1、b SAE AIR*wLOSL 69 357340 0003Yli 3 - I hence, it is traceable to known accuracy. The pulse generator has been designed primarily for the purpose of calibrating a pressured ball gap measurement instrument. However, it may be similarly used to calibrate specific points of a volt- age divider probe. T
2、he pulse generator design to be described provides the following: a. Accurate output voltage. b. Zero to peak voltage time to be less than one microsecond with no overshoot. c. One pulsed output. d. Infinitely variable from five to thirty thousand volts. e. Constant waveform. f. Capability of being
3、reproduced. Fig. 1 shows a photo of the pulse calibrator described connected to a pressurized ball gap. shows a typical output waveform from the pulse calibrator. Fig. 2 Copyright 1969 by Society of Automotive Engineers, Inc. Printed in U.S.A. SAE AIR*KLOSL 69 8357390 0003985 5 -2 - 2. PROCEDURE FOR
4、 USE OF PULSE GENERATOR TO CALIBRATE PRESSURIZED BALL GAP (REF. AIR 1 o9 O) a. Connect a dry nitrogen tank to the gap and adjust the pancake regulator on the ball gap to indicate 800 torr absolute pressure on the gauge. b. c. Allow gap to purge a minimum of one-half hour to guarantee a homogeneous g
5、as flow. Adjust turn counting dial at front of HV pulse generator at a point sufficient to guarantee non-firing of internal switch. Using the IIHV COARSE“ and “HV FINE“ control knobs on the front panel of the HV pulse generator, set desired test voltage on electrostatic voltmeter. d. e. Set turn cou
6、nting dial on ball gap to the non-firing side of the test point (usually test point plus ten dial divisions). f. Decrease the internal switch spacing in the HV pulse generator with turn counting dial on front panel to initiate ball gap firing. g. If ball gap does not dire, repeat steps c, d, and f w
7、ith test ball gap vernier set one division lower each time until ball gap fires. Repeat procedure at this setting as often as is felt necessary to guarantee that a consistent firing point has been obtained. Record this dial setting. h. Proceed to check ball gap over range of 5 to 30 KV at one KV inc
8、rements. i. Following initial calibration or after any remedial action has been taken, a curve of kilovolts versus dial setting should be plotted and attached to ball gap. Subsequent calibrations of the gap must maintain 2 9 dial divisions of initial data to be a valid calibra- tion. j. 3. DESCRIPTI
9、ON OF PULSE GENERATOR The pulse generator is actually constructed in three portions. These are power supply and primary con- trols, leads and grounds, and high voltage components. 3.1 Power Supply and Primary Controls 3.1.1 The power supply used in the pulse generator is a commercial grade 40 KV pow
10、er pack in a shielded case. Most present day commercial power supplies would probably work if, in their fabrication, good high voltage practices of connections, grounds, and internal shielding, among others were utilized by the manufacturer. 3.1.2 To regulate and control the output voltage of the po
11、wer supply, autotransformers were used. One was a constant voltage transformer for line regulation, the others were variable autotransformers providing coarse control over the full voltage range and fine control of only several hundred volts at any setting of the coarse control. 3.1.3 Some means was
12、 necessary to signal the operator that the pulses were generated since the output was inaudible. A commercial audio amplifier and speaker system was installed, and an inductive pickup coil was placed in close proximity to one of the wires carrying the pulse. Thus when the generator fired, an audible
13、 click could be heard in the speaker, freeing the operators vision for observation of the ball gap in calibration. SAE AIR*LOSL 63 9 8357340 0003486 7 -3- 3.2 Lead and Grounds: The calibrator was constructed with a one point ground made of a solid copper block into which all grounded components and
14、leads were individually connected. Pure copper tube 1/2 in. diameter with 1/16 in. wall was used for general connections and ground wire. 3.3 High Voltage Components These are resistors, capacitors, and the trigger switch (Reference S-1 of Fig. 3 and 4). 3.3.1 The capacitors used in the generator we
15、re extended planar foil capacitors. Standard Bendix capacitors were beefed up to withstand 50,000 volts DC or used as is depending upon the application. The capacitors were encased in an oil bath to insulate them from nearby metal structures and keep them thermally con- stant during use. 3.3.2 The r
16、esistors were standard, high voltage, non-inductive carbon film resistors commercially available. 3.3.3 The trigger switch is a three electrode controlled gap as shown in Fig. 5. The third electrode, the teaser, is a needle pointed rod of tungsten perpendicular to the axial line of the major electro
17、des and is insulated from them and ground. 3.3.3.1 The low electrode is installed on a threaded shaft and mechanically geared to a ten turn dial indicator. All gears and shafts were spring loaded to insure repeatable gap distance for any given dial indication. One dial division moves the low electro
18、de 416.6 microinches. approximately .375 inches. At 900 dial divisions, gap spacing is 3.3. 3.2 The electrodes are 1 in. chrome steel balls. The area of the balls where firing occurs and the area around the teaser were milled out and plugs of pure tungsten were inserted, brazed, and ground down to f
19、ollow the contour of the ball. 4. PULSE GENERATOR ACCURACY The accuracy of the pulse generator is presented in Table 1. of the electrostatic voltmeter which is O. 5% of full scale value. Not included in the tabulation is the accuracy Table 1 Pulse Generator Accuracy Standard Voltage 2,500 5,000 10,0
20、00 15,000 20,000 25,000 30,000 Losses 107.7 115.3 130.7 146. O 161.4 176.7 192.1 % Error 4.28 2.31 1.31 o. 97 O. 81 O. 71 O. 64 - SAE AIR*LOL b 8357390 0003487 7 = - 4- 5. REFERENCES “Development of a High Voltage Pulse Generator“ by J. P. Dombrowski, Electrical Components Division, The Bendix Corpo
21、ration. AIR 1090, “Ignition Exciter Output Voltage Pulse Measurement Using a Pressurized Ball Gap“. AIR 1092, “High Tension Exciter Output Voltage Measurement Using the Cathode-Ray Oscilloscope“ (Alternate Measurement Method) SUBCOMMITTEE E-30A PREPARED BY AIRCRAFT GAS TURBINE AND RAM-JET IGNITION,
22、OF COivMITTEE E-30, IGNITION RESEARCH B D D -5- T7 d FIGURE 1 - PUME CALIBRATOR CONNECTED TO PRESSURIZED BALL GAP = 30KV El Horizontal = , 2 ps/division Ver tical = 5KVfdivision FIGURE 2 - OSCILLOGRAM OF OUTPUT OF GENEFUTOR USING TEI(TPRON%X 535 SCOPE WITHTYPE CAPLUGINABENIDIXHIGHVOLTAGE PROBE Suppl
23、y R2 - 100 M M - Electrostatic Voltmeter ci - -042 MFD 50KV CZ - 100pf 30KV R1 - 1000 Ohms 15KV S-1 - Ball Gap - Special FIGURE 3 - CHARGE TRANSFER GENERATOR (SIMPLIFIED DIAGPtBM) SAE AIR*LOSL 67 83573LiO 0003LiO 9 -7- -I /J / . / w c z / ;y- /- -=-: Voltage Input Teaser J FIGURE 5 - TEASER TYPE BAL
24、L GAP - SAE AIR*LOSL 69 83573LiO 0003492 2 -9- Appendix I Theoretical Description of Charge Transfer The charge transfer generator is based on the premise that if a capacitor with no charge is connected across a capacitor with an initial charge, there will be no charge loss even though there will be
25、 voltage drops and energy losses. If in Fig. 3 at t = O: E, is the voltage across capacitor C1; E, is the voltage across S1; and E2 is the voItage across capacitor c2, then: Q C1 Q C1 E1 = ; Es = -Ei; E2 = O and at t =. O: Ei = 2 ; Es = -(Ei - Eg where, Qt= QI + Q2 and Qt, Cl, Cg, El, Es, E, and Es
26、are known values. After operation of S1, equilibrium conditions exist and: From the above it can be shown that: GC1 c1+c2 cl+% EC Eq= 1 1 - (3) E2 = .99693 (El - G) (4) The switch in the transfer generator is actually an adjustable ball gap and never mechanically closes. There- fore, it has an extin
27、guishing voltage Es1 at which the arc cannot be mainaned. The value of this voltage is treated as an empirical value since it is dependent upon many factors not considered in this analysis. 163230 probes and a Tektronix type 535 oscilloscope using a type CA plug in unit as a differential amplifier. Measured values ranged from 25 to 100 volts. If a value of about 100 volts is assigned as the extinguishing volt- age, expression (4) above simplifies to: A measurement of the extinguishing voltage was made at 3000 volts using two Bendix 10- E = .99693 E - 100 (5 ) 2 1 o
