AEROGRAPH3R'S MATE 3 & 2 



in LOW position. Clockwise rotation causes 

 needle of tramission meter and recorder pen 

 to move up- scale. 



RECORDER CONTROLS. — The following 

 controls are used in the operation of the recorder 

 section of the transmissometer. The recorder 

 switch is located in the rear of the indicator 

 unit and puts the recorder meter in movement 

 series with the transmission meter when in 

 the ON position. For the other controls see 

 figure 5-20. 



1. ZERO ADJUSTMENT LEVER. Adjusts 

 mechanical zero. Recorder pen moves in same 

 direction as lever. 



2. TRANSMISSION PEN. Draws inked line 

 on chart paper according to variable trans- 

 mission of airpath between projector and re- 

 ceiver. 



3. RANGE PEN. Records the position of 

 the range switch on the chart. 



4. CHART DRIVE CONTROL LEVER. Turns 

 chart drive clock mechanism on or off. To 

 start mechanism, move lever from Stop to 

 Start. If it does not start, repeat until it 

 starts. 



5. CHART DRIVE CHANGE GEARS. Deter- 

 mines the speed of the roll chart. Normal 

 chart speed is 3 inches per hour. 



Maintenance 



The maintenance which Aerographer's Mates 

 perform on the transmissometer set is of 

 a mechanical nature. The ship's or station's 

 electronics division performs the required 

 maintenance on the electronic components. 



PREVENTIVE MAINTENANCE. — To re- 

 move corrosion, use very fine sandpaper. Never 

 use emery cloth or steel wool within the 

 cabinets at any time, since the debris from 

 these materials are conductors and can cause 

 shorts between components. 



Keep both the interiors and exteriors of 

 the units clean. Use cheesecloth to clean the 

 cabinets and either cheesecloth or a camel's 

 hair brush to clean electrical components. 

 If necessary, except for electrical contacts, 

 moisten the cloth or brush with an approved 

 drycleaning solvent. After cleaning the parts 

 dry with a clean cloth. 



When cleaning the lenses, harsh or gritty 

 cleansers should be avoided. A soft, lint-free 

 cloth and clean water will usually be satis- 

 factory. When this is not sufficient, use a mild 

 cleanser meeting the Navy's standards. Do 

 not use cleansers which will leave an oily 

 residue on the glass. The cleaning process 

 should end with a dry, clean, film-free, deposit- 

 free, glass surface. 



LUBRICATION. — The indicator and re- 

 corder require semi-annual lubrication; the 

 projector, projector power supply, and receiver 

 require annual lubrication. Specific instructions 

 are contained in the technical manual for the 

 equipment. 



If the parts listed are gummy or excessively 

 dirty, clean with an approved drycleaning sol- 

 vent before oiling. 



CONVERTER-INDICATOR GROUP 

 OA-7900A/GMQ-10( ) 



Runway Visual Range (RVR) is a measure- 

 ment of the visibility along the runway through 

 the use of Converter-Indicator Group OA-7900 A/ 

 GMQ-10 in conjunction with the Transmisso- 

 meter AN/GMQ-10. RVV is an instrumentally 

 derived value that represents the horizontal 

 distance a pilot will see down the runway from 

 the approach end. Even though the equipment 

 is termed RVR converter, it is used to obtain 

 RVV and not RVR. 



Converter-Indicator Group OA-7900A/GMQ- 

 10 consists of Signal Data Converter CV- 

 3125/GMQ-10 and Digital Display Indicator 

 ID-1939/GMQ-10 as shown in figure 5-21. 



Theory of Operation 



As mentioned in the foregoing paragraph, 

 this equipment utilizes data from the Trans- 

 missometer AN/GMQ-10 for the computation 

 of Visibility (RVV). The transmissometer sup- 

 plies light transmittance signals in the form 

 of pulse rates. These pulse rates are transmitted 

 to the RVR converter where they are corre- 

 lated with the empirically obtained visibility 

 data encoded therein. The corresponding visi- 

 bility value is then displayed once every minute. 



The system Is designed to convert the 

 transmittance pulse rates to their corresponding 

 visibility values with a high degree of accuracy. 



98 



