What is Inferential Measurement? An Understanding Through Differential Pressure Level Control

Level control using delta-P transmitter.*

Differential pressure transmitters are utilized in the process control industry to represent the difference between two pressure measurements. One of the ways in which differential pressure (DP) transmitters accomplish this goal of evaluating and communicating differential pressure is by a process called inferential measurement. Inferential measurement calculates the value of a particular process variable through measurement of other variables which may be easier to evaluate. Pressure itself is technically measured inferentially. Thanks to the fact numerous variables are relatable to pressure measurements, there are multiple ways for DP transmitters to be useful in processes not solely related to pressure and vacuum.

An example of inferential measurement via DP transmitter is the way in which the height of a vertical liquid column will be proportional to the pressure generated by gravitational force on the vertical column. The differential pressure transmitter measures the pressure exerted by the contained liquid. That pressure is related to the height of the liquid in the vessel and can be used to calculate the liquid depth, mass, and volume. The gravitational constant allows the pressure transmitter to serve as a liquid level sensor for liquids with a known density. A true differential pressure transmitter also enables liquid level calculations in vessels that may be pressurized.

Gas and liquid flow are two common elements maintained and measured in process control. Fluid flow rate through a pipe can be measured with a differential pressure transmitter and the inclusion of a restricting device that creates a change in fluid static pressure. In this case, the pressure in the pipe is directly related to the flow rate when fluid density is constant. A carefully machined metal plate called an orifice plate serves as the restricting device in the pipe. The fluid in the pipe flows through the opening in the orifice plate and experiences an increase in velocity and decrease in pressure. The two input ports of the DP transmitter measure static pressure upstream and downstream of the orifice plate. The change in pressure across the orifice plate, combined with other fluid characteristics, can be used to calculate the flow rate.

Process environments use pressure measurement to inferentially determine level, volume, mass, and flow rate. Using one measurable element as a surrogate for another is a useful application, so long as the relationship between the measured property (differential pressure) and the inferred measurement (flow rate, liquid level) is not disrupted by changes in process conditions or by unmeasured disturbances. Industries with suitably stable processes - food and beverage, chemical, water treatment - are able to apply inferential measurement related to pressure and a variable such as flow rate with no detectable impact on the ability to measure important process variables.

* Image courtesy of T. Kuphaldt and his book "Lessons In Industrial Instrumentation"

Instrument Specialties, Inc. - ISI Technical Group

Instrument Specialties is in the business of helping customers improve and implement their processes and applications. A professional agency with a focused, creative, and aggressive staff, ISI takes a long term relationship approach to business.

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Teledyne ISCO accQlink™ Provides Water and Wastewater Plants Modular and Flexible Remote Data Acquisition

The Teledyne ISCO accQlink™ accepts multiple inputs, including RS232, RS485, SDI-12, analog, and/or contact output. The robust design includes autonomous field operation using battery, solar, or permanent power sources.  Data is accumulated from a variety of sensor types, transmitted securely, and stored either in cloud storage and/or a customer server. Data can be easily integrated into the facility SCADA system, modeling software, business intelligence platform, ISCO Flowlink Pro, or other software.

ISCO cloud server allows for the viewing and management of data from anywhere with an Internet connection. ISCO cloud server also includes a graphical data management Web User Interface and can be programmed to send text or email alerts at preprogrammed thresholds.

During data transmission from accQlink™, a built in Global SIM card chooses the strongest available cell signal and cell networks, ensuring maximum uptime. A yearly service plant includes all cell phone charges, data hosting, and web user interface. Finally, the accQlink™ offers digital communication options such as LPWAN (Low Power Wide Area Network), Bluetooth, and Satellite.

Applications:

• Overflow monitoring (CSO and SSO)
• I&I, cMOM, ad other collection system monitoring
• Wet well monitoring in Pump stations
• Stormwater runoff monitoring
• Weather monitoring
• Water quality monitoring

Standard Features:

• Rugged Design with IP 68 Enclosure
• Data encrytion for cyber security
• Cloud data hosting and intuitive Web UI
• Automatic alerts via SMS and email

For more information about the Teledyne ISCO accQlink™ contact Instrument Specialties by visiting https://isi.group or calling 407-324-7800.

Wireless Data Access For Water Quality Monitoring Instumentation

The Aqua Troll 500 provides wireless access to
multi-parameter water quality measurement.

Water quality monitoring, whether for environmental studies, research or regulatory compliance is an operation that can benefit from instruments that automate or otherwise increase the efficiency of sample collection, measurement and data storage.

In-Situ Inc., manufacturer of reliable, top quality water monitoring equipment, adds to their already comprehensive line of portable and fixed installation water quality measurement instruments with the Aqua Troll 500. The instrument is a multiparameter sonde that can be used as a handheld device, with data transmitted to a smartphone running the Android data collection app. For fixed installations, the Aqua Troll can be integrated wirelessly into a telemetry system to deliver collected data to remote stations.

Some applications include:

• Surface water spot sampling and profiling
• Remote monitoring via telemetry
• Long-term drinking water, wastewater or stormwater monitoring
• Aquaculture
• Low-flow groundwater sampling and remediation

Numerous features of the instrument are incorporated to decrease the amount of time required by technicians to put the instrument into operation and maintain it. The datasheet included below provides additional detail. Share your water quality measurement requirements and challenges with instrumentation experts. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Water Quality Wireless Monitoring Instrumentation from Instrument Specialties, Inc.

Mapping Gas and Flame Detectors to Deliver Accurate Coverage

Determining the proper location layout for hazardous gas
detectors is key to ensuring an acceptable level of safety.

MSA is committed to supporting operators of industrial facilities in their efforts to promote safe work environments that benefit employees, contractors and the community. Devices and instruments for flame and hazardous gas detection and monitoring are a part of the MSA family of safety products.

The ability to detect the presence and level of gases that may be hazardous is incorporated in physical devices and their function is well understood. The challenge faced by plant and facility operators is determining the locations for sensing devices throughout the facility that will provide an effective level of protection. MSA has a flame and gas mapping solution that employs quantitative models and actual facility conditions to provide a high level of confidence that overall target performance for flame and gas detection is achieved.

More information is provided in the document included below. Share your flame and gas detection challenges with the experts. Leverage your own knowledge and experience with their product application resources and develop a successful solution.

Gas and Flame Detector Mapping from Instrument Specialties, Inc.

Refrigerant Leakage Monitor for Multiple Refrigerants

Monitoring HVAC machinery spaces for the presence of leaked refrigerant is driven by compliance, economic and safety concerns. Refrigerant gas can displace oxygen and lead to unbreathable atmosphere in enclosed spaces. On the economic front, refrigerant is expensive, and leakage must be replaced. Additionally, slowly leaking refrigerant will eventually result in system charge levels that negatively impact system operation and performance.

The MSA Chillgard 5000 monitors the levels of up to six selected refrigerants, providing alerts in the machine space, as well as an external alarm and activation of mechanical ventilation. The sensing technology can detect levels as low as 1 ppm, providing earliest possible warning of an alert condition.

The short video demonstrates the features of the unit that deliver reliability, versatility, stability and ease of operation and maintenance. Share your refrigeration machinery room monitoring requirements and challenges with a product specialist. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Monitoring Stormwater Runoff

Schematic of stormwater runoff station instrument and
equipment setup.
Image courtesy Teledyne/ISCO

Rain rinses the local area surfaces, cleaning them and concentrating all the soils, chemicals, and other loosened substances in stormwater runoff. The chemical composition of stormwater runoff can be complex, depending upon the activities conducted in the collection area. Stormwater runoff ultimately ends up in surface waters, rivers, lakes, streams, swamps, bays and oceans.

Stormwater runoff has been identified as a major contributor to surface water pollution. The current regulatory climate makes increasing demands on a number of local, municipal and private entities to monitor and analyze stormwater runoff to gather data that supports pollution control efforts and environmental studies.

Configuring an active stormwater collection and measurement system can be challenging. Teledyne ISCO, experts in environmental monitoring, crafted an application note that summarizes the hardware requirements for a typical system to be placed in the field. The app not is included below, but best results for a particular application or system will be achieved by sharing your environmental monitoring challenges with instrumentation specialists. Leverage your own knowledge and experience with their product application expertise and develop an effective solution.

Active Stormwater Runoff Monitoring Instruments and Equipment from Instrument Specialties, Inc.