7
Taking an average allows you to detect low-level contamination or differences in
background radiation due to altitude or soil mineral content. For example, if one
10 minute average is one count higher than another 10 minute average, the increase
may be due to normal variation. But over 12 hours, a one-count increase over the
12 hour background average is statistically significant.
To take a timed count, follow these steps:
1.
With the Digital Radiation Monitor operating, set the Mode switch to
Total
.
The display shows
SET
, the hourglass, and the most recent timing period used.
The first time you use the timer, the setting is 00:01, which means one minute.
2.
Use the + and – buttons to set the timing period. The timed period can be for 1
to 10 minutes in one-minute increments, for 10 to 120 minutes in ten-minute
increments, or for 2 to 40 hours in one-hour increments.
3.
Press the Set
button. The Digital Radiation Monitor starts totaling the counts it
registers, and the numeric display is updated each time a count is registered. The
hourglass indicator flashes during the timed period.
During the counting period, if you want to see how many minutes remain, press
the Set button. The display counts down from the time setting in hours and
minutes to zero. For example, if the display shows 00:21, 21 minutes remain.
4.
At the end of the timed period, the Digital Radiation Monitor beeps three times,
and repeats the beeping several times. The number displayed is the total count.
5.
To find the average dose rate for the timed period, divide the total by the
number of minutes.
The average count is in counts per minute. To convert to mR/hr for Cesium-137,
divide by 1000.
6.
Move the Mode switch to one of the dose rate modes to return to normal
operation.
If you move the Mode switch to one of the dose rate modes while the Digital
Radiation Monitor is taking a timed count, the timed count will stop.
Operating Ranges and Response Times
The following table shows the radiation levels the Digital Radiation Monitor
measures in each mode and how they are displayed. In some modes, when radiation
levels increase over certain preset levels, the Digital Radiation Monitor uses
autoranging, automatically changing to the X1000 scale. Whenever
X1000
is shown,
multiply the displayed reading by 1000 to determine the radiation level.
Mode Regular
Range
X1000
Range
mR/hr 0.001–110
NA
μ
Sv/hr 0.01–1100
NA
CPM 0–9999
10,000–350,000 (displayed as
10.00–350, with X1000 indicator)
CPS 0–3500
NA
Total/Timer 0–9999
10,000–9,999,000 (displayed as
10.00–9999, with X1000 indicator)
8
Maximum level.
When the maximum level for the current mode is reached, the
Digital Radiation Monitor beeps for three seconds, pauses for three seconds, and
repeats that pattern. The numeric display flashes. The beeping pattern and the
flashing continue until the level decreases or the Digital Radiation Monitor is turned
off.
Display update and response time.
In Total mode, the numeric display is updated
each second. In the dose rate modes, the numeric display is updated every three
seconds. When the radiation level is less than 1,000 CPM, the reading in any of the
dose rate modes is based on the radiation detected in the immediately previous
minute. In order to give a quicker response to changes, when the radiation level
exceeds 1,000 CPM, the reading is based on the previous 3 seconds, as shown in the
following table. This automatic change in response time is called auto averaging.
Radiation Level
Basis for Reading
<1000 CPM or 1 mR/hr
1 minute
>1000 CPM or 1 mR/hr
3 seconds
Note:
You can set the response time to 3 seconds at all radiation levels using the
Utility Menu; see “The Utility Menu” in this chapter.
The Utility Menu
The Utility Menu allows you to change the default settings for several operating
parameters. A new setting remains in effect until changed again through the Utility
Menu.
•
To activate the Utility Menu, hold down the + button on the end panel while you
turn on the Digital Radiation Monitor; the word
MENU
will appear at the
bottom right of the numeric display. When you release the + button, a 1
(indicating menu option 1) will appear above
MENU
.
•
Scroll through the menu by pushing the + or – buttons.
•
To select an option, push the Set button. Use the + and – buttons to toggle
between choices, and press the Set button again to enter the chosen value.
•
To exit the Utility Menu at any time, select option 0. The Digital Radiation
Monitor continues with the normal start-up routine.
The options are:
0 Resume normal operation.
1 Auto
Averaging.
on
(the default) selects Auto averaging;
oFF
selects 3-second
(fast response) averaging at all radiation levels.
2 Units of measurement. CPM mR/hr
selects counts per minute and
milliroentgens per hour;
CPS
μ
Sv/hr
selects counts per second and
microsieverts per hour.
