ELECTROFORMED CONDUCTOR FOR TELEPHONE DROP WIRE 1129 



temperature is recorded by an instrument attached to the outer trough 

 of each process on the mezzanine floor. In addition to recording tempera- 

 tures, the instrument also operates a spring loaded valve, by air pressure, 

 in the heat exchanger piping. The correct operating temperature can be 

 chosen by setting the manually operated pointer on the recording chart. 

 Automatic, electrically operated, liquid level control devices have been 

 provided for each solution. These controls are provided for the following 

 reasons : 



1 . The evaporation of water from the solutions used in the process is 

 of such magnitude that some means of maintaining solutions within 

 their proper concentration range is necessary. 



2. The solution level in the storage tank must not reach a specified 

 lower limit, or the circulating pump suction head will fall below the mini- 

 mum operating value. 



3. When the electroforming machine is in operation, the total solu- 

 tion volume in any unit process is composed of the portion in storage 

 and the portion in circulation. If the portion of solution in the storage 

 tank exceeds a known value, the remaining volume of storage space will 

 be insufficient to accommodate the circulating portion of solution which 

 returns to storage when the machine is shut down. 



The liquid level control device consists of four electrodes which dip 

 into the contained solution. The four electrodes are arranged so that as 

 the level varies, the solution closes different electric circuits. During nor- 

 mal operation at proper level, the electrical connection between the low 

 electrode and a common electrode holds the solenoid operated water 

 valve closed. When the level falls about J^" below the prescribed level, 

 the circuit opens and releases the solenoid water valve to the dragout 

 recovery cell or the valve in the water line leading to the filling nozzle 

 in the storage tank. When solution again rises to the prescribed operating 

 level, another tripping circuit is activated which causes the water valves 

 to close. 



In order to show whether or not the level controls are operating satis- 

 factorily, a red and a green light are mounted above and in line with 

 each storage tank. When the green light is on, the levels are proper. The 

 red light is a signal that the level is increasing beyond the point at which 

 the tripping circuit should have been activated. In this case, the water 

 valve is immediately turned off. When both lights are on, the solution 

 level in the reservoir is low and make-up water is added automatically. 



Due to the chemical action of fluoboric acid on the copper anode ma- 

 terial in the acid copper plating bath, the copper concentration of the 

 solution rises during operation of the electroforming machine. In order 



