Yokogawa Pressure Handbook: A Basic Guide to Understanding Pressure

Pressure, temperature, level and flow are the four common plant measurements. Of the four, pressure is the most fundamental and common. The three remaining measurements can be inferred from pressure-flow (orifice plates, pitot tube, venturi), level (hydrostatic ‘Head’ pressure), and temperature (pressure thermometer). It can even be used to infer density (pressure for a given volume) and weight (load cells). If you cannot measure it, you cannot control it.

The ability to quickly, accurately, and reliably measure pressure is invaluable when trying to control a process.

Each of these types of transmitters measures pressure. The ow transmitter, liquid level transmitter, and pressure thermometer use the measured pressure to infer another process parameter.

Read the handbook below to garner a great understanding of industrial pressure measurement.

For more information on any industrial pressure requirement, visit http://www.powerspecialties.com or call (816) 353-6550.

CIP Sanitary RTD Sensors

CIP Sanitary RTD Sensors
CIP (clean-in-place) Sanitary RTD Sensors 
General purpose CIP (clean-in-place) sanitary connector RTD temperature sensors are used in processing applications where sensor corrosion and product contamination are critical factors. These sensors must meet or exceed finish specifications set forth by the 3A Sanitary Council Standard.

General-purpose CIP sanitary-connected RTD temperature sensors are used in food, dairy, beverage, pharmaceutical, and chemical processing applications where sensor corrosion and product contamination are critical factors. Sanitary caps are most commonly used in such processes. Sanitary caps are welded to the sheath and to a heavier support tube, all made of stainless steel, and then ground and polished to a finish that exceeds the No. 4 minimum finish required by the 3-A Sanitary Standard 74 - .

Assemblies are supplied with a surface finish that meets or exceeds 32µin Ra. Surface finishes of 15µin Ra or better are available upon request. The process contact surfaces are free of pits, crevices, and pockets thus preventing corrosion and bacteria growth. The 3-wire constructed sensor assembly consists of a high-accuracy platinum element sealed inside a 316 stainless steel sheath, and is provided with a FDA-compliant white thermoplastic gasketed connecting head. The complete assembly provides excellent wash-down protection.

It is recommended that once customer connections are made, the connecting terminals be further protected by applying a coating of moisture-proof sealant over the connections.

For assistance in choosing the right CIP sanitary RTD sensor visit http://www.powerspecialties.com or contact Power Specialties at (816) 353-6550.

Precision Weighing at High Speeds in Industrial Process Control

BLH Nobel G5 DIN Rail Mount
BLH Nobel G5 DIN Rail Mount
Industrial process control implies the presence of industrial process measurement. Throughout our operations, we seek to measure "how much" of something is present. In the case of many materials, weight is the preferred measurement.

Weight is a measurement of force. We can use it as a statement of "how much" because gravity is considered constant across the planet surface. The force or weight measured for a batch of material at a shipping point in the US will, for commercial purposes, be the same force or weight measured for that material at any destination to which it may be delivered. Measurement of weight can be used for establishing proper mixing ratios of components to be combined in a particular manner. The level of material in a tank or other container can be ascertained through a measurement of weight.

BLH/Nobel Weighing Systems manufactures a high speed, high performance control for industrial weight/force measurement applications. Their G5 line of controllers provides the user a wide range of configurable options, from multiple input channels to analog and digital outputs. The clean user interface provides access to all functions and channels and the unit is available as a freestanding desktop, DIN rail mount, or panel mount unit. There is also a model configured for harsh environments.

The brochure below provides a good overview of the unit and its potential applications. Contact a BLH Nobel product specialist to receive more details, or to discuss how the G5 and other BLH/Nobel Weighing Systems products might be helpful to your process operation.

Continuous Liquid Level Measurement Technologies Used in Industry

Industrial Level Measurement
Industrial Level Transmitters
(courtesy of Hawk Measurement)
Although continuous level measurement technologies have the ability to quantify applications for bulk solids, slurries, and granular materials, liquid level technologies stand out as being exceptionally crucial to the foundation of process control. Called transmitters, these continuous liquid level measurement devices employ technologies ranging from hydrostatics to magnetostriction, providing uninterrupted signals that indicate the level of liquid in a vessel, tank, or other container.

Hydrostatic devices focus on the equilibrium of dynamic and static liquids. There are three main types of hydrostatic transmitters:
  1. displacer
  2. bubbler
  3. differential pressure.
The displacer transmitters utilize a float placed within the liquid container. With its buoyancy characterized to the liquid and the application, the float, a connecting stem, and a range spring or similar counterbalance represents the liquid level in terms of the movement of the displacer (float). The displacement, or movement, of the assembly is converted into an electric signal for use by the monitoring and control system.

Bubbler transmitters are used for processing vessels that operate at atmospheric pressure. This method introduces a purge gas or an inert gas, e.g. air or dry nitrogen, into a tube extending into the liquid vessel. Precise measurement of the pressure exerted on the gas in the dip tube by the liquid in the tank is used to determine the height of the liquid.

Differential pressure (DP) transmitters rely directly on, in a basic explanation, the pressure difference between the bottom and top of the container. Precise pressure measurement is used to determine the height of the liquid in the tank. One of the most advantageous aspects of DP transmitters is that they can be used in pressurized containers, whereas displacer and bubbler transmitters cannot.

Other examples of level transmitter technologies which are not hydrostatic devices are magnetostrictive, capacitance, ultrasonic, laser, and radar.

Mag gage with magnetostrictive level transmittersIn magnetostrictive level transmitters the measuring device, a float, has a series of magnets that create a magnetic field around a wire enclosed in a tube. Electrical pulses sent down the wire by the transmitter head product a torsional wave related to the position of the float, which moves with changes in liquid surface level. The transit time of the torsion wave back to the sensing head is measured and the depth of the liquid, as indicated by the float position, can be determined.

Capacitance transmitters are best applied to liquids that have high dielectric constants. Essentially, changes in the capacitance of the sensor / tank / liquid assembly will vary proportionately with the liquid level. The change in capacitance is measured and converted to an appropriate electrical signal.

Ultrasonic level transmitters emit ultrasonic energy from the top of the vessel toward the liquid. The emissions are reflected by the liquid surface and them time required for the signal to return to the source is used to determine the distance to the liquid surface.

Laser level transmitters operate similarly to an ultrasonic level transmitter. However, instead of using ultrasound signals, they use pulses of light.

Radar level transmitter
Radar Level
Radar level transmitters involve microwaves emitting downward from the top of the container to the liquid's surface and back again; the measurement is the entire time-frame. One variable radar level measurement echoes capacitance measurements: they both involve dielectric contact of liquid.

The precise measurement of transmit time for a wave or pulse of energy is employed in several of the technologies, the measurement of pressure in others. Each technology has a set of attributes making it an advantageous selection for a particular range of applications. Share your liquid level measurement challenges with an application expert, combining you process knowledge with their product application expertise to develop effective solutions.