type 4291

FEATURES: Internal batteries for portable, self-contained opera tion Stable, mechanically isolated vibration reference system Built-in velocity coil and suppressed-zero meter for p~ecise, easy adjustment to refelrence vibration level + 2% acceleration accuracy Reference level 1 O,O r n ~ - ~ acceleration, 20,O mms-I velocity, 40,Opm displacement Internal generator for standard 79,6 Hz (500 rad s--l ) operation

a Operates over 50 Hz to 2 kHz range with external generator

USES: QY ick, simple field calibration of all kinds of vibration measuring systems Acceleration, velocity and displacement calibration Easy calibration of accelerometer charge and voltage sensitivity Back-to-back calibration of vibration transducers for increased accuracy Insert-voltage calibration of accelerometers

Accelerometer Calibrator -. -

7

I Acesleromatar C a l i b r a t o r

L ----------. . , .---- - ---- L L L L L L L L 1 rwrcrtn~ rkt.umn . 1 1 1

Fig. 1. Electronics schsmatic diagram

The Accelerometer Calibrator It consists of a buift-in. stable Type 4291 provides a fully portable 79,6 Hz (500 fads-' ) sinusoidal vibration reference source for field generator, a compact electromag- and laboratory calibration of vibra- netic vibrator mechanically isolated tion measuring and monitoring sys- from the case. and a velocity-moni- terns and individual vibration trans- toring coil feeding a built-in measur- ducers, to a standard reference le- ina amolifier and meter. The meter ., .

Reciprocity calibration vel. has a suppressed electrical zero to

enable the reference level to be set up quickly and precisely with better than 0.5% resolution.

The basic method of system cali- bration with the 4291 is extremely simple. The vibration transducer of the system to be calibrated is fixed to the vibration table, which is con- veniently located in the centre of the front panel. The amplitude of the built-in generator is then ad- justed by means of a 10-turn knob, also on the front panel, until the me- t e r of the 4291 reads the mass of the transducer on its mass scale.

The table is then subjecting the transducer to a standard vibration acceleration level of 10,O rns -2 peak at 500 rad s - 1 (80 Hz approx. - DIN 45 666), which is equivalent to a velocity of 20,O mm s -1 peak and a displacement of 40pm peak.

The vibration measuring system to be calibrated is adjusted so that its output indicates whichever of these quantities is appropriate. Cali- bration for acceleration, velocity or displacement is thus equally simple.

The 4291 is also very convenient for establishing the voltage and charge sensitivity of accelerome- ters, and identifying performance degradation due to damage.

I 1 Fig.2. Cross-section new of the vibration system

In addition to the vibration table in the front panel, a second, similar table is provided, at the rear of the vibration system, for mounting a ref- erence accelerometer (see Fig.2).

Most internal connections are brought out to miniature coaxial sockets on the rear panel (see Fig.1). These facilities provide the flexibility needed for laboratory methods of transducer calibration such as the back-to-back and reci- procity methods. The Callbrator may

be powered from an external 22-28V supply, and driven by an external generator at frequencies in the range 50 Hz to 2 kHz, if re- quired. for back-to-back or reciproc- ity calibration.

The modular construction of the 4291 enables it to be used in its own case as a completely portable stand-alone unit, or in the B & K Modular Cassette system for 19" rack or field system use.

Specifications 429 1 Mechanical:

Width: 139.5 rnrn (6,5 in) Height: 132.6 mm (5,2 ~n) Depth: 200.0mrn (7,9 ~ n ) 18 & K Module Cabinet KK 0024, 4/12 of 19" rack module) Weight: 3.0kg (6.6 Ib)

Acceaaorisr Included: 4 alkaline batterbas 00 0004 1 threaded steel stud, 10-32UNF to M3, DB 1426 4 extra feet [for vertrcal posltloning) 1 vibration formula chart BR 0008

Aeeeesorie~ Availabla: Insert-voltaae adantor UA 0322

I Internal Generator:

Frequency: 79.6 i0.5 Hz (500 t3 rads-1) Peak amplitude, ref. to calibrated out- put: 10.0 t 0.2 rns -2 accelerat~on, 20,O i 0.5 mrns-1 veloc~ty, 40 f l ~ r n d~splacement (adjustable) Distortion: less than 1% (at tempera- tures htgher than 1 O0C)

Vibration System; Mounting connections for accelerome- ters: 10-32 UNF tapped holes Moving mean: 16 g approx. Max. stroke: * 1.5 mm displacement Transverse amplitude: less than 10% d main axis amplitude a1 79,6 Hz

Coilr: External frequency range: 50 Hz to 2 kHz

Max. input: 5VA continuous DC resistance: 70 13 epprox.

Temperature Range: -5' to +55OC 123' to 131 OF) 65 g load mass only to +4O0C

Hum Sensitivity: Negligible below 109Am -1

Power Source: Internal: 4 x 1 .5V dry cells, IEC Type R 20 IUD" size). B & K Type QB 0004 al- kaline cells (300 mA aoprax.) Battery lifetime: 20 hours intermittent E a s m ~ l : 22-28 \/ DC 140 mA aonrox.)

Erctrical connections: Mrniature coaxral sockets. accepting B & K Plug Type JP 001 2