Table of Contents
Advertisement
18
The Accelerometer Calibrator Type 4291 is a small vibration exciter driven by a built-in
generator and powered by internal batteries. See Fig.4.2.
The Accelerometer to be calibrated is fixed to the instrument's vibrating table, which can
be adjusted to vibrate the accelerometer at 500 rads.
sec-
1 (79,6 Hz) with a level of
10m. sec-
2
(peak sinewave value).
The procedure is as follows
:
1.
Connect the accelerometer cable to the Preamplifier Type 2642 using the adaptor
JJ
2615 as in Section 3.3.2. Ensure that the Preamplifier is plugged into the INPUT
socket of the 2116.
2.
Ascertain the mass of the Accelerometer from its calibration chart.
3
.
Mount the Accelerometer (finger-tight is sufficient) to the table by means of a
10-32 UNF stud. For accelerometers having a 3 mm stud, use the 3 mm-to-1 0-32
UNF adaptor (DB 1425). For accelerometers not having a stud or tapped hole, use
the cementing stud (DB 0756) and wax or cement
.
4.
If the internal battery supply of the 4291 is to be used, switch the FUNCTION SE-
LECTOR to
"Batt.
Check"
.
If the METER deflection falls outside the green
"BATI ."
mark, replace the batteries.
5.
Switch the FUNCTION SELECTOR to "Internal Gen." The Calibrator will now vibrate
the accelerometer at 79,6 Hz (i.e. 500 radians
/
second)
.
6.
Adjust the ACC. LEVEL control until the METER pointer coincides with the load
mass on the
"0
... 1 00 gram" scale. The load mass is the total mass attached to
the vibration system, usually the accelerometer to be calibrated and the mounting-
stud (the latter is generally negligible). The accelerometer is now subjected to a sinu-
soidal acceleration of 10,0 ms-
2
peak
±2%.
DATE
_
__
_ _
~
OffRATOR
______________________
_
HEARING AID
TYPE
- - - - - - - - - - - - -
-- - -
-- - - - - - - - - - -
REMARKS
____________________________________________
__
dB
16
25
~
140
i
i
90
-
I
I
r----
B5
130
f - -
:
r-
124
dB
80
I
j
~
120
75
~
INPUT
SPL
I
I
Cahbrate
f - -
110
65
I
I
r----
60
100
r----
I
I
-
94dB
~
L C
MODE
90
-10ms-
2
~
-
I
I
Calibration
level
~
BO
from 4291
I
I
HARMONIC
{
2nd
70
1---
I
I
3rd
60
1---
I
I
INTERMODULATION
{
2nd
50
f - -
3rd
I
I
I
40
102
Vibration
Level
(ms-
2)
10
1Q-1
1Q-2
0,125
0,250
0,5
B
kHz
QP0009
0
0
BrUe
l
&
Kjcer
Ncerum
,
Denmark
D O +
790349
Fig.4.3.
Direct vibration calibration of the recording chart in ms
-2
using Accelerometer Calibrator Type 4291
Advertisement
Table of Contents
