Industrial ppm CO measurementsWritten by Scott Cowe of Dover Gas Technologies
Continued from page 1
higher temperature coefficient, this leads to zero instability making it unsuitable for our task. Carbon and chemical filters are often attached to face of sensor or added in sample stream to diminish effects of cross interference to many of commonly encountered such as H2S, SO2, NO x, etc.. This filter, itís efficiency and life span can be an important consideration when measuring CO in 0-50ppm range. In a number of applications background levels of Hydrogen given off by nearby processes have been found to cause major problems with accurate low level carbon monoxide measurements and alarms. While it is possible for hydrogen levels to cause safety concerns that should be reported, limit is magnitudes higher than what causes CO alarms to trigger on most instruments. A hydrogen level of as little as 60ppm can trip CO alarms of many analyzers. The lower explosive limit (lel)for hydrogen is 4%, ten percent of that l.e.l. would be 4000ppm, so we see that 60ppm is insignificant to personnel safety but remains problematic to carbon monoxide measurement. This cross interference can not be easily overcome with chemical filters and therefore required a different approach. It has been found that by measuring hydrogen separately and using that signal in conjunction with mixed CO/H2 signal majority of interference can be nulled out, again manufactures deal with this differently with varying results. The use of two separate sensors can create a compensation lag time and there may be temperature coefficient differences between sensors, either of which will cause errors in readings and provide false alarms. Similar temperature problems can be found with units that use a single sensor but do electronic nulling and temperature compensation remote of sensor itself.
There are sensors now available that have separate electrodes for H2 and CO/H2 signals with nulling and temperature compensation circuit attached directly to rear of sensor itself. The output of this surface mount board is in millivolt range making it less susceptible to interference and change from wiring, connectors and temperature effects. Each sensor and attached PCB come completely pre-calibrated for H2 cross interference and relative CO output. Only a single calibration gas is required over life of sensor (2 years) with no need for re calibration of hydrogen signal nulling found in any of units put into service. In addition, internal chemical filter provides excellent reduction of cross interference due to other common gasses found. This customer replaceable sensor has proven itself over time to provide consistently accurate results in demanding applications against competitors instruments.
Dover Gas Technologies Inc. www.dovergas.com incorporates such a sensor, we believe it best suits needs addressed above and use it in many of our portable, transmitter, and monitor products for low level ppm CO measurement.
President and operations manager of Dover Gas since 1991 with 8 years of prior experience in the gas analysis field.
Installing Nessus 2.0 on SuSE 9.0 Pro with KDE 3.1Written by Lew Newlin
Continued from page 1
- Click "Local Network"
- Change location to "/"
- Right click and Create New directory titled "nessus-installer", close window
- Using browser go to http://www.nessus.org/nessus_2_0.html
- From "The easy and less dangerous way" section download "nessus-installer.sh" file saving to "nessus-installer" directory.
- Click "Konsole" on task bar and change directories to "nessus-installer"
- Type "sh nessus-installer.sh"
- Accept defaults by pressing (During compiling process you may receive warning messages for "nessus_popen", "insert_nasl_func", and "extra tokens". These are warning messages and compiling process should complete successfully.)
- When compiling process is complete you will be prompted to press to quit.
Nessus Server Setup
- Type "nessus-mkcert" to make a server certificate
- Accept default for "CA certificate life"
- Accept default for "Server certificate life"
- Enter your 2 letter country code
- Enter your state or province code
- Enter your location
- Enter your organization name
- Certificate process completed message
- Type "nessus-adduser" to create a user account
- Enter login name
- Accept default for authentication
- Enter password
- Press ctrl-D to end user creation process
- "Is that ok?" message
- Type "nessusd -D" to start Nessus server service (It may take several seconds for Nessus to finish initializing. The command prompt will return once Nessus daemon is started).
If you wish to have Nessus Server daemon automatically started when system is booted, edit "etc/init.d/boot.local" file and append "nessusd -D".
- Type "nessus"
- Enter login
- Enter password
- Click "Log in" button
- "SSL Setup" window will appear, click
- "Nessus" windows asking to accept this certificate, click
- "Warning" message about plugins crashing remote systems will appear, click
- Close "Konsole" window
- Click "Start Applications" on task bar and select "Utilities", "Time", then "KAlarm"
- In KAlarm window click "Actions", then New
- Check "Command" and enter "nessus-update-plugins" as command line
- Check "Any time" check box
- Check "Recur" for Repetition, then select "Recurrence" Tab
- Enter "01:00" for "Recurr every" field
- Select button, then
- Close "Kalarm" window (Kalarm by default is automatically stated upon boot.)
KDE provides built-in firewall protection. Vulnerability scanners such as Nessus do not normally function well with software firewalls in place. To remove firewall:
- Click "Control Center" on task bar
- Click "YaST2 modules"
- Click "Security and Users"
- Click "Firewall"
- Check "Stop Firewall and Remove from Boot Process"
- "Firewall configuration - deactivate firewall", click
- "The firewall is now turned off"
Uninstall executable: /usr/local/sbin/uninstall-nessus
Configuration file: /usr/local/etc/nessus/nessusd.conf
Certificate Authority: /usr/local/com/nessus/CA/cacert.pem
Certificate Authority - Private: /usr/local/var/nessus/CA/cakey.pem
Nessus Server Certificate file: /usr/local/com/nessus/CA/servercert.pem
Nessus Server - Private Key file: /usr/local/var/nessus/CA/serverkey.pem
Nessus uses port 1241 to communicate
You now have a fully functioning Nessus server daemon and client installed on SuSE using KDE desktop environment. Kalarm is setup to automatically update Nessus plugins once per hour to insure you have latest vulnerability tests. Nessus is now fully operational to help with your security needs.
Lew Newlin is CTO of Information Solutions, Inc. that operates SiteRecon.com. SiteRecon specializes in security, email monitoring, and web site monitoring for Internet service providers and businesses.