1、SAE AIR*LOO 69 8357340 0003Li73 9 I AEROSPACE I N FO RM AT1 O N SPACE REP 0 KT Society TWO PENNSYLVANIA of Automotive PLAZA, NEW Engineers, YORK. N Y Inc. 10001 AIR 1090 Issued 10-1-69 Revised -.- IGNITION EXCITER OUTPUT VOLTAGE PULSE MEASUREMENT USING A PRESSURIZED BALL GAP : - c. PURPOSE The purpo
2、se of this report is to provide reference information for equipment and procedure to be used in measurement of high tension ignition exciter output voltage pulses using a pressurized ball gap. SCOPE This report includes a procedure for typical pulse voltage measurement using the pressurized ball gap
3、, calibration procedure, and a description of the pressurized ball gap. _- 1. INTRODUCTION 1.1 1.2 1.3 1.4 1.5 The high tension capacitor discharge ignition system produces an initial ionizing voltage of a magni tude as large as necessary (within design limits) to ionize the gap of the high tension
4、igniter. The rise time of the ionizing pulse (zero to peak voltage) approximates one microsecond in most high tension ignition systems. The magnitude of the ionizing pulse is determined by the high tension ig- niter demand under the conditions of pressure, temperature, and atmosphere within which it
5、 is re- quired to ionize. Determination of the output pulse magnitude is important since sufficient voltage must be supplied from the exciter to ionize the spark igniter. It also may be desirable to determine the maximum output voltage pulse magnitude so that leads and terminations are not damaged s
6、hould the spark ig- niter be quenched. These requirements to determine minimum and maximum output pulse voltage amplitude of high ter sion exciters require measurement equipment that is responsive to the output pulse rise time and magnitude and is reasonably repeatable. Since inspection test criteri
7、a usually establish go-no go levels, the pressurized ball gap lends itsel to this type of requirement. Specific determination of output voltage pulse magnitude may also be made. The pressurized ball gap described herein is adequately sensitive, consistent and stable to produce the desired results. c
8、uracy and subsequent use such as: It minimizes the shortcomings which have existed in the past that affect ac- a. b. c. Oxidation of electrodes d. Poor ionization characteristics e. Poor resolution and readability f. Method of calibration Effects of barometric pressure and relative humidity Stray ca
9、pacity effects caused by nearby grounds Copyright 1969 by Society of Automotive Engineers, inc. - Printed in U.S.A. - SAE AIR*KLOSO 69 W 8357340 0003474 O W 2. 3. 3.1 3.2 -2 - SPECIFICATIONS FOR PRESSURIZED BALL GAP The general specifications for the pressurized ball gap described by this report are
10、 as follows: Range: 5 to 30 KV Peak Voltage Risetime: Designed to measure pulses with zero to peak voltage rise times of 800 nanoseconds to 50 microseconds Accuracy: Operating Pressure: Pressurizing Gas: Dry Nitrogen Construction: Weight: 50 lb Internal Capacitance: 25 pf Fig. 1 shows the pressurize
11、d ball gap described. PROCEDURE FOR TYPICAL PULSE VOLTAGE MEASUREMENT USING PRESSURIZED BALL GAP - -t 1% of full scale from ref. std. 800 torr (mm Hg) Sealed system with controlled purge rate Test Method Configuration a. Fig. 2 shows an exciter unit with associated ball gap used for pulse voltage me
12、asurement. b. Fig. 3 is a block diagram showing the equipment arrangement used in the measurement. Detailed Procedure for &-No Go Requirement a. Connect a dry nitrogen tank to ball gap and adjust pancake regulator at top of ball gap to produce 800 torr absolute pressure on indicator. A size 1A gas b
13、ottle is recommended and will furnish approxi- mately 48 hr of gas supply. b. If ball gap has not been in continuous use, allow to purge one-half hour minimum to guarantee a homo- geneous gas flow. c. Insure that proper capacitance loading applicable to test piece is applied across exciter output. T
14、he total load must include the internal capacitance of the ball gap. d. Connect exciter output to appropriate “HV“ and “GND“ terminals of the ball gap. e. Obtain desired specification lower voltage limit and convert to dial divisions on the ball gap turn count- ing dial through use of calibration cu
15、rve of ball gap. See Fig. 4 for a typical curve. f. Energize unit. Ball gap should fire consistently for prescribed period of time dictated on specification for exciter unit. g. Obtain desired specification upper voltage limit and convert to dial divisions on the ball gap turn counting dial through
16、use of the calibration curve. Energize unit. Ball gap should not fire for the prescribed period of time dictated on the specification for the exciter unit. h. SAE AIR*LOSO 69 m 8357340 0003475 2 m -3- 3.3 Specific Determination of Maximum Output Voltage Pulse a. To obtain a specific coming-in or fir
17、ing point, proceed as above except initially adjust ball gap turn, counting dial to insure non-firing by adjustment to a voltage level much higher than expected. b. Energize unit and, if firing does not occur, decrease ball gap spacing at about five division incremen._ until consistent firing occurs
18、. c. Convert ball gap turn counting dial divisions to output KV via calibration curve of gap. Initial gap setting must be to the non-firing side to eliminate the “drawing-out“ effect when approaching from the opposite direction. 4. CALIBRATION OF THE PRESSURIZED BALL GAP 4.1 Calibration Method Confi
19、guration Calibration of the subject ball gap can be done with a certified one-half percent of full scale electrostatic voltmeter in conjunction with a high voltage pulse calibrator (Ref. ALR 1091). equipment and connections required for calibration. Fig. 5 shows the associated 4.2 Detailed Calibrati
20、on Procedure a. b. C. d. e. f. g. h. i. j. Connect a dry nitrogen tank to the ball gap and adjust the pancake regulator to indicate 800 torr ab- solute pressure on the gauge. Allow ball gap to purge a minimum of one-half hour to guarantee a homogeneous gas flow. Adjust turn counting dial at front of
21、 HV pulse calibrator at a point sufficient to guarantee non-firing of the internal switch. Using the “HV Coarse“ and “HV Fine“ control knobs on the front panel of the HV pulse calibrator, set desired test voltage on the electrostatic voltmeter. Set turn counting dial on ball gap to the non-firing si
22、de of the test point (usually test point plus 10 dial divisions). Refer to typical ball gap curve, Fig. 4. Decrease the internal switch spacing in the HV pulse calibrator with turn counting dial on front panel to initiate ball gap firing. If ball gap does not fire, repeat steps c and d with test bal
23、l gap vernier set one division lower each time until firing occurs. Repeat procedure at this setting as often as is felt necessary to guarantee that a consistent firing point has been established. Record this dial setting. Proceed to check ball gap over the range of 5 to 30 KV at one KV increments.
24、Following initial calibration or after any remedial action has been taken, a curve of dial divisions vs kilovolts should be plotted and attached to ball gap. Subsequent calibrations of the ball gap must maintain 2 9 dial divisions of the attached curve to be a valid calibration. 5. DESCRIPTION OF TH
25、E PRESSURIZED BALL GAP 5.1 The ball gap assembly is essentially a sealed system employing a controlled purge rate of dry nitrogen ga Purging is performed to eliminate oxide formation on the interior of the gap and is accomplished with a pipe plug exhaust vent placed in the side of the exterior Bolta
26、ron case. Lost gas is replaced utilizing a pancake regulator so that internal gas pressure remains at 800 torr. Internal pressure is monitored with an absolute-pressure indicator spanning 400 to 800 torr. SAE AIR*LOO 69 M i3357340 O003476 4 M - _ 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 -4- An absolute press
27、ure of 800 torr was selected because it is higher than ambient environmental pressure ir areas where the gap is to be used. It is imperative that the working pressure be higher than ambient, since breathing will result if opposite is true and this would result in oxygen, water vapor, and other con-
28、taminants being forced into the gap. This pressure also affords easy control, measurement, and envelop( fabrication. Dry nitrogen gas was selected as a pressurizing medium because it is non-oxidizing under the conditions of use, it ionizes easily, is relatively inexpensive, and is available in pure
29、form with controlled moisture content. Most important, however, is that it yields full travel of the balls over the desired voltage range with good resolution. Nitrogen entering the ball gap cavity is directed by means of a nylon tube under the teaser. This reduces inconsistencies due to varying gas
30、 conditions in the area of the ionization teaser after firing. Resolution and readability of the instrument is accomplished with a gear mechanism driven by a turn counting dial. (Ref. Fig. 6 and 7.) The dial covers 10.turns with calibration allowing readings to the nearest O. O1 turn. The complete r
31、ange of the turn counting dial, with gearing used, covers approximately O. 4 in. of ball separation or 400 micro. inches per dial division (about 30 volts). The actual gap employs chrome steel balls 1.5 in. in diameter with tungsten inserts at all points where wear from sparking is likely to occur.
32、This includes the main spark discharge area and the section of the ball which is directly under the ionization teaser. These inserts are silver brazed into the ball and then the bail is reground to its original spherical shape before installation in the gap mechanism. Ionization of the ball gap is a
33、ccomplished with a tungsten teaser. Also, attached to the teaser is a brass disc which produces better capacitance coupling between the teaser and the high voltage ball (see Fig. 6). The tangential spacing between the teaser tip and high voltage ball is fixed at O. O02 in. The vertical dis- tance be
34、tween the top of the ball and teaser tip is controlled to O. 05D where D is the ball diameter (see Fig. 8). The external Boltaron housing is lined in the gap compartment with a thin brass sheet to fix a ground plane reference for the purpose of defining stray capacitance effects. 6. REFERENCES “Deve
35、lopment of a Device for Measuring Pulse Voltages“ by D. Michel, Electrical Components Division, The Bendix Corporation. AIR 1091, “High Voltage Pulse Generator“ AIR 1092, “High Tension Exciter Output Voltage Measurement Using The Cathode -Ray Oscilloscope“ (Alternate Measurement Method) PREPARED BY
36、SUBCOMMITTEE E-30A AIRCRAFT GAS TURBINE AND RAM-JET ENGINE IGNITION, OF COMMITTEE E-30, IGNITION RESEARCH . -5- FIGURE 1 - PRE8SURIZED BALL GAP t -6- - 7- VARIABLE LOAD PRESSURIZED BALL GAP FIGURE 3 - BLOCK DIAGRAM OF EQUIPMENT SET-UP 800 600 490 209 14 18 22 26 30 BREAKDOWK KILOVOLTS PEAK FIGURE 4
37、- TYPICAL CALIBRATION CURVE FOR PRE88URaZED BALL, GAP P . -1 -u y FIGURE 6 - CAUB%llhT%ON SET-UP OF PRESSURIZED BALL GAP -9- FIGURE 6 - BALL GAP DRIVE - . -.* 8357340 00Q3bi82 T - 10- FIGURE 7 - TURN COUNTING DIAL ON BALL GAP l i SAE AIR*1070 69 8357390 0003983 1 - 11- TEASER, Tungstei 1/8 dia. X 1 in. f. 002 . o75 BALL, Steel, 1 1/2 in. dia FIGURE 8 - BALL GAP ASSEMBLY DIMENSIONS i,
