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CD V-750 and Dosimeters
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CD V-750 Dosimeter Charger and Dosimeters
First, a brief description of what a dosimeter does...
The electrostatic dosimeter is a pen-size scientific instrument with an eyepiece
you look into at the top of dosimeter and a charging contact at the bottom.
Inside the device is a microscopic scale with a hairline indicator. This
shows the amount of radiation absorbed by the device since the last time
it was reset to zero. The dosimeter is reset by charging it with electricity
using with a dosimeter charger (pictured at right with dosimeter on charging
contact). This device fills the inner chamber of the dosimeter tube with
a high voltage charge. By looking through the eyepiece while this is being
done, the user can manipulate the charger knob to reset the hairline indicator
on the radiation scale inside the dosimeter to the "0" point.
This sets the dosimeter to zero and readies it for use.
The user then carries the dosimeter on their person (hence the clip on each
dosimeter, to hold it in a pocket or on clothing)
while he works near radiation. As radiation passes through the dosimeter
(and the wearer!) it discharges the dosimeter and the hairline indicator
on the scale will move up from 0, which thus records the total dose of radiation
that passed through the dosimeter (and again, through the wearer!) since
it was reset.
Any time the wearer wants to check how much radiation he has received, he
can take the dosimeter out, point it towards a light source, and look through
the eyepiece at the microscopic scale inside. If any radiation was received,
the hairline indicator will have moved upscale from 0 and will show the
amount of radiation received by the wearer.
Standard Civil Defense Dosimeters
The CD V-138, CD V-730, CD V-740 and CD V-742 (from left to right in photo)
are the standard dosimeters used by Civil Defense. The CD V-742 is the most
commonly found dosimeter due to there being over 3 million of these produced.
The CD V-138 is a low-range 200 millitoentgen scale range dosimeter used
for training. The CD V-730s and CD V-740s were early dosimeters that were
superseded by the CD V-742. There were approximately 160,000 of each of
New Version CD V-138 And CD V-730 Dosimeters By Arrowtech Inc.
New CD V-138 Dosimeter
Range 0-200 Milliroentgens
Reads Gamma Radiation
Low range dosimeter.
New CD V-730 Dosimeter
Range 0-20 Roentgens
Reads Gamma Radiation
Here are some new versions of the CD V-138 and CD V-730 dosimeters manufactured by Arrowtech Inc. I didn't know that these were
in production until I got some CD V-777-1 kits that had a few of these new style dosimeters in them. I searched Arrowtech and
found their company site still selling them.
CD V-750 Dosimeter Chargers
Here is a sampling of some of the chargers I have in my collection. Top
row left to right: Bendix 643 (CD V-750 Model 1), Jordan CD V-750 Model
2, Universal Atomics CD V-750 Model 3 and Bendix CD V-750 Model 5. Bottom
row left to right: Jordan Electronics CD V-750 Model 5, Jordan Electronics
CD V-750 Model 5a, Industrial Electronic Hardware CD V-750 Model 5b, and
a FEMA issue S.E. INT'L Inc. CD V-750 Model 6. I have never seen any listing
of a CD V-750 Model 4.
This is a CD V-750 Model 5b dosimeter charger manufactured by Industrial
Electronic Hardware Corp. This unit is used, as seen in the picture at
the top of this page, to charge (zero) the dosimeters before use. The
dosimeter presses onto the charging contact on the upper left of the charger
and the hairline on the dosimeter's scale is zeroed by turning the large
knob on the upper right. The charging contact has a clear plastic bushing
that the contact passes through. There is a light bulb inside the charger
below the contact which comes on when the contact is pressed down and
allows the person charging the dosimeter to see the scale while charging.
You can see the markings showing which way to turn the knob, "up
scale" or "down scale". Some of these chargers can be tricky
to use and take quite a bit of practice to get a dosimeter zeroed on the
first try. These chargers use one D-cell battery for power. Click photo
to see larger.
V-750 Model 6
FEMA later released the CD V-750 Model 6, an electrostatic dosimeter charger
in the early 1990s. Instead of using batteries this charger generates
it's own charge to charge the dosimeters with a piezoelectric crystal.
The dosimeter is charged by working the large black lever until the hairline
moves down-scale past zero, then the hairline moves upscale slowly as
the black button, just above the lever, is depressed. The button is released
when the hairline reaches zero thus zeroing the dosimeter. The yellow
trigger-like lever latches the dosimeter in place in the charger. I find
it interesting that even though these were released by FEMA they still
have the Civil Defense logo prominently displayed on the label. This Model
6 charger is very easy to use.
Special Thanks to Mike for this CD V-750 Model 6!!
FEMA CPG 4-1 AC Dosimeter Charger Project
The FEMA CPG 4-1 Repair and Maintenance Manual For Radiological Instruments
Volume 6 Section 30 has instructions for building an AC powered dosimeter
charger. The CPG 4-1 states that this charger was to be built and used
by state maintenance and calibration shops. I thought it would be a cool
project to try to build but it proved a bit more of a pain than I thought
it would be. After it was all over and done with it was worth it though.
The aluminum box enclosure is still available from the original manufacturer
named in the parts list as is the power transformer but a new transformer
was too expensive so I watched eBay for a few months and finally found
a new one in the box for about $15. I was able to locate equivalent parts
from the information on the FEMA parts list. The one thing listed that
wasn't available was a modified charging contact. I robbed one out of
a non-working CD V-750 I had and modified it as best I could without seeing
the one that is listed on the parts list. I was pretty surprised when
the thing actually worked when it was finished! It charges dosimeters
easily and works pretty well overall. The box didn't come yellow, I painted
it. If you want to try to build the charger here is an Adobe Acrobat PDF
file of the instructions. CPG4-1ACCharger.pdf
400Kb file size.
FEMA CPG 3-1
FEMA CPG 4-1
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