Archive for January, 2012

Flow Calibration

You can calibrate flow measurement devices by three methods: 1) wet calibration using actual fluid flow; 2) measurement check of physical dimensions and use of empirical gables relating flow rate to these dimensions; or 3) dry calibration using flow simulation by electronic or mechanical means.

It is common to make measurements using a combination of several instruments acting together. It is also appropriate to calibrate different portions of such a system by different methods. In the case of a flowmeter with a transmitter and an indicator, a common practice is to wet calibrate the flowmeter and separately dry calibrate the transmitter and indicator. You can often further separate the flowmeter itself into a wetted primary (the portion generating the flow signal) and a flow secondary (the portion providing the signal processing).

Whenever separately calibrating portions of a system, maintain adequate accuracy rations for each calibration and calculate the overall system accuracy by the previously described method.

January 7, 2012 at 9:00 am Leave a comment

Applying Coriolis Technology to High Pressure Applications

Measurement at high pressure needs heavy-duty metering

The first commercially available Coriolis flowmeter based upon the observed effects of mass flowing through vibrating tube systems appeared in the late 1970s, early 1980s. Any mass flowing through such tubes causes dampening and distortion effects in the tubing system, which correlates to the actual flow in the piping. Today, many Coriolis mass flowmeters in use employ this technology, with about a dozen different manufacturers producing them. All of these meters are built on a vibrating piping system with the inertia of the mass of material flowing through creating very small but measurable deflections of the tubing.

The name for these meters comes from the force responsible for the deflections—the Coriolis force. Compared to other technologies, which mostly determine flow velocity, Coriolis mass flowmeters offer direct mass flow measurement, and unlike velocity measurement techniques, changes in density, viscosity, and flow profile do not, in general, play a significant role when measuring flow with a Coriolis meter.


January 7, 2012 at 8:50 am Leave a comment

Temperature Instrumentation Problems and Solutions in Industrial Processes

Despite many advances in electronics and computer technologies, industrial facilities still measure most temperature with conventional sensors, such as thermocouples and resistance temperature detectors (RTDs)—technologies whose basic designs are more than 50 years old. Though so-called smart sensors are now available, the “smartness” of the sensor lies mostly in its electronics and memory and in its ability to adjust its output remotely using digital technology. The same is true for wireless sensors. They usually measure temperature with a conventional sensing device but transmit the information to a remote location with wireless technology.

Though manufacturers have made great advances in producing essentially drift-free electronics for temperature sensors, no new sensor technology lies on the horizon promising significantly new drift-free, sturdy sensors that can readily tolerate the temperature, humidity, and vibration environments found in industrial processes. For this reason, today’s instrumentation or sensor problems, for example sensor drift, are similar to those of a generation ago. Moreover, questions still linger over how plants can objectively assess the accuracy, response time, residual life, and other characteristics of their installed instrumentation. This article examines some problems involving temperature sensors and offers practical ways to identify, assess, and resolve them.


January 7, 2012 at 8:42 am Leave a comment

Pressure is a fundamental variable in process control systems that impacts safety, quality, and productivity

Pressure is a fundamental measurement from which other variables can be inferred. Pressure values rank with those of voltage and temperature in defining the energy (primarily potential) or state of matter. Temperature is the potential for doing thermodynamic work, voltage is the potential for doing electrical work, and pressure is the potential for doing fluidic work. The importance of pressure measurement is demonstrated by the need for transmitting signals powering equipment, inferring fluid flow in pipes, and using filled thermal systems in some temperature applications. Liquid levels in tanks and other vessels also can be inferred from pressure quantities.


January 7, 2012 at 8:34 am Leave a comment

Advances in Flow and Level Measurements Enhance Process Knowledge, Control

Smart measurements help analyze, diagnose, predict, control, and optimize process performance

Jobs in research, process development, process design, process technology, automation, operations, or maintenance depend upon the ability to see, trend, analyze, diagnose, and collect the information from measurements. Ultimately, what you want to know as an engineer or technician is “why.” Modern instruments have made great progress in not only answering “why” but also offering a higher level of plant performance. The material balance is at the core of the process and the “why.” Flow and level measurements determine the material balance, and hence, process behavior.

More obvious is the performance and integrity of control systems and safety systems depend upon the accuracy, reliability, and speed of the measurements. You cannot control or protect something you cannot measure.

January 7, 2012 at 8:23 am 1 comment

Pressure Measurement in Industrial Applications

Next to temperature, pressure is the second most common measurement in process plants, and temperature and pressure measurement often go hand-in-hand in industrial applications.

Today’s high tech pressure measurement techniques are far more advanced than they were in the old days of manometers, bourdon tubes, and bellows. Modern pressure transmitters are extremely accurate and include smart electronics, built-in diagnostics, and a host of connectivity options. But one thing remains the same, and that is the physics behind the measurement. (more…)

January 7, 2012 at 8:13 am Leave a comment

Boiler Drum Level Control

Drum level control is critical to good boiler operation, as well as safe boiler operation

The drum level must be controlled to the limits specified by the boiler manufacturer. If the drum level does not stay within these limits, there may be water carryover. If the level exceeds the limits, boiler water carryover into the superheater or the turbine may cause damage resulting in extensive maintenance costs or outages of either the turbine or the boiler. If the level is low, overheating of the water wall tubes may cause tube ruptures and serious accidents, resulting in expensive repairs, downtime, and injury or death to personnel. A rupture or crack most commonly occurs where the tubes connect to the drum. Damage may be a result of numerous or repeated low drum level conditions where the water level is below the tube entry into the drum.

Some companies have had cracked or damaged water tubes as a result of time delayed trips or operators having a trip bypass button. When the drum level gets too low, the boiler must have a boiler trip interlock to prevent damage to the tubes and cracks in the tubes where they connect to the boiler drum. The water tubes may crack or break where they connect to the drum, or the tubes may rupture resulting in an explosion. The water tube damage may also result in water leakage and create problems with the drum level control. The water leakage will affect the drum level because not all the water going into the drum is producing steam. (more…)

January 7, 2012 at 8:00 am Leave a comment

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