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CD V-781 Aerial Monitoring Set
The CD V-781 Aerial Monitoring set was intended for use in aircraft for
monitoring by air. This set consists of a tape recorder, for recording readings
by voice while flying, detector unit (yellow box), mounting brackets, meter
unit (black box with meters) and a simulator unit (green box with meters)
for verifying operation of metering unit.
Individual Components of the CD V-781
All description text is from the CD V-781 instruction manual.
CD V-781 Metering Unit
The metering unit includes three indicating meters with associated indicator lamps, an audio tone generating circuit, a low-voltage regulating circuit, and provision for interconnection of the unit with the aircraft electrical and radio systems as well as the detector unit. It functions as the read-out portion of the instrument system, giving both audio and visual indications of prevailing radiation levels. As in the detector unit , all circuits are transistorized and circuit boards are removable without disconnection to facilitate maintenance or repair. Click photo to see larger.
CD V-781 Detector Unit
The detector unit includes three Geiger-Mueller (G-M) tubes, each responding to a decade portion of the total 0-10 R/hr radiation level range of the instrument, associated count-rate circuitry, a regulated high-voltage power supply circuit, and auxiliary batteries. These batteries (NEDA No. 13) are capable of operating the system for appoximately 40 hours. Standard D-cells other than NEDA No. 13 can be used to operate the system for appoximately 25-30 hours.
The unit functions to measure diffused gamma radiation in the 70kev to 1.2Mev spectrum, and to convert the measured intensity level to a corresponding current to drive the metering unit. All circuits are transistorized and circuit boards are removable without disconnection of the circuits to facilitate maintenance. Sensitivity adjustments are provided in the count rate circuits for calibration.
Click photos to see larger.
CD V-781 Simulator Unit
The simulator unit is a training device intended to substitute for the detector unit on training missions. It includes an auxiliary battery power supply, and provides for interconnection with the metering unit in the same manner and the detector unit. Instead of the G-M tubes and count-rate and high-voltage circuitry however, in contains a simple externally controlled circuit enabling an instructor to insert predetermined readings into the metering unit. A set of three meters, identical to those in the metering unit, indicate what readings are being generated, and the metering unit responds to the same radiation level (reading) established in the simulator unit. The meter driving circuit is transistorized and circuit boards are removable without disconnection. Adjustments are provided to make the simulator unit meter readings track properly. Click photo to see larger.
CD V-781 Tape Recorder
The tape recorder unit provides oral recording of radiation level date observed in the course of a mission, together with correlated position fixes and altimeter readings. After completion of the aerial survey mission, the data is evaluated and used to plot corresponding ground level dose values for he area covered by the mission. A remote switch is provided to control the tape drive. The throat microphone can be worn by the pilot without interfering with normal radio communications. Click photo to see larger.
Here are a couple of photos of a CD V-781 operating with the simulator unit. This CD V-781 unit was found in storage and was originally in service with a Civil Air Patrol member. Notice how the meters on the simulator unit (green unit on bottom) correspond with the meters on the metering unit (black unit on top) in each photo. The CD V-781 has two indicator lights above 2 of the indicating meters. There is an amber light above the center meter and a red light above the right meter. As the reading progresses above the range of the left (lowest range) meter the center meter begins indicating and the amber light activates as seen in the left photo. As the reading increases above the range of the center meter the reading is indicated on the right hand (higher range) meter. The red light above that meter then comes on and the amber light goes out.
CDV-799 Aerial Survey Meter Electronic Calibrator
The CDV-799 was issued in 1980 by FEMA. This unit was to be used only on retrofitted CD V-781s. The CDV-799 uses electronic pulses to allow calibration of the Aerial Meter without a radioactive source. I don't know what the retrofit of the CD V-781 involved but the CD V-781 pictured above does have the "R" for retrofit on the Metering Unit and the Detector Unit. I haven't tried to hook it up to the CD V-781 to see if it works yet. I do have the instruction manual for the CDV-799 in pdf format. CDV-799 manual. You will need Adobe Acrobat to read the manual file.
A very special Thanks to Rob Stone of Portsmouth, Ohio for this unit and the scan of the manual!