Logic Analyzer

A logic analyzer is an electronic instrument that displays signals in a digital circuit that are too fast to be observed and presents it to a user so that the user can more easily check correct operation of the digital system. They are typically used for capturing data in systems that have too many channels to be examined with an oscilloscope. Software running on the logic analyzer can convert the captured data into timing diagrams, protocol decodes, state machine traces, assembly language, or correlate assembly with source-level software.

Presently there are three distinct categories of logic analyzers available on the market:

* The first is mainframes, which consist of a chassis containing the display, controls, control computer, and multiple slots into which the actual data capturing hardware is installed.
* The second category is standalone units which integrate everything into a single package, with options installed at the factory.
* The third category is pc based logic analyzers. The hardware connects to a computer through a USB or LPT connection and then relays the captured signals to the software on the computer. These instruments are less expensive than either mainframes or standalone units although they lack the sophisticated functionality.

A logic analyzer can trigger on a complicated sequence of digital events, and then capture a large amount of digital data from the system under test (SUT). The best logic analyzers behave like software debuggers by showing the flow of the computer program and decoding protocols to show messages and violations.

When logic analyzers first came into use, it was common to attach several hundred "clips" to a digital system. Later, specialized connectors came into use. The evolution of logic analyzer probe has led to a common footprint that multiple vendors support, which provides added freedom to end users. Introduced in April, 2002, connectorless technology (identified by several vendor specific trade names: Compression Probing; Soft Touch; D-Max) has become popular. These probes provide a durable, reliable mechanical and electrical connection between the probe and the circuit board with less than 0.5pF to 0.7 pF loading per signal.

Once the probes are connected, the user programs the analyzer with the names of each signal, and can group several signals into groups for easier manipulation. Next, a capture mode is chosen, either timing mode, where the input signals are sampled at regular intervals based on an internal or external clock source, or state mode, where one or more of the signals are defined as "clocks," and data is taken on the rising or falling edges of these clocks, optionally using other signals to qualify these clocks.

After the mode is chosen, a trigger condition must be set. A trigger condition can range from simple (such as triggering on a rising or falling edge of a single signal), to the very complex (such as configuring the analyzer to decode the higher levels of the TCP/IP stack and triggering on a certain HTTP packet).

At this point, the user sets the analyzer to "run" mode, either triggering once, or repeatedly triggering.

Once the data is captured, it can be displayed several ways, from the simple (showing waveforms or state listings) to the complex (showing decoded Ethernet protocol traffic). The analyzer can also operate in a "compare" mode, where it compares each captured data set to a previously recorded data set, and stopping triggering when this data set is either matched or not. This is useful for long-term empirical testing. Recent analyzers can even be set to email a copy of the test data to the engineer on a successful trigger.

Many digital designs, including those of ICs, are simulated to detect defects before the unit is constructed. The simulation usually provides logic analysis displays. Often, complex discrete logic is verified by simulating inputs and testing outputs using boundary scan. Logic analyzers can uncover hardware defects that are not found in simulation. These problems are typically too difficult to model in simulation, or too time consuming to simulate and often cross multiple clock domains.

Field-programmable gate arrays have become a common measurement point for logic analyzers.

Today, the most common method of data capture for logic analyzers is through a probe. A logic analyzer can measure anything electronic if it has the proper probe connected. Mostly logic analyzer measure data buses. The probes try to tap into the electronic signals being passed through a data bus or wire.

Tail Gas Analyzer

The analyzer
The analyzer’s design8 adheres to the principle of no moving parts and no sample lines in sulfur recovery applications. The same diode array analyzer is utilized here, but an in-situ probe is used in place of the typical flow cell.
Demister “cold finger” Probe
A patent-pending demister (“cold finger”) probe is used for in-situ measurements. The setup requires very low maintenance, benefiting from the innovative in-situ probe. The probe is designed to draw a continuous sample into its body, and remove the sulfur vapor. This is done by a “cold finger” which condenses the sulfur out of the gas in a controlled manner, and an aspirator, which draws the sample into the sample chamber, and returns it to the process line.
The probe is constructed from three concentric tubes. The outer tube, called the “sample chamber”, is 1.5" in diameter. This tube passes down through a ball valve into the process line, where its angled tip helps draw the tail gas into the chamber. The cold finger tube located inside the sample chamber is kept much cooler than the process gas. This causes most of the sulfur to condense and drip back into the process, creating a sample stream that is free of sulfur vapor. Cooled air is constantly fed to the bottom of the cold finger through a smaller internal tube and is exhausted out the opposite side. These three tubes are welded to the first section of the probe’s head, a 1” thick disk made of 316 stainless steel. Above this is a second disk, which contains an air-driven aspirator. This provides a vacuum, which draws the process gas into the sample chamber, past the cold finger, and up through an integrated flow cell at the top of the probe head. The aspirator then pulls the sample down through a waste tube, where it is exhausted back into the process.
All air/gas connections in the head are ¼” Swagelok tube fittings. These accommodate the aspirator air in, cold finger air in and out, and calibration gas in. The integrated flow cell has fiber optic connections on each side. The system periodically washes and zeros itself. Calibration gases can be introduced into the probe at any time for data verifications, although recalibration or spanning is not required, since it is a solid-state analyzer.


Tail gas analyzer - UV absorbance spectra
The concentrations of up to five components are measured: H2S and SO2 for process control, COS and CS2 for catalyst efficiency, and sulfur vapor for signal compensation. Each one of these components has unique UV absorbance spectra. Figures 3 and 7 show the absorbance spectra of H2S and SO2 at different concentration levels. Figure 8 shows the total signal of a mix of 1% H2S and 1% SO2 and the individual signals. The absorbance spectra of the individual components are superimposed to give the total absorbance spectrum of the process sample (see Figure 9). To de-convolute the signals of each of the components, a full-spectrum, multi-component algorithm is used

Gas Analyzer

The Thermal and Evolved Gas Analyzer (TEGA) is a scientific instrument aboard the Phoenix spacecraft. TEGA's design is based on experience gained from the failed Mars Polar Lander. Soil samples taken from the Martian surface by the robot arm are eventually delivered to the TEGA, where they are heated in an oven to about 1,000ºC. This heat causes the volatile compounds to be given off as gases which are sent to a mass spectrometer for analysis. This spectrometer is adjusted to measure particularly the isotope ratios for hydrogen, oxygen, carbon, nitrogen, and heavier gases. Detection values as low as 10 parts per billion. The Phoenix TEGA has 8 ovens, which are enough for 8 samples.

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.

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.

How much should I spend on a Protocol Analyzer?

This is the crux of the problem. Will an expensive analyzer deliver more than a cheaper one? Will I get more value from a higher cost product? My advice is to consider it very carefully before you decide. You can spend a significant amount of money on an analyzer, but you may not have to.

Proprietary solutions vary enormously in price and functionality. Although most make use of open formats (or at least allow data to be exchanged between different systems) you should check carefully that you are not tied into proprietary formats. It is very inconvenient to capture packets and then to have to mess around converting from one format to another if you need to share the information. Open Source analysis products have the huge advantage of being completely free, use open formats, and often provide as much functionality as proprietary solutions.

Decide on the features that you really need. If, in addition to protocol analysis, trending and performance measurements are very important to you a proprietary solution may be the best, since integration of the two functions is often very good. Again open source alternatives do exist so you could go for both a performance monitor and a protocol analyzer.

If technical support and training are important these are generally better provided for by proprietary solutions, though normally at additional cost.

If full wire speed packet capture is a requirement then you may have to consider a hardware solution, but these are extremely expensive and are normally only justified in special cases.

It is worth trying as many analyzers as possible to see which suits you best. For the types of problems described above the really important feature is the sophistication of the filtering mechanism. Again look carefully at what is being offered.

Email Problems

Email systems typically use standard port numbers, 25 for SMTP, 143 for IMAP, 110 for POP3. Setting filters for these ports will usually help to discover the cause of problems with email.
Virus Detection and Control
Anti virus software manufacturers offer updates services. Armed with the information on new threats it is often possible to build suitable filters to detect viruses. For example many analyzers allow you to specify a text pattern so a virus contained in a message containing a known text string could be detected. Analysis of the capture will show the source and destination of the packets.
Firewalls
Firewalls need to be checked for outgoing and incoming traffic. You will have to define a set of filters for traffic in both directions. Should the firewall begin to let unauthorized traffic through you need to be able to detect it.

What to Look for? Unexpected Traffic

The obvious thing to do is monitor the network for unexpected traffic. Most network managers know the types of application that they expect to see and can point out anything unusual. If anything unexpected is spotted then a capture of some of the traffic is usually sufficient to pinpoint the machines involved.
Unnecessary Traffic
It is common for machines to be set by default to run protocols that may not be required. Many printers broadcast using Novell's IPX protocol. Fine if you are using NetWare, but not always necessary. It's good housekeeping to remove any protocols that you do not need. You may be concerned about how your users are using the available bandwidth. A good analyzer will allow you to filter specific types of traffic so that you can keep an eye on any traffic that may cause you a problem.
Unauthorized Program Use
Likewise it is useful to check the specific port numbers for services on your Servers. They may be offering services that you do not need, or unauthorized users may be accessing them. Most common services operate on defined port numbers, a packet capture on a Server will soon reveal what services are running. You can disable any services that you do not need. This has two benefits, one, it avoids unnecessary traffic on the network, and two it means that no unauthorized user can take advantage of that service. If anyone is using a service a packet capture will show you the address. Most analyzers allow filtering on specified port numbers so it is possible to monitor continuously for specified port numbers.