Wednesday, July 30, 2008
Risk taking in the field... Is it worth it?
Wednesday, July 16, 2008
4-20 mA Current Loop Primer
Despite the fact that the currents (4-20mA) and voltages (+12 to +24V) present in a typical current loop application are relatively low, please keep in mind that all local and national wiring codes, along with any applicable safety regulations, must be observed. Also, this application note is intended to be used as a supplement to all pertinent equipment-manufacturers’ published data sheets, including the sensor/transducer, the transmitter, the loop power supply, and the display instrumentation.
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Saturday, July 12, 2008
Lessons in Electric Circuit Ebook Download
Just added a new ebook free at the download section entitled Lessons in Electric Circuits Reference. From useful equations to conversion factors to various trigonometric and calculus references to circuit codes and symbols, all are available here in this awesome free ebook.
With 161 pages of pure electrical references and information, you could ask nothing more in this field.
In portable document format (format) for compatibility and ease of printing to a hard copy.
Download now at this page's download section!
Thursday, July 10, 2008
What are Pressure Transmitters
Pressure transducers are devices that convert the mechanical force of applied pressure into electrical energy. This electrical energy becomes a signal output that is linear and proportional to the applied pressure. Pressure transducers are very similar to pressure sensors and transmitters. In fact, transducers and transmitters are nearly synonymous. The difference between them is the kind of electrical signal each sends. A transducer sends a signal in volts (V) or millivolt per volt (mV/V), and a transmitter sends signals in milliamps (mA).
Both transmitters and transducers convert energy from one form to another and give an output signal. This signal goes to any device that interprets and uses it to display, record or alter the pressure in the system. These receiving devices include computers, digital panel meters, chart recorders and programmable logic controllers. There are a wide variety of industries that use pressure transducers and transmitters for various applications. These include, but are not limited to, medical, air flow management, factory automation, HVAC and refrigeration, compressors and hydraulics, aerospace and automotive.
There are important things to consider when deciding what kind of pressure transducer to choose. The first consideration is the kind of connector needed to physically connect the transducer to a system. There are many kinds of connectors for different uses, including bulletnose and submersible connectors, which have unique applications. Another important part is the internal circuitry of the transducer unit, which is housed by a "can" that provides protection and isolates the electronics. This can be made of stainless steel or a blend of composite materials and stainless steel. The various degrees of protection extend from nearly no protection (an open circuit board) to a can that is completely submersible in water. Other kinds of enclosures safeguard the unit in hazardous areas from explosions and other dangers.
The next thing to consider is the sensor, which is the actual component that does the work of converting the physical energy to electrical energy. The component that alters the signal from the sensor and makes it suitable for output is called the signal conditioning circuitry. The internal circuitry must be resistant to harmful external energy like radio frequency interference, electromagnetic interference and electrostatic discharge. These kinds of interferences can cause incorrect readings, and are generally to be avoided when doing readings. Overall, pressure transducers are well-performing and high-accuracy devices that make life easier for many industries.
Wednesday, July 09, 2008
New Download Section...
Hi!
Just recently added a download section of this site for free items related to Industrial Technology. I will be offering free ebooks and references as well as applications and other software. You can also request items by either contacting me through the chat box or through my email for more privacy. I am a research junkie and had already at my hand hundreds of softwares and ebooks related to this field. Enjoy!
d4rkhowl
What is OPC Server Development?
An OPC Sever is a software application that acts as an API (Application Programming Interface) or protocol converter. An OPC Server will connect to a device such as a PLC, DCS, RTU, etc or a data source such as a database, HMI, etc and translate the data into a standard-based OPC format. OPC compliant applications such as an HMI, historian, spreadsheet, trending application, etc can connect to the OPC Server and use it to read and write device data. An OPC Server is analogous to the roll a printer driver plays to enable a computer to communicate with an ink jet printer. An OPC Server is based on a Server/Client architecture.
There are many OPC Server Development toolkits available for developing your own OPC Server; MatrikonOPC's Rapid OPC Creation Kit (ROCKit) is one of it and enables quick OPC Server development. ROCKit offers a flexible and affordable solution that enables programmers to fully control their own product.
OPC ROCKit packages the complete OPC interface into a single DLL, eliminating the need to learn the complexities of Microsoft COM, DCOM or ATL. A developer simply writes the communication protocol routines for the underlying device and ROCKit takes care of the OPC issues.
Features include:
- Fully compliant with OPC DA 1.0a, 2.05 and 3.0 specifications.
- Free threading model on Windows NT, 2000 and XP platforms.
- Supports self-registration, browsing, data quality reporting, and timestamps.
- Can be used as a stand-alone server or as a service.
- In-proc server design for high-performance communication.
- Sample application code and comprehensive documentation illustrating how to use the ROCKit.
- OPC Explorer client that exercises the OPC COM interface for testing and debugging your server.
- The interface to the Device Specific Plug-in application code is separate from the OPC COM interface code. This means that future OPC source code updates are simply plugged in, while your own protocol code remains untouched, resulting in minimal engineering effort.
OPC (OLE for Process Control) Overview
Adding the OPC specification to Microsoft's OLE technology in Windows allowed standardization. Now the industrial devices' manufacturers could write the OPC DA Servers and the software (like Human Machine Interfaces HMI ) could become OPC Clients.
The benefit to the software suppliers was the ability to reduce their expenditures for connectivity and focus them on the core features of the software. For the users, the benefit was flexibility. They don't have to create and pay for a custom interface. OPC interface products are built once and reused many times, therefore, they undergo continuous quality control and improvement.
The user's project cycle is shorter using standardized software components. And their cost is lower. These benefits are real and tangible. Because the OPC standards are based in turn upon computer industry standards, technical reliability is assured.
The original specification standardized the acquisition of process data. It was quickly realized that communicating other types of data could benefit from standardization. Standards for Alarms & Events, Historical Data, and Batch data were launched.
Current and emerging OPC Specifications include:
Specification | Description |
OPC Data Access | The originals! Used to move real-time data from PLCs, DCSs, and other control devices to HMIs and other display clients. The Data Access 3 specification is now a Release Candidate. It leverages earlier versions while improving the browsing capabilities and incorporating XML-DA Schema. |
OPC Alarms & Events | Provides alarm and event notifications on demand (in contrast to the continuous data flow of Data Access). These include process alarms, operator actions, informational messages, and tracking/auditing messages. |
OPC Batch | This specification carries the OPC philosophy to the specialized needs of batch processes. It provides interfaces for the exchange of equipment capabilities (corresponding to the S88.01 Physical Model) and current operating conditions. |
OPC Data eXchange | This specification takes us from client/server to server-to-server with communication across Ethernet fieldbus networks. This provides multi-vendor interoperability! And adds remote configuration, diagnostic and monitoring/management services. |
OPC Historical Data Access | Where OPC Data Access provides access to real-time, continually changing data, OPC Historical Data Access provides access to data already stored. From a simple serial data logging system to a complex SCADA system, historical archives can be retrieved in a uniform manner. |
OPC Security | All the OPC servers provide information that is valuable to the enterprise and if improperly updated, could have significant consequences to plant processes. OPC Security specifies how to control client access to these servers in order to protect this sensitive information and to guard against unauthorized modification of process parameters. |
OPC XML-DA | Provides flexible, consistent rules and formats for exposing plant floor data using XML, leveraging the work done by Microsoft and others on SOAP and Web Services. |
OPC Complex Data | A companion specification to Data Access and XML-DA that allows servers to expose and describe more complicated data types such as binary structures and XML documents. |
OPC Commands | A Working Group has been formed to develop a new set of interfaces that allow OPC clients and servers to identify, send and monitor control commands which execute on a device. |
Tuesday, July 08, 2008
What are Temperature Transmitters
Temperature transmitters, RTD, convert the RTD resistance measurement to a current signal, eliminating the problems inherent in RTD signal transmission via lead resistance. Errors in RTD circuits (especially two and three wire RTDs) are often caused by the added resistance of the leadwire between the sensor and the instrument. Transmitter input, specifications, user interfaces, features, sensor connections, and environment are all important parameters to consider when searching for temperature transmitters, RTD.Transmitter input specifications to take into consideration when selecting temperature transmitters, RTD include reference materials, reference resistance, other inputs, and sensed temperature. Choices for reference material include platinum, nickel or nickel alloys, and copper. Platinum is the most common metal used for RTDs - for measurement integrity platinum is the element of choice. Nickel and nickel alloys are very commonly used metal. They are economical but not as accurate as platinum. Copper is occasionally used as an RTD element. Its low resistivity forces the element to be longer than a platinum element. Good linearity and economical. Upper temperature range typically less than 150 degrees Celsius. Gold and Silver are other options available for RTD probes - however their low resistivity and higher costs make them fairly rare, Tungsten has high resistivity but is usually reserved for high temperature work. When matching probes with instruments - the reference resistance of the RTD probe must be known. The most standard options available include 10 ohms, 100 ohms, 120 ohms, 200 ohms, 400 ohms, 500 ohms, and 1000 ohms. Other inputs include analog voltage, analog current, and resistance input. The temperature range to be sensed and transmitted is important to consider.Important transmitter specifications to consider when searching for temperature transmitters, RTD, include mounting and output. Mounting styles include thermohead or thermowell mounting, DIN rail mounting, and board or cabinet mounting. Common outputs include analog current, analog voltage, and relay or switch output. User interface choices include analog front panel, digital front panel, and computer interface. Computer communications choices include serial and parallel interfaces. Common features for temperature transmitters, RTD, include intrinsically safe, digital or analog display, and waterproof or sealed. Sensor connections include terminal blocks, lead wires, screw clamps or lugs, and plug or quick connect. An important environmental parameter to consider when selecting temperature transmitters, RTD, is the operating temperature.
Friday, July 04, 2008
What is a Control System?
In the case of linear feedback systems, a control loop, including sensors, control algorithms and actuators, is arranged in such a fashion as to try to regulate a variable at a setpoint or reference value. An example of this may increase the fuel supply to a furnace when a measured temperature drops. PID controllers are common and effective in cases such as this . Control systems that include some sensing of the results they are trying to achieve are making use of feedback and so can, to some extent, adapt to varying circumstances. Open-loop control systems do not directly make use of feedback, but run only in pre-arranged ways.
Pure logic controls were historically implemented by electricians with networks of relays, and designed with a notation called ladder logic. Nowadays, most such systems are constructed with programmable logic controllers.
Logic controllers may respond to switches, light sensors, pressure switches etc and cause the machinery to perform some operation. Logic systems are used to sequence mechanical operations in many applications. Examples include elevators, washing machines and other systems with interrelated stop-go operations.
Logic systems are quite easy to design, and can handle very complex operations. Some aspects of logic system design make use of Boolean logic.
Controller System for Industrial Automation
Digital controllers do not have mechanical moving parts. Instead, they use processors to calculate the output based on the measured values. Since they do not have moving parts, they are not susceptible to deterioration with time. Digital controllers are not continuous. They execute at very high frequencies, usually 2-3 times a second.
Analogue controllers should not be confused with pneumatic controllers. Just because a controller is analogue does not mean it is pneumatic. Pneumatic controllers are those that use instrument air to pass measurement and controller signals instead of electronic signals. An analogue controller can use electronic signals. Compared to pneumatic controllers, electronic controllers (can be analogue or digital) have the advantage of not having the same amount of deadtime and lag due to the compressibility of the instrument air.
Wednesday, July 02, 2008
Measurements
Measurement
With the advent of computers, it is now possible to do inferential measurements, meaning telling the value of a parameter without actually measuring it physically. It should however, be remembered that inferential measurement algorithms are also based on physical measurements. Therefore, rather than rendering measurements redundant, they have made measurements all the more important.
All pressure measurement systems consist of two basic parts: a primary element, which is in contact, directly or indirectly, with the pressure medium and interacts with pressure changes; and a secondary element, which translates this interaction into appropriate values for use in indicating, recording and/or controlling.
An electronic-type transmitter is shown in the figure above. This particular type utilizes a two-wire capacitance technique.
Process pressure is transmitted through isolating diaphragms and silicone oil fill fluid to a sensing diaphragm in the center of the cell. The sensing diaphragm is a stretched spring element that deflects in response to differential pressure across it. The displacement of the sensing diaphragm is proportional to the differential pressure. The position of the sensing diaphragm is detected by capacitor plates on both sides of the sensing diaphragm. The differential capacitance between the sensing diaphragm and the capacitor plates is converted electronically to a 4-20 mA dc signal.
Numerous types of flowmeters are available for closed-piping systems. In general, the equipment can be classified as differential pressure, positive displacement, velocity and mass meters.
Differential pressure devices include orifices, venturi tubes, flow tubes, flow nozzles, pitot tubes, elbow-tap meters, target meters, and variable-area meters.
Positive displacement meters include piston, oval-gear, nutating-disk, and rotary-vane types. Velocity meters consist of turbine, vortex shedding, electromagnetic, and sonic designs.
Temperature Measurement
How can I measure temperature?
Temperature can be measured via a diverse array of sensors. All of them infer temperature by sensing some change in a physical characteristic. Six types with which the engineer is likely to come into contact are: thermocouples, resistive temperature devices (RTDs and thermistors), infrared radiators, bimetallic devices, liquid expansion devices, and change-of-state devices.