Process Measurement and Control: When To Use a Diaphragm Seal

Diaphragm seal for pressure measurement device
Courtesy Wika

Process measurement sensors are not indestructible. Not even the most rugged device is fully immune to the chemical nature of process media or the kinetic impact associated with fluid composition and movement. Balancing degrees of protection, usually to increase the useful life of the device, with sensor response and accuracy is a frequent challenge in the process measurement and control field. 

Industrial processes commonly are associated with corrosive or toxic fluids, often at extreme pressure or temperature and containing various levels of solids. Any of these traits can pose substantial risk to process performance and uptime. Operations that process fluids will employ pressure measurement devices to monitor process performance and maintain system safety levels. There are many instances where characteristics of the process and its media are not compatible with pressure measurement devices. Here are some potentially problematic scenarios for pressure measurement instruments: 

• Corrosive media that will prematurely deteriorate the pressure sensing element. 
• Viscous or fibrous media, also those that may crystallize or polymerize, posing a risk of clogging channels, tubes, and orifices of pressure measurement devices. 
• Media temperature that is beyond the rated range for the pressure measurement device has a potential to damage the instrument or cause error in the pressure reading. 
• A measuring point that is remotely located from where a technician may need to observe the reading. Also conceivable, the pressure measurement device needs to be located away from other potentially damaging environmental conditions. 
• The process requirements dictate specific hygienic requirements that are cause for the measurement device to be isolated from the medium. 
• Toxic or otherwise hazardous media that must be contained. 
• Excursions of system pressure may exceed the acceptable range of the instrument, potentially damaging the device. 

Threaded diaphragm seal
Courtesy Wika

A solution which can provide protection from the items listed above, while still maintaining instrument response and accuracy is a diaphragm seal. Seals are placed between the pressure measurement device and the process media. The space between the diaphragm, which is flexible, and the sensor is filled with a fluid that will hydraulically transfer the pressure condition on the process side of the diaphragm to the sensor. The diaphragm serves as a physical barrier between the potentially damaging media and the instrument. Diaphragm seals are available in a wide variety of configurations to accommodate any media type or connection requirement.

Seal selection involves specifying the connections and form factor to properly mate the diaphragm with the instrument and the process, then selecting the diaphragm material that will be compatible with the media. The best way to achieve a positive solution is to share your requirements with a qualified assembler. They can help select the right diaphragm seal and mate it up with a pressure gauge, providing a complete assembly that is ready to be installed in your process.

Innovations In RTD Signal Conditioning - One Manufacturer's Compilation

RTD Signal Conditioning Units
Courtesy Acromag

Temperature measurement may be one of the oldest components of process control and laboratory research. The measurement of temperature has progressed through a variety of methodologies, some of which are still in use today. Modern industrial process control relies heavily on the use of RTDs (resistance temperature detector) for their accuracy and stability.

Some of us have used RTDs in our process designs for many years, maybe without recognizing the innovations that have come about in the signal conditioning portion of our installations. One manufacturer of industrial signal conditioning equipment, Acromag, has compiled the ten most significant recent advances in RTD signal conditioning. I have included their white paper below.

Browse the paper, as it is brief and informative. You will likely see a few improvements of which you were unaware. Share your temperature measurement and signal conditioning challenges with an application specialist. Combining your process experience with their product application expertise will produce positive solutions.

Top Ten Advances In RTD Signal Conditioning from MSJacobs-Cali

Ethernet I/O Modules Provide Connectivity Advantages

Industrial Ethernet I/O Modules
Courtesy Acromag

Industrial process control relies on the accurate and timely delivery of process measurements and data to the point of control and decision making. As technology affords more opportunities to measure and transmit process variables, the demand for incorporating the additional information in the control and decision making process expands. The frequency at which data can flow from a process has also increased dramatically, and there is often significant value derived from rapid sampling. Transmitting the voluminous measurement data to the point of control can be accomplished using three basic methods:

• Point to point wiring from each measurement device to the control point.
• Wireless linkup from measurement location to controller.
• Wired network connection between measurement and control devices.

Each of these connection topologies has particular attributes which may better suit a particular application.  For a wired network scheme, Acromag has designed a line of I/O modules that make installation and configuration a smooth operation. Helpful features include:

• Power wiring options that allow back connected bus power or top mounted screw terminals. You can even provide primary and backup power sources to the two connections.
• Front facing screw terminals for connections make status checking of inputs a simple operation with your digital volt meter.
• Modules are rail mounted and can be placed immediately adjacent to one another for high density installation.
• Modules have a built in webpage for display of operational information. Configuration is accomplished using a front mounted USB port.
• Operable in temperatures -40 to +70 deg. Celsius.
• Two Ethernet ports on each unit allow modules to be daisy chained, reducing or negating need for local hubs.
• Acromag's Priority Channel Technology assures that data update frequencies are maintained, regardless of other network traffic.

The short video below provides additional detail on the useful features of the Acromag line of industrial Ethernet I/O modules. Watch the video. Share your process measurement and control connectivity challenges with a sales engineer specializing in industrial Ethernet I/O. Combine your process knowledge with the state of the art product knowledge of a product specialist for the best solutions.

Flexible Hazardous Gas Detection Monitoring System

Sentry IT Controller For Hazardous Gas Detection Monitoring
Courtesy Sierra Monitor

Industrial processes, by their scale and nature, are rife with hazards. As a process designer, engineer, or operator, protection of the facility, employees, and surrounding community ranks highest among our many responsibilities. Some hazards are apparent, visible, easily detected. Others are not. Technology and ingenuity play a substantial role in providing acceptable levels of safety in modern facilities.

Properly designing a hazardous gas monitoring system starts with identifying the target elements and their sources. Gaseous hazards can generally be divided into three general classes, all of which can be specifically targeted with a properly configured gas monitoring system.

• Combustible gas concentrations subject to ignition and explosion.
• Toxic gas with inherent personnel risk.
• Insufficient oxygen levels to support human respiration.

The best overall system configuration can be achieved through a combination of detectors, communications, and response that will provide accurate sensing of the target hazard, reliable and predictable transmission of information, and preconfigured response when alarm limits are triggered. Some product features for the detector monitor that may prove useful in a well specified installation:

• A means to non-intrusively calibrate all sensors at the same time
• Ability to diagnostically monitor connected sensors for performance.
• Provision of an easily operable interface for users.
• Battery backup to maintain operation during a power outage.
• Network and protocol compatibility with a range of industry accepted standards.
• Simple means to upgrade operating software.
• Compatibility with detection devices from a broad array of sources.
• Input capacity for more sensors than your current requirement.

I have included a bulletin describing such a unit, manufactured by Sierra Monitor. Browse the document and contact a hazardous gas detection application specialist to get more details and discuss your hazardous gas detection challenges. The best solutions come from combining your process knowledge and experience with that of a product application specialist.

Sierra Monitor Sentry IT Controller from MSJacobs-Cali