From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The function, efficiency, and life of Erie Suppressors for eliminating ignition interference in automobiles.
| Identifier | ExFiles\Box 168b\1\ img143 | |
| Date | 30th December 1938 guessed | |
| ERIE SUPPRESSORS ERIE RESISTOR LIMITED manufactures a complete line of suppressors for use in eliminating high tension interference caused by ignition on radio equipped autos. When radios were first developed for automobiles, this interference—commonly referred to as "motor noise"—proved to be one of the major obstacles in the way of efficient reception. After trying several different methods it was found that the best means of removing this interference was to place a resistance unit in series with each high tension cable at the spark plugs and distributor, and to use by-pass condensers on the generator at the source from which the power for the radio is taken. Though the general construction of suppressors has remained essentially the same as it was years ago—a moulded carbon resistance unit enclosed in an insulating case—the Erie Suppressors on the market to-day are a vast improvement, both in mechanical design and electrical efficiency, over the early ones. VOLTAGE COEFFICIENT Figure 1 Research work by the Erie engineering department points to the fact that "motor noise" is not caused by the low-frequency spark discharge itself, but rather by accompanying radio frequency impulses set up in connection with the discharge, and of a frequency determined by the distributed constants of the circuit. In effect, each spark plug acts as a small but troublesome radio transmitter. The function of the suppressor is to dampen or cut down the amplitude of this high-frequency discharge without seriously reducing the energy in the low-frequency discharge, which is necessary for proper ignition. To do this the suppressor must maintain substantially constant resistance during the entire period of each discharge. This is not possible unless the unit has a low voltage coefficient. Voltage coefficient is determined by the change in resistance when measured first at a low voltage and then at a higher voltage. If the resistance remains practically unchanged at the peak voltage of the discharge, the suppression is accomplished with greater efficiency. The low resistance drop of Erie Suppressors in comparison with "X" suppressors, having high voltage drop, is shown in Figure 1. Figure 1 Data: Y-Axis: Resistance Change - % X-Axis: Resistance - Ohms Chart Legend: Average Voltage Coefficient ½ watt suppressors measured at twice and ½ load. Curves: ERIE SUPPRESSORS, "X" SUPPRESSORS SUPPRESSION EFFICIENCY Figure 2 An efficient suppressor must not only eliminate "motor noise," but must do it without adversely affecting the operation of the automobile motor. The combination of raw materials that make up the resistance unit in Erie Suppressors accomplishes both of these functions. Dynamometer tests run in the laboratories of several leading automobile manufacturers under the supervision of their engineers, definitely prove the absence of any increase in gasoline consumption or loss of power when Erie Suppressors are used. Laboratory measurements run under conditions more severe than in actual use show that with Erie Suppressors it is not necessary to use excessively high resistance values to obtain adequate suppression. Maximum efficiency is reached at approximately 20,000 ohms, although there is not much gain above 15,000 ohms, as shown in Figure 2. The dotted curve represents the results obtained with "X" suppressors which, as shown in Figure 1, have poor voltage coefficient. With this type it would be necessary to use a 50,000 ohm value to obtain reduction of "motor noise" equal to that of a 10,000 ohm Erie Suppressor. When specifying resistance values of suppressors, remember that there is a definite relationship between suppression efficiency and voltage coefficient; and that different makes of suppressors of the same resistance value are not necessarily equally efficient in reducing "motor noise." Figure 2 Data: Y-Axis: Suppression Efficiency - % X-Axis: Resistance - Ohms Chart Legend: Average Suppression Efficiency, Air gap .200", Primary voltage 6.0 Curves: ERIE SUPPRESSORS, "X" SUPPRESSORS LIFE Many suppressors will drop considerably in resistance value after a few thousand miles of use, thus decreasing their suppression value. The drop in Erie Suppressors is very low—at room temperature, as shown in Figure 3, the maximum drop occurs after approximately 6,000 miles of use, where the change is—.75 per cent. After 35,000 miles maximum positive change of .55 per cent. occurs. From this point on the change is negligible. Figure 3 Figure 3 Data: Y-Axis: % Change-Resistance X-Axis: Distance - Miles Chart Legend: Average Room Temperature Load Change, Ambient temperature atmospheric, Load ½ air gap, Primary voltage 6.4 volts, Speed 40 M.P.H. 3 | ||