RECORDING TRANSMISSION MEASURING SYSTEM 



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recording meters used in the standard volume indicators. Records of 

 telephone circuit noise, which sometimes fluctuates in magnitude, can 

 also be recorded. This high recording speed is made possible by mak- 

 ing use of the fact that a record can be made on heat-sensitive paper 

 without actual contact between the heat source and the paper and, 

 therefore, without friction between the paper and the moving system 

 which carries the heat source. Of particular importance is the fact 

 that there is no static friction between these parts so that the power 

 required to turn the moving system is only that necessary to overcome 

 inertia, restoring spring force, damping and pivot friction, as is the 

 case with an ordinary indicating meter. 



Figure 3 illustrates the general principles of this recorder. Heat- 

 sensitive paper is drawn over a straight bar which is at right angles to 



Fig. 3 — Diagram illustrating recording principle. 



the direction of paper movement, the bar being shaped so that only a 

 line of paper is directly below the pointer of the moving system. A fine 

 straight electrically heated wire is placed on the end of the pointer so 

 that as the current through the moving system is varied the hot wire 

 travels at approximately right angles to the line of the exposed paper 

 and only a small spot of the paper is affected by the heat at any instant. 

 With this arrangement the plot obtained has rectangular coordinates, 

 which is a very desirable feature. 



The heat-sensitive paper is a colored paper coated with white wax 

 and before exposure is nearly pure white. The application of heat 

 causes the wax to melt and be absorbed by the paper, making a distinct 

 colored trace. The rapidity of action is dependent upon the amount 

 of heat and the rate of movement of the heated wire with respect to 



