1、 FORD LABORATORY TEST METHOD BV 003-04 Date Action Revisions 2000 12 01 Revised Editorial no technical change A. Cockman 1992 08 11 Printed copies are uncontrolled Page 1 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST Application The Vibration Dampening Test rates the
2、dampening efficiency of various types of floor pan mastics, spray-on sound deadeners, combination materials used as instrument panel insulators and carpeting. Apparatus Required Audio Oscillator and Amplifier (Exciter Unit) Drawing ZX-824-9 or equivalent An R.C. type audio oscillator utilizing a 6SJ
3、7 and a 6F6 type tube is the oscillator circuit. One section of a dual triode tube, 6SN7GT, is used as a driver for two 6L6 tubes connected in parallel and the other section of the 6SN7GT is used as a cathode follower (a source of low impedance output which can be used in calibrating the timing desc
4、ribed later). The oscillator has a frequency range of 2 to 20,000 c.p.s. The plate load for the 6L6 tubes is the magnetic driver unit. It consists of a Thordarson type T-13C30 choke which has been modified by rotating the laminations so the core is open. When the unit is mounted close to the steel p
5、late, the steel plate completes the magnetic circuit and when energy is applied to the driver from the exciter unit, the plate will vibrate. Sound Decay Timer - Drawing ZX-879-2 or equivalent The sound decay unit consists of two amplifiers on a common chassis. One amplifier is the start amplifier an
6、d the second is the stop amplifier. The start amplifier utilizes two 6SJ7 tubes, both connected as triodes, one 6H6 dual diode as a full wave signal rectifier and a Type 2050 Thyratron which acts as an electronic switch for the clock. The signal is amplified by the two 6SJ7 tubes and then rectified
7、by the 6H6 and the rectified negative bias is applied to the grid of the 2050 tube. When the input signal decreases to a point where the negative bias on the 2050 tube falls to the “firing“ point, the tube will ignite and the clock will start. The input signal level at which the “firing“ occurs depe
8、nds upon the settings of the start attenuators. The START amplifier will “kick in“ at approximately 2 volts, as indicated by the meter. In order that a correct timing is obtained, it is necessary that the meter reads more than 2 volts before timing is started. A toggle switch located in the rear of
9、the Sound Decay Timer will connect the voltmeter in the STOP thyratron circuit, thereby measuring the negative bias on the tube. The STOP thyratron will “fire“ at about 2 volts also. Magnetic Driver The driver mounted under the center of a test panel excites the steel plate by a varying magnetic fie
10、ld. FORD LABORATORY TEST METHOD BV 003-04 Page 2 of 11 Copyright 2000, Ford Global Technologies, Inc. Permanent Magnet Loudspeaker This is used as a microphone. High Speed Clock Standard Electric Time Co. Type S-1 or equivalent. Regulated Power Supply To be used with clock as required. Vacuum Tube V
11、oltmeter Ballantine Model 300 or equivalent. Steel Panels 20 x 20 x 1/4 inch steel. Panels cut, not sheared, from the center of large sheets of cold rolled low carbon steel. Uniform thickness of the steel panel is required. Center cuts of sheet required to minimize the internal stresses found in out
12、er edges. The edges of the panel must be carefully ground to obtain the desired resonant frequency. Stop Amplifier The second amplifier is the stop amplifier. It consists of a 6SJ7 (triode connected as the input tube), a 6SJ7 (pentode connected) and a 6SN7GT, dual triode (connected as a two-stage am
13、plifier). The remainder is assembled the same as the start amplifier with the exception of the relay coil in the 2050 plate circuit. When this tube “fires“, the circuit is broken to the clock motor and the clock stops. One peculiarity should be noted in the circuitry of the stop amplifier circuit; t
14、hat is, the triode connected 6SJ7 followed by a 6SJ7 connected as a pentode. If the first 6SJ7 were connected as a pentode, the input circuit would be overloaded with a high starting signal and would be in error in timing. With the modified wiring, the maximum starting voltage at the input grid is a
15、bout 6 volts whereas first pentode connected 6SJ7 would initiate a maximum voltage of about 1.5 volts. Sound Decay Timer Notes After an initial warm-up period of about 30 minutes, an input signal is applied to the timer. This can be done either by exciting a steel plate or by coupling the input of t
16、he sound decay timer to the cathode follower output of the Exciter Unit. To facilitate the calibration procedure, it is necessary to disconnect the leads to the external D.C. switch terminals on the Sound Decay timer and put a jumper between these terminals. By disconnecting this jumper, the D.C. cu
17、rrent to the thyratrons is broken and the tubes will stop conducting, thereby resetting the circuit. Adjust the input signal to the desired level at which timing is to start and adjust the COARSE and FINE starting attenuators to the point where the clock will start. This may be best done by starting
18、 well up on the attenuator and slowly retard the controls until the clock starts. FORD LABORATORY TEST METHOD BV 003-04 Page 3 of 11 Copyright 2000, Ford Global Technologies, Inc. Next adjust the input signal to the desired level where timing is to end and adjust the STOP attenuator controls in the
19、same manner. The meter on the Sound Decay Timer is used to indicate the regulated D.C. voltage of the power supply and the negative bias voltage applied to the two thyratrons. Conditioning and Test Conditions All test values indicated herein are based on material conditioned in a controlled atmosphe
20、re of 23 +/- 2 C and 50 +/- 5 % relative humidity for not less than 24 h prior to testing and tested under the same conditions unless otherwise specified. Procedure 1. Assemble equipment as shown in Figure 1. Measurements are made with the Sound Decay Timer. The material is placed or sprayed on the
21、steel panel. The panel, supported on its nodal line, is set in vibration electrically. After the source of vibration is stopped, the time required for 30 db of sound decay is measured in seconds. The 30 db divided by the time is the Vibration Decay Rate in db/second. 2. Calibrate steel panels. The l
22、ocation of the nodal pattern of the plate is determined by placing fine dry sand in the center of the panel and the panel is excited at its resonant frequency. A pattern similar to that shown in Photograph 1 will be formed. The node line is the part of the plate which has the least tendency to vibra
23、te regardless of the amplitude of the vibration. 3. Coat with mastic sealer, bake and prepare the steel panels as required by the Engineering specification. With preformed material, lay 20 x 20 inch piece on steel plate. Support the steel plate at four points on the node line. Adjust four mounts so
24、that test panel is approximately 1/16 inch above magnetic driver. 4. Tune the audio oscillator to the resonant frequency. (Approximately 160 c.p.s.). The plate will vibrate with an intensity depending upon the amount of energy applied, the gap between magnetic driver and test panel, and the type of
25、deadening material fastened to the test panel. 5. Remove the excitation by turning off the exciter unit and allow amplitude of vibrations to decrease to zero. Read from timer the interval between the two predetermined points on the decay curve over a maximum of about 60 db range. Because of the load
26、ing effect when a deadening material is applied to the plate, the exciter unit is not capable of driving the plate to the full 60 db range. In this case, evaluate about 30 db. Make readings at all temperatures required in the material specification. Chemicals, materials, parts, and equipment referen
27、ced in this document must be used and handled properly. Each party is responsible for determining proper use and handling in its facilities. FORD LABORATORY TEST METHOD BV 003-04 Page 4 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-0
28、4 Page 5 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 6 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 7 of 11 Copyright 2000, Ford Global Technologie
29、s, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 8 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 9 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 10 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST FORD LABORATORY TEST METHOD BV 003-04 Page 11 of 11 Copyright 2000, Ford Global Technologies, Inc. VIBRATION DAMPENING TEST
