CDV Counter User's Guide

Contents

WHAT IS IT?

CDV Counter displays total counts, Counts Per Minute (CPM), and milliRoentgens/hour (mR/hr) integrated over a user-selectable time period.

By repeating measurements CDV Counter can graph activity over time.

Measurements can be displayed over the Internet in a Web Browser.

Cosmic rays can be detected by feeding 2 CDV700's into both audio channels.
 

REQUIREMENTS

• Windows95 or later PC
• Soundcard, 8 bit monaural 11kHz capable (ie, any)
• Something that generates clicks, cabled to the soundcard's line input

INSTALLATION

1. Create a new directory
2. Unzip all these files there
3. Run cdvcounter.exe

cjpeg.exe            -convert bitmaps to jpeg files
help.html            -this help file
*.GIFs               -screenshots for the Help file
cdvcounter.ini    -sample configuration file
*.txt                   -misc. text files

UNINSTALLATION

1. Delete the directory you created

USAGE

• Connect the phono output of a CDV 700 to a PC soundcard's line input.
• Adjust the gain on your sound card.  Caution, the CDV will be loud!  You can mute this using your soundcard's mixer.
• Run CDVCounter and press the CDVCounter's "Start" button.
• You can abort a series of measurements with the "Cancel" button.

SETTINGS

Note that the counts recorded from a given audio stream will vary with the pulse-detection threshold.  Thus you should keep the threshold constant so that you can compare your measurements.  A threshold of 100 works well at low count rates.  See below on Calibration.  You must also keep the soundcard's line-input mixer gain constant if you want to compare measurements.

You can specify a number of times to repeat a measurement, e.g., for measuring decay curves over time.  After more than one point has been measured, you can graph the resulting values.  Each graph point represents the CPM rate for one interval of the specified amount of sampling time.
 
 

GRAPHING

If you have made repeated measurements, you can raise a resizable graph of CPM over time.  Their current average is also displayed. You can change the type of graph from the Options dialog.  If the graphing window is narrower than the number of data points, the data are averaged.

To save the graph, use Windows' Control + PrintScreen keyboard combination to capture the screen to the Clipboard, then paste into any application (eg Paint).

One graph style

Another graph style

Yet another

If you have told CDVCounter to sample "forever", this graph will show a finite number of previous samples.  You can adjust the number of samples in the "Scroll Width" Option.
 
 

OPTIONS

See the Version History for extra details on these features.

Saving Data

• The "Save As..." button lets you save your CPM measurements as a text file.
• The "Add Notes..." button lets you prepend text to the CPM file before you save the data.
• The "Insert Commas" checkbox lets you format the counts in a format suitable for spreadsheets.  You might have to remove any notes you have added to obtain a pure numbers and commas file.
• The "Text Graph" checkbox includes a text-graph of the activity in the data file.

Other Options

• Run a built-in web server on a designated port
• Remove periodic "timing" ticks from some inputs
• Count pulses in a pre-recorded WAV file.  The file must have been recorded with the indicated parameters.

Graphing

• Checkboxes let you change graphing styles and a text field lets you set the title of the graph window.
• The "Write JPG" checkbox causes the graphing window to update "cdvcounter.jpg" even if the web server is not running.
• The "Scroll Width" field is used when sampling "forever".  Scroll Width is the number of most recent samples to graph.

 

Autostart

• You can tell CDVCounter to start sampling when run.  The next time you start CDVCounter it will start sampling immediately.  This is useful for turn-key demos, e.g., in libraries.

Coincidence Detection

• You can tell CDVCounter to listen to both Left and Right audio channels and count only simultaneous pulses.  This is useful for cosmic ray detection.

CALIBRATION

CDV Counter samples the audio input at 11Khz, monoaural, 8 bits per sample.  It detects pulses when it sees sufficiently steep rising edges.  The threshold setting is the difference between successive samples which counts as a pulse.  We don't need sophisticated algorithms to detect monster CDV 700 pulses.

Again, the program's threshold settings and soundcard mixer's line-input gain must be left alone if you plan to compare CDV Counter measurements.  E.g., background vs. some source.  Both the threshold and gain affect the number of pulses counted.

Ok, how should we set these parameters?   Maybe the CDVCounter program output should agree with the analog meter?  And/or with other instruments?

The CDV Counter threshold can be adjusted to give counts that agree with the '700's analog measurement or other calibration.
Its up to you to check that your readings are consistent with what your instrument(s) otherwise report.  For instance, a fellow hobbyist reports that CDV Counter is consistently .05 mR/hr below the instrument supplying pulses (a Belvar), using the default CDV Counter threshold of 100.  Another reports that CDVCounter works with a Digilert with threshold 125.  Another reports seeing accurate results with counts to 100K CPM.

This project has caused me to think about why and how you come to trust instruments and the measurements they make.  And repeatability, transferability, etc.
A good scientist validates his tools as well as his techniques.  Skepticism is a good thing.  Damn, this sounds like an argument for the NIST (aka NBS) folks!

Thoughts on Calibration

Absolute Comparison With A Steady CDV700 Analog Meter

In fact, it seems high rates need high thresholds.  See this document for my experimental notes on this.
For best absolute agreement with the 700's analog needle, larger fluxes needs larger threshold.  For instance, when the CDV700 saw 9 mR/hr the CDVCounter program agreed best when the threshold=145 vs. threshold=110 at 1 mR/hr.  I use the default of threshold=100 for low fluxes, where the program is the most useful.

I have yet to do comparisons between my CDV 700 (with or without the CDV Counter program) against other GCs.  Different GCs will usually give different readings due to geometry and tube-sensitivity anyway.
 
 

Using Distance To Generate Known Radiation Fields

Using Sheilding To Generate Known Radiation Fields

LIMITS

Measurement Dead Time

After an ionization, a Geiger-Muller tube will not respond.  This "dead time" causes the response to be significantly sub-linear at high count rates.  (It also happens at low count rates, but infrequently.) This is normal and a property of the tube and its voltage.

The way that interaction frequency varies with energy also affects measurements.  GM tubes are more sensitive to lower energy gammas, since high energy gammas don't interact with matter as much.

I haven't measured the linearity of the CDV Counter program with a '700.  Or the linearity of the '700 by itself.

I found that for best agreement with the analog meter, larger fluxes need higher thresholds.
 
 

Memory Buffering

Audio samples are stored in a RAM memory buffer before processing.  This buffer occupies 11 KBytes of memory per second sampled.  So if you want to measure for a day, you're better off sampling for a few minutes and having CDV Counter automatically repeat the measurement.  Their average will be the same.
 

Tested

EXPERIMENTS

With this tool and a CDV 700, I've been able to measure betas from K-40 in 3 oz. of KCl (salt substitute), which is only 50% greater than background, and basically impossible with a CDV 700 by itself.

I've also measured 1uCi Am-241 ~60keV gammas at 3 x background.  With the beta shield open it records 15 x background.  Background is 0.01 mR/hr here, beta shield open.

Others have used a CDV 700 & this tool to measure activity of granite tabletops.

I've also been able to graph the decay of Radon daughters.  One sees an apparent half-life of just under an hour, from beta emitters Pb-214 (27min) and Bi-214 (20min).

Others have used this tool with a Belvar GC, and it was thought that CDVCounter needed to remove periodic timing ticks from the input. It turned out that the timing ticks aren't detected with the default threshold because they are lower amplitude and less steeply rising.

John Boyle reports using this with a homebrew cosmic ray muon detector!  (He uses 2 detectors and an AND gate correlator.)  This may run in a library.  The "autostart" option was added to make this a "one-click" tool for the librarian.
 
 

CABLING

I was able to use a male "PL-259" RF plug, attached to some coax cable, by snipping off the long center conductor so that it resembled the little nub of the original.  A little bit of aluminium foil can help maintain the central conductor conductivity.

The original is an "Amphenol Microphone Connector 75-MCIF".

Reportedly this is still made as a "Switchcraft 2501" series, "Mouser Electronics part no. 502-2501F."

You can also find a kludge at http://www.ans.org/pi/teachers/reactions/2001-04-02.html which involves modifying the plastic cover for the Phone plug to make your CDV-to-soundcard cable.
 
 

MISC

Make sure that your PC doesn't try to go to sleep (power conservation) if you leave it alone while you're recording.

You can "mute" the line-input so that you can still play music on your PC while taking measurements.  Without listening to the clicks.

TERMS & ACKNOWLEDGEMENTS

Comments to: revtkatt @ yahoo.com
If you find this useful or have suggestions I'd like to hear about it.

Thanks to the Yahoo CDV 700 Club group.
 
 

Version History, New Features

NEW FOR V 0.3  Web Server

Your Geiger Counter can be a webserver!  NOTE: This now includes image of activity graph!

In the CDV Counter Options window, you can start a web server that displays your counter's activity.

You can choose the TCP port to run the web server on.  This avoids conflicts and ISP blocks.

If you have a static IP address (some Cable, DSL users) your CDV 700 can be seen world-wide with any browser.

Pick a Port

You can test this by opening http://127.0.0.1:700
"127.0.0.1" means "the local machine".  The ":700" is part of a URL; it defaults to 80.  You should get a page generated by the CDV Counter's web server.

If you're using port 80 your URL could be simply http://127.0.0.1 because 80 is the default.

If you have a Cable or DSL modem and know your IP address (run "winipcfg") is 12.34.56.78 then the world can use http://12.34.56.78:700  to see your results.  Or again, if using port 80, simply use http://12.34.56.78 These world-wide (vs. local) IP addresses won't work if you have a firewall blocking incoming connections; See below if you run one.
 
 

Firewalls

If you run a firewall, poke a hole in it, otherwise it will block incoming connections to CDVCounter.  In your firewall's configuration, find something called "forwarding".  Allow TCP incoming connections for the port number that you chose (e.g., 700).

If you have more than 1 PC in your LAN, you may have to tell the firewall which of your LAN machines to forward a request on that port.  Your local machine addresses will probably be something like 192.168.1.100.

Try a repeated short-duration measurement, graph it, and watch the webpage get updated.
 

NEW For 0.4

NEW for 0.5

NEW for 0.52

New for 0.6

Added:

• "Forever" Button -repeating 999,999,999 times means "forever" now.   This changes the graphing style to scrolling, instead of fitting all the data into the graphing window.
• "Scrolling width" is adjustable.  Scrolling width is number of points displayed in "forever" mode.  Saved in INI.
• Editable Graph Window title.  Saved in INI.
• Option to start sampling automatically when program is started.  This also opens the Graphing window  automatically.     Saved in INI.

To make this a "one-click" tool for a library:

1. In the Options window, Edit the Graph Window Text .
2. In Options, select Autostart.  (Note: This will open the Graphing window automatically.)
3. In the main window, Press the Forever button.
4. Exit the tool to save your settings.

      To Start Automatically Upon Windows Login, Create a shortcut in the Taskbar's Programs | Startup menu.

     You might also create a desktop icon so that if the program is stopped, you can run it again easily.
 

0.62 HTMLized This Help file.  Added figures.

0.70 Web server can display dynamic activity graph

If the Web server is running, and the Graphing window is open, then the Graph is written as a Windows Bitmap .BMP file ("cdvcounter.bmp") after each new sample.  And the Web server will display the Graph in its self-refreshing web page.  (Works with IE 4.0) Note that sample times that are too brief  will keep the CDVCounter PC and remote browsers quite busy; in part because Bitmaps are inefficient.  Note that the graph displayed on the web page is the same size as the local PC's graph.

If you want only to look at the graph, its URL would be http://127.0.0.1:700/cdvcounter.bmp

CDVCounter's Web Page viewed with a Web Browser
 
 

0.71 JPEG generated from BMP and used in web page instead of BMP

0.72 A crash-causing memory leak was fixed, also a fix when changing the scrolling width.

Used "cjpeg.exe" utility to create JPEG from BMP in web page; this saves bandwidth.
 

0.73 Forgot to include cjpeg in 0.72

0.74 Improved generation of JPEG from BMP.

0.76 Added option to write JPG File whenever Graph Window is updated.  When built-in Webserver not used.

If you check this box in the Options dialog, a new JPG file is written after every measurement.  (Without checking the box, JPGs are written only if the Webserver needs them.)

Recall that CDVCounter writes cdvcounter.jpg to the same directory containing the CDVCounter.exe program.
 

0.77 Added "fill under the graph" display option

0.80 Added Coincidence Detection for Cosmic Ray logging

A "Coincidence Detect" checkbox was added to the Options dialog.  Enabling Coincidence Detection causes CDVCounter to look in both Left and Right audio channels looking for pulses.  A pulse detected in both channels simultaneously counts as a detection event.

Notes:

• "Simultaneous" depends on the audio sampling rate, which is currently fixed.
• You will always occasionally have false alarms no matter how small your simultaneity window.  Do the math :-)
• Pulses are detected in both audio channels with the same threshold, and there is typically no way to adjust left vs. right audio gain.  (At least on my computer.)  However, given that the audio clicks are typically huge, this should be little problem since they'll always be detected.

Thanks to k0ff for suggesting this.  As usual, I'd like to hear about anyone's experiences with this feature.

[Note added May 2004: Justin of the CDV700Club has been testing this and it seems to work.]
 

.81 Added 95% confidence interval to log

The interval is from C-1.96*sqrt(C) to C+1.96*sqrt(C) where C is the counts and 1.96 comes from the Gaussian distribution.
Also fixed an extra character at the end of the date-string that was showing up as an unprintable char.
 
 

.82 Fixed a bug involving miscomputed running averages.

.83 Immediately clear averages when zeroing them.