CD V-750
And Dosimeters

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CD V-750 Dosimeter Charger and Dosimeters

Charger with Dosimeter on contact 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 The CD V-730s and CD V-740s were early dosimeters that were superseded by the CD V-742.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 these produced.
CDV 138 Scale View

CD V-138 Dosimeter

Range 0-200 Milliroentgens
Reads Gamma Radiation
Low range dosimeter used for training.
221,866 produced.
CDV 730 Scale View

CD V-730 Dosimeter

Range 0-20 Roentgens
Reads Gamma Radiation
Superseded by CD V-742.
168,500 produced.

CDV 740 Scale View


CD V-740 Dosimeter

Range 0-100 Roentgens
Reads Gamma Radiation

Superseded by CD V-742.
162,950 produced.



CD V-742 Dosimeter

Range 0-200 Roentgens
Reads Gamma Radiation

3,117,201 produced.

New Version CD V-138 And CD V-730 Dosimeters By Arrowtech Inc.

New CDV 138 Scale View

New CD V-138 Dosimeter

Range 0-200 Milliroentgens
Reads Gamma Radiation
Low range dosimeter.
New CDV 730 Scale View

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.


CDV 750 Charger Picture 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.



CD 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.


References

FEMA CPG 3-1
FEMA CPG 4-1 Civil Defense Training Filmstrip Frames Click to see larger

CD Training Filmstrip Frame
CD Training Filmstrip Frame
CD Training Filmstrip Frame
CD Training Filmstrip Frame