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Reference, Questions and Help => Nuke Q&A => Instrument Q&A => Topic started by: fnbrowning on Jun 07, 2009, 02:04

Title: Unexpected Ludlum 2241 Scaler values.
Post by: fnbrowning on Jun 07, 2009, 02:04

I have a Ludlum 2241-2 manufactured in 1998. For the purposes of this discussion, I will be writing about the Detector #1 position with a 44-9 probe.
I have what appears to be an anomalous operation of the Scaler over different counting periods. 

Here is my experimental results.  I placed a SR-90 check disk against the 44-9 probe.  Readout on the Ratemeter after several minutes of observation ranges from 33.KC/m to 35.KC/m

I start with the scaler count time set to 10 seconds. The result is 5206.  Multiply by 6. (secs x 6 for 1 minute) Result is 31236 which is close to the ratemeter values.

Then I switch to scaler count time to 60 seconds. Here I conducted two tests. The results of the first test were 1915 with a small 3 in the r/h corner. This means raised to the 3rd power, correct?
The second run is 1938 with a small 3.  Obviously something is amiss with numbers like 1915000, and 1938000.

I would believe all scalers should operate similarly:  They total the counts received over a particular counting period.  If the period is 60 seconds the the results may be interpreted as Counts per Minute.

If the period is 10 seconds then indeed the results (Counts per 10 Seconds) must be multiplied by 6 in order to be expressed in Counts per Minute.  But if the period is 60 seconds the results do not need to be multiplied by anything other than 1! One would expect if the average counts over a 10 second period were about 5200 that over a period 6 times as long the average counts would be 31200

Is my scaler acting anomalously, or perhaps there limited permissible values for the counting period of the scaler?

Title: Re: Unexpected Ludlum 2241 Scaler values.
Post by: G-reg on Jun 07, 2009, 02:54

Quote from: fnbrowning on Jun 07, 2009, 02:04

Then I switch to scaler count time to 60 seconds. Here I conducted two tests. The results of the first test were 1915 with a small 3 in the r/h corner. This means raised to the 3rd power, correct?
The second run is 1938 with a small 3.  Obviously something is amiss with numbers like 1915000, and 1938000.

The Ludlum 2241 display has six digits: the four big digits which reside in the main part of the display, and the two small digits which are tucked away in the bottom-right corner of the display.  For reasons which I cannot explain, Ludlum likes to group these two sets of digits into a single 6-digit number (even though the digits are spatially separated).

If you are seeing "1915" in the four big digits, and a "3" (or "03") in the smaller digits, then the number you are looking at would be the "3" (small digit display) followed by "1915" (large digit display).  A "3" followed by "1915" would translate into "31915".  Likewise, having the large digits show "1938" in conjunction with a "3" in the small digits would correspond to "31938".  Also take note that both of these numbers corroborate well with the other source check results you've received.

On the Ludlums I've used, you can watch the counts tally up on the display in real-time during counting.  When you do your 1-minute count, keep your eyes fixed on the Ludlum's display throughout the count cycle.

• The counts displayed on the large digits should reach "9999" shortly before the 20-second point.
• Immediately after that, the counts shown on the large digits should roll over to "0000", and "1" (or "01") should appear in the small digits.
• The counts shown on the large digits should again reach "9999" at approximately the 40-second point.
• Immediately after that, the counts shown on the large digits should roll over to "0000", and the small digit display should change from "1" (or "01") to "2" (or "02").
• And finally, shortly before counting terminates the large digits should roll past "9999" one last time, and the small digits should change from "2" to "3".  Based on your earlier results, the large digits should come to a stop around 1900-1950 when the one minute counting cycle completes

Title: Re: Unexpected Ludlum 2241 Scaler values.
Post by: fnbrowning on Jun 07, 2009, 11:30

G-reg;

I confess I thought that I had read completely through the on line manual. I see now I missed the part where it said:

>>"The scaler display uses the 2 digits in the lower right hand corner for the 2 most significant digits of the 6-digit readout."<<

Your post made sense and clued me in with what to look for. Reading is fundamental.  :-[

Cheers!