changes allow the plotter scale to be changed at will 

 from 1" = 8000' to 1" - 4000' or 1" = 2000'. Special 

 gearing is available for 1" = 1000' . A solenoid pointer 

 marks the chart automatically. 



b. Hydrodist MRC/12 



(1) The MRC/12 is quite similar in function and operation to 

 its predecessor the MRC/2 and has additional digital read- 

 out and plotter equipment for automatic recording of 

 transit time . 



(2) Digital Display Unit type DDUl: the unit is self-contained 

 and provides a continuous integrated readout of the two 

 ranges as a digital display. It is intended for table-top 

 mounting and may be mounted remotely from the measur- 

 ing instruments . Each of the Fine A readings is con- 

 tinuously displayed on a dial that is scaled - 100. A 

 counter continuously integrates the A pattern rotations 

 and provides a direct readout of range. 



(a) Input: 1-kc amplitude modulated sine waves 



(b) Power: 1 amp at 24/27 v dc . 



(3) Recorder: the unit is two -channel thermal writing with 

 a polarized event marker indicating ambiguous phase 

 difference readings . The recorder pen moves from the 

 bottom to the top of the chart as, for example, the A 

 range changes from 0-50 meters. It moves from top 

 to bottom as the range increases from 50- 100 meters. 

 An identical trace would be produced from top to bottom 

 as the range decreased from 50-0 meters, thus produc- 

 ing an ambiguous reading. 



(4) Ambiguity is resolved by direction of the relay-operated 

 event marker. Thus, the direction of the ambiguity pen 

 deflection, in combination with the reading trace, deter- 

 mines whether the range is increasing or decreasing. 



154 



anbitr ZD.Hittlf.ilnr. 



