Optical wavelength division multiplexing (WDM) networking technology has been identified as a suitable candidate for future wide area network (WAN) environments, due to its potential ability to meet rising demands of high bandwidth and low latency communication. Networking protocols and algorithms are being developed to meet the changing operational requirements in future optical WANs (OWAN). Simulation is used in the study and evaluation of such new protocols, and is considered a critical component of protocol design. The optical WDM network simulator (OWns) facilitates the study of switching and routing schemes in WDM networks. OWns is designed as an extension to the network simulator ns a multi-protocol network simulator that is widely-used for networking research and available in the public domain. Our goal is to incorporate the key characteristics of WDM networks in the simulator, such as optical switching nodes, multi-wavelength links, virtual topology constructions, related switching schemes and routing algorithms.
Friday, January 16, 2009
Visual Data Analyzer
Using Visual Data Analyzer, business and data analysts can interactively visualize and analyze multi-dimensional data. We hope you give this a try and as always, tell us what you think!
Visual Data Analyzer
The Visual Data Analyzer prototype allows users to easily and interactively browse and understand what is happening in semantic, relational and OLAP data sources.
(See larger images: Data Realm Expression Editor, Pie Charts, Bar Charts, Scatter Plot)
Technical Description
This prototype supports various types of data sources, specifically: OLAP, Business Objects Universes, and/or custom sources (called "Data Realms").
The Visual Data Analyzer prototype includes two components:
- Data Realm Analyzer allows users to connect to and select data objects to place into either a multi-dimensional grid or to a sidebar that controls visualization attributes such as color, shape and size. The Analyzer visualization window automatically renders the correct visualization approach (bar, pie and scatter). You can reorient/pivot the displayed data by dragging and dropping data objects across grid axes, and you can select section/page members that provide context for the data.
- Data Realm Designer is a data shaping system that creates powerful Analyzer data spaces called Data Realms. Data Realms can join data from any supported source (relational or OLAP), joining underlying data and adding complex calculations. Queries and calculations on Data Realms are optimally re-expressed by the system into minimal queries on the underlying databases, including push-down calculation, with any remaining calculation being done locally. Data Realms can be joined with other Data Realms to increase the abstraction level, with the potential of adding calculated objects at every level.
Data Realms support the following data sources: Derby (which is bundled to provide an out-of-the-box sample), ODBC, and SQL Server 2000.
Visual Data Analyzer can be installed using Java Web Start (registration and login required). You will need Java 1.4 already installed.
See the manuals included in the install for how to get started. For more details on how the software works you may refer to the online Analyzer manual (PDF) and Designer manual (PDF). You can also view streaming videos of an Analyzer demonstration (WMV), a simple Designer demonstration (WMV) and an advanced Designer demonstration to learn more about what the software can do. We are always keen to receive feedback on our Labs content.
Wednesday, January 14, 2009
Analyzer 3.0 (alpha)
Analyzer is a fully configurable Network Analyzer for Win32. It includes several functionalities that are needed by network management operator. Analyzer is based on WinPcap and it is able to capture packets on most Win32 platforms (and link-layer technologies).
Analyzer 3.0 comes out with some event logging, LAN monitoring and traffic monitoring capabilities.
However, Analyzer 3.0 most valuable point is the ability to parse network packets according to the protocol description contained into some external files, which can be modified at run-time by the user. These files are written in the new NetPDL language; for who is interested in that, please read the Protocol Dissectors Section.
We moved the development of Analyzer to the SourceForge.net servers. You can use all their facilities for submitting a request, subscribing the mailing lists, browsing the latest code, and so on.
This program is current being developed at Politecnico di Torino and it is released under a BSD licence. The program is free, but we would like to receive a small contribution from all the companies that are using our tools for business. Please, be honest: if you get (or save) money from our work, let's share part of it with us.
What does Analyzer?
Analyzer is not a simple network sniffer. Here there is a brief summary of what it can do.
- Network Sniffer
- Analyzer can capture (and display) packets on both the local machine and remote probes, thanks to the full support of the Remote Capture functionality of WinPcap.
Additionally, one of the most valuable point is the ability to parse network packets according to the protocol description contained in external files, which can be modified at run-time by the user. These files are written in the new NetPDL language; for who is interested in that, please read the Protocol Dissectors Section. - Advanced sniffing capabilities
- Due to the full support of the WinPcap remote capture capabilities, Analyzer is able to display packets currently being captured on another (remote) host. This can be done even if the remote host is behind a firewall, thanks to the support of the Active Mode remote capture. Additionally, Analyzer supports also sampling in order to reduce the amount of traffic generated by the remote host toward Analyzer. Sampling is available also when capturing from a local interface.
- End-to-end Reachability Monitor
- Analyzer can monitor the reachability (through a set of ICMP ECHO, aka PING, packets) of remote host, saving data into a database and making additional statistics. The user can later retrieve historical data to see how the reachability of some host changed over time.
- Additionally the user can set some alarm (e.g. "send an e-mail") in case of some event (e.g. "host down").
- Local Network Host Monitor
- Analyzer can discover the presence of the active station on your local network and display their MAC, IPv4 and IPv6 addresses, and their canonical name.
This module can monitor the availability of the stations and signal whether an host is up, is down, and so on. Furthermore, it can detect address spoofing (e.g. when the same IPv4/IPv6 address appears to bind more than one MAC addresses). - Additionally the user can set some alarm (e.g. "send an e-mail") in case of some event (e.g. "possible spoofing").
- Network Sessions Logger
- Analyzer can monitor the presence of TCP/UDP/ICMP "sessions" over the network, saving a database record for each session detected within a time frame. A summary of the session is then saved into a database for later processing.
- Network Data Mining
- Analyzer is able to apply Data Mining techniques to the database of the sessions, created with the Network Sessions Logger (NetLogger). This module is able to find some relevant relationships over the data which may be unexpected and it is able to give an insight about how the network looks like (e.g. which are the servers, which are the clients, and more). Furthermore, it can compare the relationships that come out from two different NetLogger databases and display the differences (e.g. a new server has been added to the network).
- Event Handling
- Analyzer has a module that manages events associated to the other modules and it executes the appropriate actions. The number of events and the actions associated to them are customizable by the user.
WARNINGS
- Analyzer is a tool that is still under development. Please be patient when you use it.
- Analyzer could not work with earlier versions of Windows 95
- Analyzer does not work in Windows CE
- Some features could not be supported on all platforms
Analyzer Roadmap
A 3.0 final version of Analyzer should came in Spring 2008.
The 3.0 release will provide a first, affordable tool. For instance, a lot of users are pushing for getting the 3.0 final out, even if some of our objectives (in terms of functionalities) are not reached. Refinements are expected in the next minor releases.
Sunday, January 11, 2009
Broadband
Broadband in telecommunications refers to a signaling method that includes or handles a relatively wide range of frequencies, which may be divided into channels or frequency bins. Broadband is always a relative term, understood according to its context. The wider the bandwidth, the greater the information-carrying capacity. In radio, for example, a very narrow-band signal will carry Morse code; a broader band will carry speech; a still broader band is required to carry music without losing the high audio frequencies required for realistic sound reproduction. A television antenna described as "normal" may be capable of receiving a certain range of channels; one described as "broadband" will receive more channels. In data communications an analogue modem will transmit a bandwidth of 56 kilobits per seconds (kbit/s) over a telephone line; over the same telephone line a bandwidth of several megabits per second can be handled by ADSL, which is described as broadband (relative to a modem over a telephone line, although much less than can be achieved over a fiber optic circuit).
Like-Kind Exchange vs. Sales Analyzer
There are more Like - Kind Exchanges, §1031, than ever before.
Several changes to §1031 in 1991 are responsible for this increase. One
of the changes in 1991 had to do with Qualified Intermediaries. Qualified
Intermediaries, sometimes called §1031 facilitators, take a fee for turning
what would have been two sales into an exchange. Qualified Intermediaries
have actively promoted to accountants, attorneys, and brokers the benefits
of §1031.
You might be recommending a Like - Kind Exchange to your client. A
lawyer or broker might be recommending the exchange to your client. Often
§1031, are large dollar transactions, and your client is relying on you to
explain the benefits and problems with an exchange. Certainly, your client
is expecting you to do the compliance work.
This program will help you explain the cashflow cost and savings with a
§1031. The program will show the current year-after-tax cashflow savings with
the exchange compared to a sale and a purchase. It will also show what the
after tax cashflow cost might be from a reduced basis for the new asset.
This program will also help you with the compliance work. You can use it
to determine the Realized Gain or Loss, Recognized Gain, and Basis of the new
asset. It deals with the problems of loans on the properties, boot received
or paid and exchange expenses.
Friday, January 9, 2009
Brimrose NIR Analyzer
A new series of miniature near-infrared (NIR) spectrometers is said to offer a cost-effective tool for inspecting incoming
raw materials and product quality control. Compact, battery-powered Model 5030 ATOF-NIR Portable Analyzer from Brimrose Corp.
of America, Baltimore, allows laboratory tests to be performed anywhere in a plant environment. The instrument, which sells
for $28,000 (compared with $40,000 for larger units), is reportedly insensitive to ambient light, vibration, dust, and dirt.
Its design allows for quick switchover from solids to liquids, and results appear instantly on its LCD. Applications include
material identification or measurement of moisture content and active-ingredient levels. Once the instrument is calibrated,
it reportedly can be used by an inexperienced operator.
SULFUR ANALYZER
Thermo Fisher Scientific's SOLA Flare sulfur analyzers
SOLA Flare is a total sulfur analyzer system specifically designed for online measurement and monitoring of flare feed gas, giving users the ability to pinpoint in real-time when an unscheduled flare event starts and when it ends for greater regulatory compliance. Online analysis enables refineries and related facilities to minimize emissions penalities by monitoring the duration of flare events. Real-time monitoring and analysis allows users to take immediate action and make corrections without lab analysis and regulatory compliances minimizes fines associated with releasing sulfur compounds into the atmosphere. Thermo Fisher Scientific; 81 Wyman St., Waltham, MA 02454; www.thermo.com/sola
Thursday, January 8, 2009
Spectrum analyzer
A spectrum analyzer or spectral analyzer is a device used to examine the spectral composition of some electrical, acoustic, or optical waveform. It may also measure the power spectrum.
There are analog and digital spectrum analyzers:
An analog spectrum analyzer uses either a variable band-pass filter whose mid-frequency is automatically tuned (shifted, swept) through the range of frequencies of which the spectrum is to be measured or a superheterodyne receiver where the local oscillator is swept through a range of frequencies.
A digital spectrum analyzer computes the discrete Fourier transform (DFT), a mathematical process that transforms a waveform into the components of its frequency spectrum.
Some spectrum analyzers (such as Tektronix's family of "real-time spectrum analyzers") use a hybrid technique where the incoming signal is first down-converted to a lower frequency using superheterodyne techniques and then analyzed using fast fourier transformation (FFT) techniques.
Tuesday, January 6, 2009
Monitoring Centre
The system is designed for maximum flexibility, allowing solutions that meet patient needs while ensuring a friendly interface designed for ease of use by call centre physicians or nurses.
The Technology
The Telcomed system provides advanced telemedicine capabilities, including optional videoconferencing between user and caregiver. It receives medical data using a variety of communication channels, and unifies the data into an easy to understand and control information interface. The system processes, analyses and stores medical monitoring data according to a wide range of selectable criteria and offers a host of user-friendly display options at the operator station, including comparisons to past-measurements and physician video sessions.
A range of patient screens enables the physician to access and update patient information. Diagnostic, treatment, medication and monitoring data can be viewed by date, time period, medical and other criteria. Physician comments can be added, and patient responses to standard or special questions are recorded. Device inventories and other administrative functions can also be displayed.
Internet Access
In addition to being displayed at the telemedicine call centre, data, reports and notifications can be accessed and viewed on the Internet using a web browser by the user, the user's physician, clinic, emergency services or any person the user identifies as an authorized contact person. The information can also be delivered via e-mail or mail.
Data accuracy and security
Data creation, maintenance, transmission and storage within the Telcomed call centre system are protected by a comprehensive, multi-layered information security model that meets the most rigorous standards. Enhanced communication protocols ensure error-free data transmission to the system from the MedicGate™ gateway, which also stores data during power outages or phone line disruption.
Monitoring Center System Features
* Obtains medical data from a wide variety of communication channels and formats such as PSTN and ISDN telephone lines, IP, and cellular protocols.
* Analyzes medical parameters
* Voice and video conferencing capabilities
* Logs and maintains event history
* Stores current administrative user information and user medical history status
* Remotely controls home monitoring devices and gateways
* Handles medical reports
* Provides easy connection to external systems
Web Viewer
Web-Viewer enables secure Internet access to the patient’s medical data and vital signs measurement record through the medical monitoring centre.
This unique feature allows remote third-party observation by the patient’s personal physician or family for greater confidence and success in the patient’s convalescence process.
Doctor Viewer
A complete medical record is available on demand through the web for consultation by a physician or other medical personnel whom the patient has authorized.
The Doctor Viewer is "read-only" and cannot be used to modify data on the patient's file.
User Viewer
The user may add or revise any data in the medical file, store his own results of medical devices’ measurements and share this information with his personal physician.
Monday, January 5, 2009
Gas Analyzer
A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in the semiconductor industry. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to 10 − 14 Torr levels, possessing sub-ppm detectability in the absence of background interferences.
RGAs would also be used as sensitive in-situ, helium leak detectors. With vacuum systems pumped down to lower than 10 - 5Torr—checking of the integrity of the vacuum seals and the quality of the vacuum—air leaks, virtual leaks and other contaminants at low levels may be detected before a process is initiated.
Sunday, January 4, 2009
Data Recovery
 | DataRecoveryWizard Professional A file undelete and data recovery utility for Windows. It can recover files accidentally deleted, including files removed from the Recycle Bin, in a DOS window, from a network drive, from Windows Explorer with the SHIFT key held down, ... | |
 | Easy Data Recovery is a program designed for recovering deleted files from NTFS or FAT32 volumes. It can scan disc and find lost files and data blocks... | |
 | Spotmau Data Recovery Recover/transfer your important data when your Windows was crashed or the hard disk was formatted/damaged. Unformat will allow you to recover files from a partition / disk. | |
| | DOC Regenerator Solution for recovers Word documents even in most desperate situations. Indispensable tool for recovery of damaged, deleted or overwritten word documents from an existing partition as well as from corrupted, deleted partitions or reformatted disks. | |
| | XLS Regenerator Recover lost, damaged, deleted, overwritten Excel documents. It efficiently recovers a separate lost workbook from an existing partition as well as lost excel files from corrupted, deleted partitions or reformatted disks. | |
 | Pen drive data recovery software It is read-only files folders retrieval software to recover lost missing, deleted, formatted, corrupted, Data files, folders and other similar files stored in your bad crashed sticks. | |
 | FinaleMail is the email recovery software designed to recover the email database file and locates lost emails that do not have data location information associated with them. | |
 | Memory Card data recovery is easy and Non-Destructive Data restoration software utility and reliable solution to recover retrieve rescue repair restore undelete unerase | |
 | Stellar Phoenix Deleted File Recovery The most comprehensive file undelete and unerase software for Windows designed to undelete files from hard drives formatted on FAT 16, FAT 32, and NTFS & NTFS 5 file systems. | |
 | Stellar Phoenix Macintosh Data Recovery The Macintosh data recovery software, recovers data from damaged, deleted, or corrupted volumes and even from initialized Macintosh disks. | |
 | ePreserver Recovery (AOL Recovery) Quickly and easily recover deleted email messages and corrupt folders or address book entries from your AOL PFC file or Organize directory. | |
 | Quick Recovery for Database (DBF) This Advanced Database Recovery Software to recovers & repairs corrupted DBF database files. Simple and well guided steps to recover Database files. | |
| Quick Recovery For Excel Simple and Automated Excel Data Recovery/Repairing software to repair excel file that gets corrupted or damaged.. | |
| | Quick Recovery for PowerPoint Recovers and repairs corrupt Microsoft PowerPoint Presentation, Supported versions are Microsoft PowerPoint 97 and Above. | |
 | Auslogics Emergency Recovery You can Restore documents, music, photos, software programs and any other files with Emergency Recovery. You can also restore files damaged by viruses or spyware. | |
 | PHOTORECOVERY for Digital Media was developed as an easy to use application that was designed to recover images, movies, and sound files from all types of Digital Media. | |
 | DiskInternals FAT Recovery is a fully automatic utility that recovers data from damaged or formatted disks. | |
 | DiskInternals Flash Recovery is a flash memory file recovery tool that every digital camera owner should have handy. It restores all corrupted and deleted photographs even if a memory card was re-formatted. | |
 | DiskInternals NTFS Recovery is a fully automatic utility that recovers data from damaged or formatted disks. The program scans the disk first, then restores the original structure of files and folders. | |
 | Memory Card Data Recovery Software is the reliable solution to recover, retrieve, rescue, repair, restore, undelete, unerase or unformat your lost erased formatted deleted pictures images photos, audio video files and folders from mmc multimedia memory card and flash memory |
Saturday, January 3, 2009
Residual gas analyzer
A residual gas analyzer (RGA) is a small and usually rugged mass spectrometer, typically designed for process control and contamination monitoring in the semiconductor industry. Utilizing quadrupole technology, there exists two implementations, utilizing either an open ion source (OIS) or a closed ion source (CIS). RGAs may be found in high vacuum applications such as research chambers, surface science setups, accelerators, scanning microscopes, etc. RGAs are used in most cases to monitor the quality of the vacuum and easily detect minute traces of impurities in the low-pressure gas environment. These impurities can be measured down to 10 − 14 Torr levels, possessing sub-ppm detectability in the absence of background interferences.
RGAs would also be used as sensitive in-situ, helium leak detectors. With vacuum systems pumped down to lower than 10 - 5Torr—checking of the integrity of the vacuum seals and the quality of the vacuum—air leaks, virtual leaks and other contaminants at low levels may be detected before a process is initiated.
Friday, January 2, 2009
Site ContentAnalyzer - CleverStat
CleverStat is a nifty tool I've been using recently for web site content analysis. Unlike numerous online apps, CleverStat makes a copy of the site on your hard drive and analyzes the entire thing and not only individual pages
SPECTROMAXx
The new SPECTROMAXx can be configured as a bench top or floor model. With three versions to choose from, individual requirements are sure to be met.
With the new sample excitation system SPECTRO Plasma Generator, CCDs selected especially for emission spectrometry, a high-performance read-out system, a novel spark stand, innovative optical systems, and the unique ICAL logic system, the SPECTROMAXx provides analytical capabilities previously achieved only with conventional photomultiplier systems. The novel spark stand of the SPECTROMAXx is distinguished by minimal maintenance requirements and argon consumption that has been reduced by nearly half.
All of the chemical elements requiring analysis by the metal industry can be determined - including traces of carbon, phosphorus, sulfur, and nitrogen. Completely defined calibration modules are available for the relevant matrices (base metals), like Fe, Al, Cu, Ni, Co, Ti, Mg, Zn, Sn and Pb. They include the complete element range and can be adapted individually.
The SPECTROMAXx is well suited for applications like die cast or injection molding as well as for standard requirements in steel or non-ferrous foundries, also multi-matrix applications for incoming and outgoing inspection and all applications in the automotive industry.
Structural health monitoring
The process of implementing a damage detection strategy for aerospace, civil and mechanical engineering infrastructure is referred to as Structural Health Monitoring (SHM). Here damage is defined as changes to the material and/or geometric properties of these systems, including changes to the boundary conditions and system connectivity, which adversely affect the system’s performance. The SHM process involves the observation of a system over time using periodically sampled dynamic response measurements from an array of sensors, the extraction of damage-sensitive features from these measurements, and the statistical analysis of these features to determine the current state of system health. For long term SHM, the output of this process is periodically updated information regarding the ability of the structure to perform its intended function in light of the inevitable aging and degradation resulting from operational environments. After extreme events, such as earthquakes or blast loading, SHM is used for rapid condition screening and aims to provide, in near real time, reliable information regarding the integrity of the structure
IPHost Network Monitor
IPHost Network Monitor is a reliable network and server monitoring tool that allows availability and performance monitoring of mail, db and other servers, web sites and applications, various network resources and equipment using SNMP (on UNIX/Linux/Mac) and WMI (on Windows), HTTP/HTTPS, FTP, SMTP, POP3, IMAP, ODBC, PING...
IPHost Network Monitor is usable and affordable Windows software that facilitates the task of detection and elimination of failures and problems with your network and network equipment, servers, workstations and critical applications installed on them. IPHost Monitor enables you to reduce downtime (or slowdown time) because the system administrator and other concerned parties get prompt information on network resource inaccessibility or critical application performance problems. Detailed information helps to recover from the failure or remedy the performance problem quickly. With IPHost Network Monitor you can also setup actions for automatic failure recovery. Web-enabled reporting lets you monitor your network resources via a web browser to take a quick look at the state, problems and trends. IPHost Monitor does not require expensive hardware and can run at full power on a typical workstation.
To maintain the availability and performance of the network, servers and applications, to plan upgrades and maintenance, the administrator should get real time data and reports on the actual state of the enterprise’s IT infrastructure. IPHost Network Monitor provides you with a suitable and affordable solution for network, servers and applications monitoring. This tool suits both the professional administrators and all those who perform administrator’s tasks from time to time. The tool is quick and easy to set up and use. IPHost Network Monitor is efficient even when a company does not employ a full-time administrator. User interface has been developed keeping in mind that all significant information should be accessible on one screen.
Oxygen O2 Analyzer - H2S
An oxygen analyzer sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. It was developed by Robert Bosch GmbH during the late 1960s under supervision by Dr. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.
Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.
There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.
Oxygen sensor
An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. It was developed by Robert Bosch GmbH during the late 1960s under supervision by Dr. Günter Bauman. The original sensing element is made with a thimble-shaped zirconia ceramic coated on both the exhaust and reference sides with a thin layer of platinum and comes in both heated and unheated forms. The planar-style sensor entered the market in 1998 (also pioneered by Robert Bosch GmbH) and significantly reduced the mass of the ceramic sensing element as well as incorporating the heater within the ceramic structure. This resulted in a sensor that both started operating sooner and responded faster. The most common application is to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.
Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.
There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages
Operation of the probe
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of 0.2 V (200 mV) DC represents a lean mixture. That is one where the amount of oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO), produced in burning the air and fuel, into carbon dioxide (CO2). A reading of 0.8 V (800 mV) DC represents a rich mixture, one which is high in unburned fuel and low in remaining oxygen. The ideal point is 0.45 V (450 mV) DC; this is where the quantities of air and fuel are in the optimum ratio, called the stoichiometric point, and the exhaust output mainly consists of fully oxidized CO2.
The voltage produced by the sensor is so nonlinear with respect to oxygen concentration that it is impractical for the engine control unit (ECU) to measure intermediate values - it merely registers "lean" or "rich", and periodically adjusts the fuel/air mixture to keep the output of the sensor alternating between these two states. The time period chosen by the ECU to monitor the sensor and adjust the fuel/air mixture creates an inevitable delay, which makes this system less responsive than one using a linear sensor (see below). The shorter the time period, the higher the so-called "cross count"and the more responsive the system.
The zirconia sensor is of the 'narrow band' type, referring to the narrow range of fuel/air ratios to which it responds.
Oxygen Sensor Types
Today’s oxygen analyzers use one of a several types of oxygen sensors. As industrial process applications call for improved measurement accuracy and repeatability, users are also demanding analyzers that require a minimum of maintenance and calibration. To this end, users of oxygen analyzers are encouraged to evaluate the merits of a particular oxygen sensor type in context to the application for which it is intended. There is no one universal oxygen sensor type.
The synoptic review of the various gas phase oxygen sensors provided below should be used in conjunction with information gathered from manufacturers of oxygen analyzers. This combination will help to ensure the selection of the right sensor type for the application under consideration.
* Ambient Temperature Electrochemical Oxygen Senors
* Paramagnetic Oxygen Sensors
* Polarographic Oxygen Sensors
* Zirconium Oxide Oxygen Sensors
Ambient Temperature Electrochemical Oxygen Sensors
The ambient temperature electrochemical sensor, often referred to as a galvanic sensor, is typically a small, partially sealed, cylindrical device (1-1/4” diameter by 0.75” height) that contains two dissimilar electrodes immersed in an aqueous electrolyte, commonly potassium hydroxide. As oxygen molecules diffuse through a semi-permeable membrane installed on one side of the sensor, the oxygen molecules are reduced at the cathode to form a positively charge hydroxyl ion. The hydroxyl ion migrates to the sensor anode where an oxidation reaction takes place. The resultant reduction/oxidation reaction generates an electrical current proportional to the oxygen concentration in the sample gas. The current generated is both measured and conditioned with external electronics and displayed on a digital panel meter either in percent or parts per million concentrations. With the advance in mechanical designs, refinements in electrode materials, and enhanced electrolyte formulations, the galvanic oxygen sensor provides extended life over earlier versions, and are recognized for their accuracy in both the percent and traces oxygen ranges. Response times have also been improved. A major limitation of ambient temperature electrochemical sensors is their susceptibility to damage when used with samples containing acid gas species such as hydrogen sulfide, hydrogen chloride, sulfur dioxide, etc. Unless the offending gas constituent is scrubbed prior to analysis, their presence will greatly shorten the life of the sensor. The galvanic sensor is also susceptible to over pressurization. For applications where the sample pressure is > 5 psig, a pressure regulator or control valve is normally recommended.
Polarographic Oxygen Sensors
The polarographic oxygen sensor is often referred to as a Clark Cell [J. L. Clark (1822- 1898)]. In this type of sensor, both the anode (typically silver) and cathode (typically gold) are immersed in an aqueous electrolyte of potassium chloride. The electrodes are separated from the sample by a semi-permeable membrane that provides the mechanism to diffuse oxygen into the sensor. The silver anode is typically held at a potential of 0.8V (polarizing voltage) with respect to the gold cathode. Molecular oxygen is consumed electrochemically with an accompanying flow of electrical current directly proportional to the oxygen concentration based on Faraday’s law. The current output generated from the sensor is measured and amplified electronically to provide a percent oxygen measurement. One of the advantages of the polarographic oxygen sensor is that while inoperative, there is no consumption of the electrode (anode). Storage times are almost indefinite. Similar to the galvanic oxygen sensor, they are not position sensitive. Because of the unique design of the polarographic oxygen sensor, it is the sensor of choice for dissolved oxygen measurements in liquids. For gas phase oxygen measurements, the polarographic oxygen sensor is suitable for percent level oxygen measurements only. The relatively high sensor replacement frequency is another potential drawback, as is the issue of maintaining the sensor membrane and electrolyte.
A variant to the polarographic Oxygen Sensor is what some manufacturers refer to as a non-depleting coulometric sensor where two similar electrodes are immersed in an electrolyte consisting of potassium hydroxide. Typically, an external EMF of 1.3 VDC is applied across both electrodes which acts as the driving mechanism for reduction/oxidation reaction. The electrical current resulting from this reaction is directly proportional to the oxygen concentration in the sample gas. As is the case with other sensor types, the signal derived from the sensor is amplified and conditioned prior to displaying. Unlike the conventional polarographic oxygen sensor, this type of sensor can be used for both percent and trace oxygen measurements. However, unlike the zirconium oxide, one sensor cannot be used to measure both high percentage levels as well as trace concentrations of oxygen. One major advantage of this sensor type is its ability to measure parts per billion levels of oxygen. The sensors are position sensitive and replacement costs are quite expensive, in some cases, paralleling that of an entire analyzer of another sensor type. They are not recommended for applications where oxygen concentrations exceed 25%.
Zirconium Oxide Oxygen Sensors
This type of sensor is occasionally referred to as the “high temperature” electrochemical sensor and is based on the Nernst principle [W. H. Nernst (1864-1941)]. Zirconium oxide sensors use a solid state electrolyte typically fabricated from zirconium oxide stabilized with yttrium oxide. The zirconium oxide probe is plated on opposing sides with platinum which serves as the sensor electrodes. For a zirconium oxide sensor to operate properly, it must be heated to approximately 650 degrees Centigrade. At this temperature, on a molecular basis, the zirconium lattice becomes porous, allowing the movement of oxygen ions from a higher concentration of oxygen to a lower one, based on the partial pressure of oxygen. To create this partial pressure differential, one electrode is usually exposed to air (20.9% oxygen) while the other electrode is exposed to the sample gas. The movement of oxygen ions across the zirconium oxide produces a voltage between the two electrodes, the magnitude of which is based on the oxygen partial pressure differential created by the reference gas and sample gas. The zirconium oxide oxygen sensor exhibits excellent response time characteristics. Another virtue is that the same sensor can be used to measure 100% oxygen, as well as parts per billion concentrations. Due to the high temperatures of operation, the life of the sensor can be shortened by on/off operation. The coefficients of expansions associated with the materials of construction are such that the constant heating and cooling often causes “sensor fatigue”. A major limitation of zirconium oxide oxygen sensors is their unsuitability for trace oxygen measurements when reducing gases (hydrocarbons of any species, hydrogen, and carbon monoxide) are present in the sample gas. At operating temperatures of 650 degrees Centigrade, the reducing gases will react with the oxygen, consuming it prior to measurement thus producing a lower than actual oxygen reading. The magnitude of the error is proportional to the concentration of reducing gas. Zirconium oxide oxygen sensors are the “defacto standard” for in-situ combustion control applications.
Other types of oxygen measuring techniques are under development and in some cases being used for specific applications. They include, but are not limited to, luminescence polarization, opto-chemical sensors, laser gas sensors, et al. As these techniques are further developed and improved, they may represent viable alternatives to the major oxygen sensor types currently in use.
Extorr XT residual gas analyzer
The Extorr XT residual gas analyzer is a quadrupole mass spectrometer complete with a built-in Pirani gauge and Ion gauge. It is an essential measuring device which may be used in any vacuum system. The Extorr XT residual gas analyzer (RGA) models come in 100, 200 and 300 amu packages. All RGA models attach to a single 2 3/4 inch flange. Each package has automatic start-up and shut down and will constantly monitor from atmospheric pressure to ultra high vacuum. The built-in Pirani gauge and ion gauge constantly monitor total pressure and regulate and protect the RGA. These functions are seamlessly integrated into the Extorr software package.
Closed ion source
With applications requiring measurement of pressures between 10 − 4 and 10 − 3 Torr, the problem of ambient and process gases can be significantly reduced by replacing the OIS configuration with a CIS sampling system. Such an ionizer sits on top of the quadrupole mass filter and consists of a short, gas-tight tube with two openings for the entrance of electrons and exit of ions. The ions are formed close to a single extraction plate and exit the ionizer. Electrically insulative alumina rings seal the tube and the biased electrodes from the rest of the quadrupole mass assembly. The ions are produced by electron impact directly at the process pressure. Such design has been applied to gas chromatography mass spectroscopy instruments before adaption by quadrupole gas analyzers. Most commercially available CIS systems operate between 10 − 2 and 10 − 11 Torr and offer ppm level detectability over the entire mass range for process pressures between 10 − 4 and 10 − 2 Torr. The upper limit is set by reduction in mean free path for ion-neutral collisions which takes place at higher pressures, and results in the scattering of ions and reduced sensitivity.
The CIS anode may be viewed as a high conductance tube connected directly to the process chamber. The pressure in the ionization area is virtually the same as the rest of the chamber. Thus the CIS ionizer produces ions by electron impact directly at the process pressure whilst the rest of the mass analyzer is kept under high pressure. Such direct sampling provides good sensitivity and fast response times.
Open ion source
OIS is the most widely available type of RGA. Cylindrical and axially symmetrical, this kind of ionizer has been around since the early 1950s. The OIS type is usually mounted directly to the vacuum chamber, exposing the filament wire and anode wire cage to the surrounding vacuum chamber, allowing all molecules in the vacuum chamber move easily through the ion source. With a maximum operating pressure of 10 − 4 Torr and a maximum detectable partial pressure as low as 10 − 14 Torr when used in tandem with an electron multiplier.
OIS RGAs measure residual gas levels without affecting the gas composition of their vacuum environment, though there are performance limitations which include:
* Outgassing of water from the chamber, H2 from the OIS electrodes and most varieties of 300-series stainless steel used in the surrounding vacuum chamber due to the high temperatures of the hot-cathode source (> 1300°C).
* Electron Stimulated Desorption (ESD) is noted by peaks observed at 12, 16, 19 and 35 u rather than by electron-impact ionization of gaseous species, with the affects similar to outgassing effects. This is frequently counteracted by gold-plating the ionizer which in turn reduces the adsorption of many gases. Using platinum-clad molybdenum ionizers is an alternative.
Residual Gas Analyzer
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