Showing the Difference in Function Between High and Low Pressure Ports on a Differential Pressure Transmitter
The following video demonstrates the different responses of a differential pressure transmitter to both positive and negative pressures applied to its high and low pressure ports. The response of pressure and vacuum to the "high" port is opposite the effect of pressure and vacuum (respectively) applied to the "low" port.
Industrial Temperature Sensors and Indicators
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| Variety of electrical temperature sensors (Pyromation) |
Temperature sensors are devices which are used to temperature measurement of a medium (i.e. liquid, solid or gas). The sensor detects change in the temperature, and accordingly, change its physical or electrical property in a manner that can be measured. These sensors come in many different forms and are used for a wide variety of applications.
We as human’s simply sense temperature as hot or cold, but in process control, precise measurement of temperature is required in order to control a process efficiently. Accordingly, the correct temperature sensing device needs to be properly selected.
Types of Temperature Sensors
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| Vapor actuated temperature indicator (REOTEMP) |
Devices that use the physical expansion and contraction of materials (like non-compressable fluids,
vapors, or differential metals) to mechanically open or close a set of contacts.
- Examples of mechanical temperature sensors are bulb and capillary thermostats, thermometers, mechanical temperature switches, and bi-metallic thermostats.
These sensors undergo a measurable electrical change such as resistance, voltage, or current proportional to a given change in temperature.
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| Temperature Probe Assembly |
- Examples are thermocouples which generate a micro-voltage based upon a temperature differential between two dissimilar metals; RTDs that increase resistance as the sensing temperature increases; and thermistors, which dramatically decrease resistance as temperature increases.
For more information on temperature sensors, contact Power Specialties at (816) 353-6550 or visit http://www.powerspecialties.com.
Basics of Rotameters (Variable Area Flowmeters)
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| Rotameter (Yokogawa) |
The variable area flowmeter is an instrument for metering the flowrate of liquids and gases in a pipeline. It includes a vertically oriented conical tube, whose diameter is larger at the top than at the bottom, through which the fluid flows upward and in which a vertically moving float is positioned. The height of the float in the tube increases as the flowrate increases in such a manner that the resistance to the flow is always balanced by the weight of the float and remains constant regardless of the flowrate. The height of the float in the tube is a measure of the flowrate.
The value of the flowrate can be read from a scale. Variable area flowmeters are the most cost effective solution for almost all applications involving the measurement of industrial process liquids, gases or steam. They meet the application requirements by featuring a wide range of design varieties and sizes.
Rotameters offer long life and high reproducibility and are excellent mechanical back-up meters because no external power supply is needed. For more information on rotameters (variable area flowmeters) visit http://www.powerspecialties.com or call Power Specialties at (816) 353-6550.
The video below does a great job introducing the various types and uses for rotameters.
The Bubbler Method of Liquid Level Measurement
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| Bubbler Level Measurement (courtesy of Yokogawa) |
Determining liquid level using a hydrostatic pressure measurement is a simple, easy to implement strategy for delivering a continuous level signal to the process operating and control system.
There can be situations where mounting the measuring gear near the bottom of a tank or other vessel may be impractical or undesirable. A pressure transmitter mounted low on a tank may expose it to damage from plant traffic or other physical hazards. It is also possible that the tank may not have a suitable fitting located low enough to provide the needed measuring range. Having a potential leakage point at a fitting low on the tank may also be undesirable. Another, and certainly not final, scenario would be an application involving a corrosive liquid which must not come in contact with the pressure sensor.
The bubbler method of liquid level
measurement employs an arrangement that overcomes all of the previously
mentioned impediments. It can utilize connections at the top of the
tank, above the liquid level. The way in which the method works will
keep the pressure sensor out of contact with the process liquid,
providing isolation from potential corrosive effects.
The apparatus for level measurement using the bubbler method employs a simple dip tube that extends from the pressure sensor or transmitter to nearly the bottom of the tank or vessel. A small amount of purge air or gas continually flows through the dip tube and will bubble out the bottom of the tube. This dip tube arrangement essentially transfers the hydrostatic pressure at the bottom opening of the tube to the pressure transmitter, while the purge gas keeps the liquid from advancing up into the pipe. The bubbler can be used on atmospheric or pressurized tanks with a properly configured pressure or differential pressure transmitter.
Probably the most significant application point of the bubbler method that will distinguish its use from many other level measurement methods is the importance of maintaining air or gas flow in the dip tube. The flow provides isolation of the sensor, but the flow must also be set to a level that will not impact the pressure measurement in the tube itself. If the flow is excessive, back-pressure in the tube can be offset from the level imparted by the tank contents, with the result being an incorrect measurement.
Below is an application note from Yokogawa, showing how their pressure transmitters and rotameters can be used to create the setup. Share your process measurement challenges and requirements with instrumentation experts, combining your own process knowledge with their product application expertise to produce effective solutions.
The apparatus for level measurement using the bubbler method employs a simple dip tube that extends from the pressure sensor or transmitter to nearly the bottom of the tank or vessel. A small amount of purge air or gas continually flows through the dip tube and will bubble out the bottom of the tube. This dip tube arrangement essentially transfers the hydrostatic pressure at the bottom opening of the tube to the pressure transmitter, while the purge gas keeps the liquid from advancing up into the pipe. The bubbler can be used on atmospheric or pressurized tanks with a properly configured pressure or differential pressure transmitter.
Probably the most significant application point of the bubbler method that will distinguish its use from many other level measurement methods is the importance of maintaining air or gas flow in the dip tube. The flow provides isolation of the sensor, but the flow must also be set to a level that will not impact the pressure measurement in the tube itself. If the flow is excessive, back-pressure in the tube can be offset from the level imparted by the tank contents, with the result being an incorrect measurement.
Below is an application note from Yokogawa, showing how their pressure transmitters and rotameters can be used to create the setup. Share your process measurement challenges and requirements with instrumentation experts, combining your own process knowledge with their product application expertise to produce effective solutions.
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.
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.
CIP Sanitary RTD Sensors
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| CIP (clean-in-place) Sanitary RTD Sensors |
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
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| BLH Nobel G5 DIN Rail Mount |
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.
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.
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