uses No-Cal™ technology to detect the presence or absence of material without calibration or initiation via setpoint adjustments, push-buttons or magnets.

ThePoint™ level measurement switch features both Auto-Cal and manual calibration. The standard Auto-Calibration mode is applicable to most liquid and slurry point level measurements. If preferred, the manual calibration can be used and is recommended for some application. ThePoint electronic unit has auto and manual calibration modes built into the standard unit and can be accessed through the simple routine shown in the video below. The inclusion of these calibration modes allows the Drexelbrook RF Point Level Products application flexibility that is far greater than any other point level product on the market. ThePoint™ level switch can be used in Liquids, Solids, Slurries, and Interface applications.

To learn more specific instructions on the (8) calibration modes ThePoint™ has available, download the "Drexelbrook ThePoint Series Point Level Switch Installation and Operating Instructions" from this link.

Continuous and Point Level Control Selection Guide

Drexelbrook Continuous and Point Level Control Products

Based on experience from of thousands of inquiries about level measurement, most questions boil down to "What is the best level measurement instrument for my application? That depends on quite a few application considerations, such as:

• Will the measured media add coating to the probe?
• Can the probe have contact with the media?
• Are there explosion hazards?
• What is the physical type of application, well, tank, open channel or floating roof tank?

This document can help deliver the perfect continuous level transmitter or level switches for your application.

Download a PDF version of the Drexelbrook Continuous and Point Level Control Selection Guide here, or view the embedded document below.

https://psi-team.com
800-223-1468

Drexelbrook Continuous & Point Level Selection Guide from Piping Specialties, Inc and PSI Controls

Floating Roof Tank Spill Prevention

Floating Roof Tank Spill Prevention (Drexelbrook)

One of the most difficult and critical applications is measuring the high alarm or potential overfill condition on a floating roof tank containing liquid petroleum products such as crude oil or refined products such as fuel. It normally is comprised of a cylindrical steel tank equipped with an internal or external floating roof, that floats on the surface of the stored liquid. Floating roof tank systems are especially beneficial in eliminating the evaporative losses of the liquids. As opposed to a fixed roof tank there is no vapor space in the tank. This helps to reduce risk in highly explosive vapor environments. This is an extremely high cost of failure application, and one in which only the safest and most trusted products are accepted.

Drexelbrook's
Intellipoint

Safe operation of the tank farm relies on critical real time continuous level measurements of the liquids in the tank, as well as detecting when a high level condition exists. Products used in this application are typically required to meet the API 2350 Overfill Protection Standards, as well as SIL Safety Integrity Level performance standards to IEC 61508.

The challenges to reliably detect a high level condition on a floating roof tank are long sensor length requirements, and the variability of what is being measured. The floating roof may be dry in which case you need to detect the position of the physical metal roof. Or there may be a few inches of rain water or petroleum liquids on the roof. Measuring instruments need to determine very accurately, usually within a few millimeters, when the position of the floating roof has reached a high level alarm condition.

Drexelbrook's Intellipoint, with its unique floating roof probe, can accurately detect and alarm on the position of the floating roof or the presence of liquid under all these conditions. The safety Intellipoint is a SIL2 fully certified RF admittance point level switch with uncompromising reliability for the most demanding applications.  Drexelbrook has almost 60 years of RF admittance technology experience and is proud to offer this specialized product as the latest in its award-winning portfolio for the level market.

Product features include:

• Adjustable up to 15 feet, or 4.6 meters, to accurately control the alarm point. 
• A trip point accuracy of a few millimeters.
• Fully SIL2 certified to IEC61508. 
• Worldwide hazardous area approvals .
• Meets overfill protection standards API2350.
• A floating roof tank probe that is unique in the industry.

Understanding Guided Wave Radar Level Instruments

Guided Wave Radar (GWR)
level transmitter (Drexelbrook)

One of several technologies used for level measurement in process control is guided wave radar. A Guided Wave Radar (GWR) level transmitter combines time domain reflectometry (TDR), equivalent time sampling (ETS), and low power circuitry with a form factor that includes a wave guide extending into the contained media. TDR measures distance or level using pulses of electromagnetic energy. The pulse travels along the waveguide until it reaches the media surface and is reflected back to the unit. The speed of the pulse is known, so an accurate measure of the travel time for the signal can be processed into a distance measurement. Different media will produce a range of amplitude in the reflection, with a greater dielectric difference between air and target medium producing higher amplitude in the reflection. Industries, such as telephone, computer, and power transmission, have relied on TDR for years in order to detect and pinpoint breaks in wires or cables, making the technology more mature than it may appear by its limited timeline in level measurement applications.

ETS is used to measure the high speed, low power electromagnetic energy, and is typical when applying TDR to level measurement technology, where the signal travel distance and time are very short. The electromagnetic signals are captured by the ETS technology in nanoseconds, and are then reconstructed in the equivalent time of milliseconds. The radar scans the waveguide, collecting thousands of samples to be used in signal processing. Integrating both technologies into a single level transmitter yields an accurate and responsive instrument for process measurement.

GWR instrumentation is useful in the process control industry for its ability to measure levels in a quick, consistent way. GWR transmitters are contact radar level measurement tools, as opposed to pulsed non-contact radar transmitters that emit radar pulses through free air without a waveguide. Probes, inserted into the subject tank or vessel, serve as the waveguide for the pulsed signal. They guide the pulsed microwave vertically into the tank, providing a measure of immunity from disturbance by the tank and surrounding media. Guided wave radar technology differs from non-contact radar in a number of ways. The presence or absence of a probe is only one of them.

GWR level transmitters are used in process measurement applications throughout many industries, such as food and beverage. Tanks, pumps, and piping systems for both storage and transport can utilize GWR to continuously monitor levels. Other vessels, such as reduction, forming, mixing, heating, cooking, and cooling, can utilize GWR for similar reasons. Additionally, other stages of food and beverage manufacturing, such as centrifugation and decontamination, can be good fits for GWR technology. Guided wave radarís previous applicability in industries aside from liquid processing and implementation in a wide range of process settings show the flexibility and reliability of GWR technology.

Selecting the best level measurement technology for an application can be a challenge. Share your project requirements and concerns with a process instrumentation specialist, combining your own process knowledge and experience with their product application expertise to develop effective solutions.

Measurement Solutions for the Water and Wastewater Industries

Measurement Solutions for the Water and Wastewater Industries from Piping Specialties, Inc and PSI Controls

Understanding Hydrostatic Pressure

Hydrostatic level transmitter
(Drexelbrook)

Pressure measurement is an inferential way to determine the height of a column of liquid in a vessel in process control. The vertical height of the fluid is directly proportional to the pressure at the bottom of the column, meaning the amount of pressure at the bottom of the column, due to gravity, relies on a constant to indicate a measurement. Regardless of whether the vessel is shaped like a funnel, a tube, a rectangle, or a concave polygon, the relationship between the height of the column and the accumulated fluid pressure is constant. Weight density depends on the liquid being measured, but the same method is used to determine the pressure.

A common method for measuring hydrostatic pressure is a simple gauge. The gauge is installed at the bottom of a vessel containing a column of liquid and returns a measurement in force per unit area units, such as PSI. Gauges can also be calibrated to return measurement in units representing the height of liquid since the linear relationship between the liquid height and the pressure. The particular density of a liquid allows for a calculation of specific gravity, which expresses how dense the liquid is when compared to water. Calculating the level or depth of a column of milk in a food and beverage industry storage vessel requires the hydrostatic pressure and the density of the milk. With these values, along with some constants, the depth of the liquid can be calculated.

The liquid depth measurement can be combined with known dimensions of the holding vessel to calculate the volume of liquid in the container. One measurement is made and combined with a host of constants to determine liquid volume. The density of the liquid must be constant in order for this method to be effective. Density variation would render the hydrostatic pressure measurement unreliable, so the method is best applied to operations where the liquid density is known and constant.

Interestingly, changes in liquid density will have no effect on measurement of liquid mass as opposed to volume as long as the area of the vessel being used to store the liquid remains constant. If a liquid inside a vessel that’s partially full were to experience a temperature increase, resulting in an expansion of volume with correspondingly lower density, the transmitter will be able to still calculate the exact mass of the liquid since the increase in the physical amount of liquid is proportional to a decrease in the liquid’s density. The intersecting relationships between the process variables in hydrostatic pressure measurement demonstrate both the flexibility of process instrumentation and how consistently reliable measurements depend on a number of process related factors.

Visit PSI-Team.com for more information on pressure and level instrumentation.

Level Measurement Technologies Provide Accurate Level Control & Ignore Foams in Filler Bowl Applications

RF Admittance and Magnetostrictive technologies have a proven performance record in gravity feed flow control for the dispensing of liquids into bottles or containers.

In high speed bottling operations many different filling methods can be used depending on the nature of the product and type of container being filled. For many Food and Beverage, and Pharmaceutical applications the preferred filling method is by using level measurements to control the gravity ow of liquids into bottles or containers from the filler bowl. The level measurement method is very consistent with liquids and slurries to prevent over-filling or under-filling of a bottle or container by keeping a consistent product level in the filler bowl. 

Level filling is the oldest filling method and is still largely favored in specific markets. This is largely due to products being sold in translucent containers. The consumer expects to see that all containers are filled to the same precise level and will reject a container with a level lower than others on the shelf. 

In a gravity feed filler bowl, the natural head pressure of the liquid is used to ll each bottle. The liquid level in the filler bowl must be kept at a constant level so the pressure within the filler bowl remains constant. This permits each bottle or container to ll to the correct level in the same amount of time. 

The Problem: 

Hydrostatic pressure level measurement systems, which have been traditionally used for this application, are found to have errors in level measurements when changing from one process material to the next, which usually has a slightly different specific gravity. As the process fluid’s specific gravity is changed, this leads to either an over- ll or under- ll condition. 

The Solution: 

AMETEK-Drexelbrook provides sanitary 3A approved systems in both RF Admittance and Magnetostrictive technologies for use in filler bowl measurements that remain unaffected by changes in specific gravity, changes in temperature or changes in pressure or vacuum. Both technologies can provide the accuracies that are required for reliable performance in the face of light or heavy liquid viscosities, foaming conditions, and have the ability to ignore process coatings that may develop on the sanitary sensors. The sensors are of rugged construction and will not be affected by the shock or vibration of the bottling process. 

RF Admittance systems are supplied with a Triclover fitting with a rigid Teflon coated sensor the length of the measurement range. Accuracy is ±1% of measured span. Systems are agency approved as intrinsically safe for Class I, Div. 1 hazardous installations. RF Admittance has the ability to measure a wide range of process materials and ignore most foam and process build-up on the sensor. Systems are powered by a two-wire, 24Vdc power source. 

Magnetostrictive systems are supplied with a Triclover fitting and use a 240 grit finished 316SS rigid sensor and oat. Accuracy is 0.1% of measured span. Systems are agency approved as intrinsically safe for Class I, Div. 1 hazardous installations. Magnetostrictive systems can easily ignore foaming conditions as the oat will sink through the foam and rest on the liquid surface. Systems are powered by a two-wire, 24Vdc power source. 

AMETEK-Drexelbrook systems can provide analog 4-20 mA, HART, or Honeywell DE outputs. Sensor lengths can be as small as a few inches to over 10 ft. All systems are maintenance free and can be easily con gured without complex calibration. 

AMETEK-Drexelbrook has successfully supplied filler bowl level measurement systems to many major Food & Beverage and Pharmaceutical customers over the past 40 years and have hundreds of successful applications on products such as milk, fruit and vegetable juices, jellies, baby foods, soups, beer, spirits, ground meat, pet foods, sodas, and more.