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Vibration of a gram-atic balance and industrial camera
Pernica, G.
NATIONAL RESEARCH COUNCIL OF CANADA
No.
DIVISION OF BUILDING RESEARCH
582
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ｾ ｾｪ ｾ［＼ＺＱ' . J .PREPARED BY Gerald Pernica CHECKED BY TDN APPROVED BY CBC
PREPARED FOR Record Purposes
ｄａｾｅ June 1974
SUBJECT VIBRATIONS OF A GRAM-ATIC BALANCE AND INDUSTRIAL CAMERA!
A. IIGRAM-ATIC" BALANCE
Vibration measurements were taken on 27 February 1973 at the Microsystems International Building in Bells Corners Ontario which is located just west of the City of Ottawa. Difficulty was experienced in ob-taining a clear image on the screen of a GRAM-ATIC Balance. This type of balance has a sensitivity of 0.0001 gm. The instrument rested on a stone bench in one of the chemistry laboratories situated on the main floor of the building (Fig. 1). It had been isolated from the floor by placing one 3 in. by 1-1/2 in. pad of IIFabcel 100", a rubber material, under each of its corners (Fig. 2 and 3).
A great deal of mechanical equipment was located in the immediate vicinity of the chemistry laboratory (Fig. 1). The room on one side of the chemistry laboratory contained seven 40 hp compressors, four aligned in the north-south direction, and three in the east-west direction. Those in the north-south direction had an rpm of 3500 while those in the east-west an rpm of 3505. At the time the vibration measurements were taken four compres sors were on, two in each direction.
A large two-storey mechanical room was located at the rear of the chemistry laboratory. The floor of this room was one storey below that of the laboratory. Several large pumps were amongst the many pieces of equipment in this room. The number of pumps and other mechanical
2
-equipment that were operating at the time of the vibration measurements was not known.
Meas ure ments
The vibration measurements were made with a "Larson" accel-erometer. The output from the accelerometer was recorded on a Century Strip Chart recorder. For each measurement four seconds of output were recorded.
A scan of the floor and existing bench vibrations revealed that the amplitudes in the vertical directions were approximately five times as large as those in the horizontal. Consequently, only vertical records were examined in detail.
Vertical vibrations were measured on the bench and on the floor beside it. Different isolation patterns were used beneath the bench em-ploying Fabcel 100 as the isolator. For each measurement the output from the accelerometer was filtered to pass only those frequencies with-in the 0-90 Hz band. This frequency band contained the lowest dominant frequency present in each of the records.
Results
The results of the tests are given in Table I. It can be seen from the results that the original isolation system (Test No.2)
had actually amplified the vertical floor vibrations. With the addition of an extra layer of Fabcel 100 (Test No.3 or Test No.6) the vertical vibrations of the bench were reduced to approximately one-fourth of
those existing on the floor. This level of bench vibration no longer inter-fered with the operation of the balance and was therefore considered satisfactory.
B. INDUSTRIAL CAMERA
Additional vibration measurements were taken in a room which housed a special camera used for the reduction of etching circuit diagrams. This unit is shown in Figs. 4 and 5. The unit was isolated from the floor by four air mounts, two at each end. The air supply to all four mounts is interconnected so that each mount has the same pressure. At the time measurements were taken the pressure in each of the mounts was 80 psi.
No vibration problem had as yet occurred during the operation of this unit. However, the unit had not yet been used to its fullest reduction capacity. As this capacity was soon to be realized, a knowledge of the existing vibration levels was desirable.
3
-A scan of the floor and camera unit vibrations revealed that those in the horizontal directions were much less than those in the vertical. Therefore no further horizontal records were taken. Vertical vibration measurements were taken on the camera unit under normal operating conditions and under human excitation. The latter condition was em-ployed in order to determine the lowest natural frequency of the camera unit. For each measurement the output from the accelerometer was filtered to pass those frequencies within the 0-90 Hz band.
Results
The results of the ambient vibration measurements are given in Table 2. No discernible dominant frequency was present in any of the records.
The lowest natural frequency of the camera unit was approximately 4 Hz. Whether this was a pure translational, rotational or rotary mode, or a mixture could not be determined from the existing data.
It can be seen from Table II that the air mounts did not reduce existing floor vibrations. However, they should provide isolation from floor vibrations caused by door closings, footsteps, mechanical equip-ment, etc., because of the low fundamental frequency of the camera unit. No measurements were taken to confirm this.
TABLE I
VIBRATION MEASUREMENTS: CHEMISTRY LABORATORY
On Floor
On Bench Type of Is olation
Beside Bench
Test For Bench
No. Lowest Amplitude'l< Lowest Amplitude>:< Ratio Using Fabcel 100
Dominant Dominant Bench to Pads
Frequency 10-3 g Frequency 10- 3 g Floor Hz Hz Amplitudes 1 59 7.8
2 60 27.0 3.5 one 3 x Ii - in. pad
at each corner
3 60 2.0 0.3 two 3 x 18-in. pads
each side
one 3 x Ii-in. pad at each corner
4 60 16.0 2. 1 one 3 x 3-in. pad
at each corner
5 61 5. 2 0.7 two 3 x 3-in. pads
at each corner
6 61 2.0 0.3 two 3 x 3-in. pads
at each corner one 3 xli- in. pad at each corner
TABLE II
VIBRATION MEASUREMENTS: CAMERA ROOM
On Floor On Unit
Location Amplitude >:< Amplitude
-'--,-10- 3 g 10- 3 g
At Camera 1.6 2.0
At Screen 1.4 1.2
N - - . . 1 ｾ TWO-STOREY / - - - MECHANICAL
o
COVERED r--r---t
D RA INS II ROOM ---lBLOC K WA LL INTERIOR PARTITIO N _ S TO N E BENCH-D ...J <t: V Z <t: :I: V ｕｊｾ ｾｏ 00 t- '"ｬｾ
I t-to.,...--te-itC 0 M PRE SS0 RS COVERED ｄｒａｉｎｾ I Ｍ｟ＮＮｊｴｾ］ｾｃｏｍｐ RE SSO RS t _ ....ｮｾ _ _ '-... ....L..J. " ' - ....I HALLWAY LOCKER AREA FIGURE 1PLAN VIEW OF CHEMISTRY LABORATORY AND
ENVIRONS
o
BALANCE
ｾｬ
....: U-N ｾ Ｓｾ APPROX. 2 1/2 FT. 3 IN. N x 0 e>: 0.. 0.. FABCEL 100 «-
---
--
I .-FIGURE 2 FRONT VIEW OF BENCH
BALANCE
---APPROX. I 1/2 FT. I ｉｾ I 1/2 IN.t'
·1
--
•
•
e
•
I--SCREEN
II I MATERIAL FOR ISOLATION
OF SCREEN FROM REAR
SUPPORT
