Wednesday, September 30, 2015

Ultrasonic Level Measurement


Ultrasonic level instruments measure the distance from the transmitter (located at some high point) to the surface of a process material located farther below using reflected sound waves. The frequency of these waves extend beyond the range of human hearing, which is why they are called ultrasonic. The time-of-flight for a sound pulse indicates this distance, and is interpreted by the transmitter electronics as process level. These transmitters may output a signal corresponding either to the fullness of the vessel (fillage) or the amount of empty space remaining at the top of a vessel (ullage).

Ullage is the “natural” mode of measurement for this sort of level instrument, because the sound wave’s time-of-flight is a direct function of how much empty space exists between the liquid surface and the top of the vessel. Total tank height will always be the sum of fillage and ullage, though. If the ultrasonic level transmitter is programmed with the vessel’s total height, it may calculate fillage via simple subtraction:

Fillage = Total height − Ullage

If a sound wave encounters a sudden change in material density, some of that wave’s energy will be reflected in the form of another wave in the opposite direction. In other words, the sound wave will “echo” when it reaches a discontinuity in density20. This is the basis of all ultrasonic ranging devices. Thus, in order for an ultrasonic level transmitter to function reliably, the difference in densities at the interface between liquid and gas must be large. Distinct interfaces of liquid and gas almost always exhibit huge differences in density, and so are relatively easy to detect using ultrasonic waves. Liquids with a heavy layer of foam floating on top are more difficult, since the foam is less dense than the liquid, but considerably denser than the gas above.

A weak echo will be generated at the interface of foam and gas, and another generated at the interface of liquid and foam, with the foam acting to scatter and dissipate much of the second echo’s energy.

The instrument itself consists of an electronics module containing all the power, computation, and signal processing circuits; plus an ultrasonic transducer to send and receive the sound waves. This transducer is typically piezoelectric in nature, being the equivalent of a very high-frequency audio speaker.

The ISA-standard designations for each component would be “LT” (level transmitter) for the electronics module and “LE” (level element) for the transducer, respectively. Even though we call the device responsible for transmitting and receiving the sound waves a transducer (in the scientific sense of the word), its function as a process instrument is to be the primary sensing element for the level measurement system, and therefore it is more properly designated a “level element” (LE).

This photograph shows a typical installation for an ultrasonic level-sensing element (LE), here sensing the level of wastewater in an open channel:


If the ultrasonic transducer is rugged enough, and the process vessel sufficiently free of sludge and other sound-damping materials accumulating at the vessel bottom, the transducer may be mounted at the bottom of the vessel, bouncing sound waves off the liquid surface through the liquid itself rather than through the vapor space. As stated previously, any significant difference in material densities is sufficient to reflect a sound wave. This being the case, it shouldn’t matter which material the incident sound wave propagates through first:

This arrangement makes fillage the natural measurement, and ullage a derived measurement (calculated by subtraction from total vessel height).

Ullage = Total height − Fillage

As mentioned previously, the calibration of an ultrasonic level transmitter depends on the speed of sound through the medium between the transducer and the interface. For top-mounted transducers, this is the speed of sound through the air (or vapor) over the liquid, since this is the medium through which the incident and reflected wave travel time is measured. For bottom-mounted transducers, this is the speed of sound through the liquid. In either case, to ensure good accuracy, one must make sure the speed of sound through the “timed” travel path remains reasonably constant (or else compensate for changes in the speed of sound through that medium by use of temperature or pressure measurements and a compensating algorithm).

For more information, check out this online document or visit Ives Equipment at www.ivesequipment.com.


(Attribution to Tony R. Kuphaldt under Creative Commons Attribution 3.0 United States License)

Wednesday, September 23, 2015

Introduction to Electrically Actuated Valves (Motor Operated Valve or MOVs)

electric valve actuators
Electric valve actuators for MOVs
The two most common methods of opening and closing industrial valves are by pneumatic actuators and electric actuators. This video introduces the viewer to electric valve operation.

Commonly known as "motor operated valves", or MOVs, electric operators can be fitted to any quarter-turn valve (90 deg. rotation) (such as a ball, butterfly or plug valve), or linear movement valve (such as a globe or gate valve).

Most often electric actuators are used where electric power is readily available and a pneumatic air systems are not. They are available in a variety of voltages and torque outputs for various size valves. Accessories such as limit switches, positioners, and hazardous area enclosures are available as well.

Thursday, September 17, 2015

Simplifying Plant Safety instrumentation

White paper courtesy of United Electric Controls

Safety implementation typically is done by a group that includes plant instrument engineers and technicians, who are charged with finding simple and reliable solutions. Often, these situations involve the question of when to shut a process down. Such decisions frequently hinge on key process variables such as flow, level, temperature and pressure. these must be in a specified range at various locations within chemical and petrochemical plants, refineries and power plants, including everything from critical process vessels to eye wash stations.

For such point safety applications, a properly designed and implemented digital switch with self-diagnostics can be an important part of the answer. As an element of a multiple technology solution, a digital switch-based approach can help eliminate common-mode failures, significantly improve response time, achieve needed safety integrity levels (SILs), and simplify plant safety instrumentation.

To read the entire white paper, see the embedded document below:

Tuesday, September 8, 2015

Electronically Enhanced Solenoid Valves - Voltage Ranging Valves

Voltage Ranging Valves
Electronically Enhanced
Solenoid Valves
Voltage Ranging Valves
(courtesy of ASCO)
New power management technology is rewriting industry standards for reliability and power consumption of solenoid valve coils. The new technology solenoid valves accepts both AC and DC voltages while improving performance. Available in 2-way, 3-way and 4-way, these solenoid valves are designed to handle most fluid control applications.

The enhanced valves are designed to be drop in replacements for existing valves. There is no change to functional attributes such as flow, pressure, ambient & fluid temperatures or physical attributes such as envelope size and face-to-face dimensions. If you're looking to just switch out a coil,  enhanced coil kits are direct replacements for the old coil kits.

Here are the benefits to end customers:

Lower Power Consumption
  • 1.0 watt (DC version) & 1.5 watts (AC/DC versions)
  • Lowers energy cost up to 80% compared to standard solenoid valves 
RoHS 2 Compliant
  • Satisfies CE Directives 2002/95/EC and 2001/65/EU (RoHS 2) for the restriction of hazardous substances 
Supervisory Current Compatible
  • Suitable for systems employing supervisory currents not exceeding the following drop-out currents:
    • 20mA (12-24V DC), 15mA (24-120V AC/DC) and 7mA (100-240V AC/DC) 
  • Also suitable with devices having leakage currents not exceeding the drop-out currents noted above. 
Broad Voltage Ranges Reduce Inventory
  • Available in 24-120V AC/DC, 100-240V AC/DC & 12-24V DC 
  • Covers hundreds of global voltage requirements
  • Simplifies product selection and reduces complexity
  • Lowers inventory cost by eliminating need to stock both AC & DC products
  • Includes 125VDC battery (AC/DC versions) & 24VDC battery (DC version) 
DC Performance Increased Up to 500% To Match AC Ratings 
  • Transition from AC to DC without sacrificing performance
  • Eliminates the need for separate AC & DC output cards
  • Simplifies control schemes 
Integrated Surge Suppression
  • Prolongs the life of the coil by suppressing external voltage spikes
  • Lowers system cost by eliminating the need for additional surge protection 
Fit For Use In Rugged and Demanding Environments
  • Wide ambient temperature range for hot and cold environments
  • Enclosure Types 1 through 4X for indoor and outdoor applications o Optional Class 1, Division 2 coils available for hazardous locations 
No AC Hum
  • Ideal for applications requiring quiet operation

Tuesday, September 1, 2015

High-Temperature Capable Flammability Analyzer Increases Profit at Plastics Product Manufacturer

flammability analyzer
Flammability analyzer designed for
tough industrial applications
(courtesy of Control Instruments Corporation)
The customer is global supplier of vibration damping and sealing products for the automotive, consumer electronic and industrial markets that sells elastomer-coated metals, gaskets, brake shims and automotive and brake noise insulators. They also manufacture a variety of sealing materials, such as deck plates, oil filter adaptors, water outlets, pumps, relief valves, and rear cam and surge tank covers.

In their process solvents are applied to a web material. The web material contains PTFE and/ or rubber based adhesives and at times silicone. The main solvent component used is MEK which is not a high flash point solvent. Flammability analyzers were being used to monitor the flammability levels of the varying solvent levels in the zone’s atmosphere.

The flammability analyzers were mounted fairly far from the oven because of operating temperatures, and subsequently had long sampling lines. The last three zones were very challenging due to the distance and the use PTFE, silicones and other resins. Because the lines were so long, they were clogging from VOCs and vaporized web material and required the line to be shut down and cleaned. The downtime meant loss of production and loss of profits. The customer tried adding end-of-line filters on all sample tubing, which helped, but didn't solve the problem.

To solve the problem, the customer upgraded to a new flammability analyzer (a CIC model SNR674) rated for operating temperatures high enough (392 F) to keep all the elements in a vapor state and designed for use in a dirty environment. Theses new flammability analyzers are mounted directly on the oven wall eliminating the long sample lines. By keeping the sample lines as short as possible they were able to minimize the VOC condensation and eliminate the clogging.

For more information, contact:

Ives Equipment
(877) 768-1600
www.ivesequipment.com