Shure 61B, 62B User Guide

DATA SHEET No. 163A

DATE:

June 1942

SUBJECT:

MODELS 61B AND 62B VIBRATION PICKUPS

GENERAL:

brations in industrial fields. The piezoelectric ele­ment is a grafoil bimorph Rochelle salt crystal unit
with special-process moisture-proofing. The crystal
element is inertia actuated, which principle eliminates

the need of a stationary reference body in vibration
measurements. The isolated mounting used in this type
of actuation gives a maximum protection against break­age of the crystal. The assembly is enclosed in a

cast aluminum case.

The output voltage Is proportional to the vibra­tion due to acceleration throughout the linear range
of the instruments, giving a relative measure of the

stresses set up by the vibratory motion. Model 61B
has a linear voltage-acceleration characteristic up to
approximately 1000 cycles per second, a frequency
range which is suitable for general vibration studies.
Model 62B has a voltage output about four times that
of the 61B and a linear characteristic extending to
500 cycles per second. The latter model is recommended
for applications such as the direct energizing of
headphones or oscilloscopes, which require a relative­ly high output voltage. Both instruments are respon­sive beyond the linear range, to frequencies up to
approximately 3000 cycles per second. Modification of
the frequency characteristics is possible through use
of simple circuits,
flexibility of the devices.

Each instrument is equipped with a complete set
of adapters Including an extension rod, ball-tip,
point-tip, and mounting bracket.

APPLICATIONS :

sign, inspection, and In many other fields. Some of
these applications are suggested below:

Industrial Research and Design: Determination of
optimum shapes and material distribution in high-speed

rotating members, motor windings, and hydraulic equip­ment. Research in vibration isolation materials, con­struction of vibration-proof rooms, vault protective
systems, etc. Noise reduction of automobile and air­plane structures, gearing, bearings, etc.

Manufacturing and Inspection: Balancing of ro­tors, adjustment of gears and impact devices, uni­formity of air-gap pull, smoothness of surfaces; vi­bration in machinery, building structures, transmission
lines, antenna towers, etc.

Servicing and Surveying: Location and elimina-

tion of sources of vibration, loose pistons and bear-

ings; servicing refrigerators and air-conditioning

systems; isolation of machinery, tracing leaks in
water-pipes, tanks, and hydraulic structures, geodetic
surveying for oil and mineral strata, etc.

INSTALLATION:

pickup shank. Wherever it can be used conveniently,
the screw itself will give sufficient support. Other

accessories included am a ball-tip, point-tip, and 8"
Copyright 1938, Shure Brothers, Chicago

Models 61B and 62B Vibration Pickups
are piezoelectric instruments for
the measurement and analysis of vi-

extension rod. Special. setups for production testing
may be easily constructed, but care should be taken to

resulting In a greatly increased

Models 61B and 62B Vibration Pickups
have innumerable applications in

scientific research, industrial de-

Each pickup is equipped with a sta-

tionary mounting bracket and a screw
for the 1/4" - 28 thread in the

transmit vibrations approximately along the axis of
the pickup shank.

ductor rubber-jacketed shielded cable. If necessary,
the length of cable can be increased considerably
without excessive output loss. Low-capacity high in­sulation-resistance shielded cable should be used.
Shielded crystal microphone cable having a capacity of
25 to 50 micromicrofarads per foot, and a leakage
resistance of 200 megohm-feet of more, is recom­mended. All joints should be well-shielded to avoid
hum pickup.

but the cable connector box, while reasonably moisture-

proof, will not withstand immersion in water. (For
underwater work specially constructed Instruments are
available). The pickup should not be subjected to ex­tremely violent shocks or vibrations, nor allowed to
attain temperatures in excess of 125° F (51.7° C).
Extension rods of sufficient length will usually per­mit low operating temperatures near hot machinery.

CORNECTIONS:

or more. The green-coded conductor should be con­nected to the "high" or grid side of the amplifier
input, and the shield (black conductor) should be
connected to the ground or chassis of the amplifier:

(See Fig. 2).

high as 20 volts or more when measuring vibrations of

large amplitude. Under such circumstances, the device
should not be connected directly to the grid of the
tube without the use of a volume control or some other

type of voltage divider. A convenient way to attenu­ate the output voltage and avoid tube overloading is
to shunt the pickup terminals with a condenser as in­dicated by the dotted lines in Fig. 2. A 0.05 micro­farad shunt condenser will usually reduce the peak

Fig. 1. Illustration of Models 61B and 62B

Each instrument is provided with a 7' single con-

The crystal enclosure is entirely water-tight,

The full output of the pickup may reach peaks as

Models 61B and 62B

Vibration Pickups

Vibration Pickups and accessories.

(Approximately 1/3 actual size)

The pickup should be connected to
the grid circuit of a vacuum tube
across a load resistance of ½ megohm

No. 163

DATA SHEET

Fig. 2.

voltages to a safe value without affecting the fre-

quency characteristic. In measuring vibrations of

moderate amplitudes, this precaution may not be neces-

sary.

For most applications, a low or medium gain am­plifier will be satisfactory. The pickup may be very
conveniently connected directly to conventional type

cathode-ray oscilloscopes. In cases where the output

Is sufficiently high, the vibration pickup may be used
directly with high-impedance headphones, the crystal
type being especially suitable.

The use of transformers is not generally advis-

able in conjunction with crystal devices.

OPERATION:

used for point-to-point exploration, while the round-

tip is useful in checking surfaces for smoothness.

Remote parts of machinery may be reached through use

of the extension rod.

The maximum output of the pickup is obtained when

the direction of the displacement coincides with the

axis of the pickup shank. When the extension rod is
used,

ponent of vibration along the line of action of the
rod.

In hand exploration and test set-ups, only enough

pressure should be applied to the pickup to keep it

Recommended amplifier connection for

crystal vibration pickups.

firmly In place. Excessive pressure may alter the

amplitude of vibration observed and give erroneous

readings. The instrument should never be subjected
to exceptionally violent vibrations.

suggested operating arrangements of the pickup with
head-phones, oscilloscope, wave analyzer, or amplifier
and meter.
actuated crystal are in close relationship to the

stresses set up in vibrating bodies, the amplifier
meter readings will be roughly indicative of the aver­age vibrational stress. A calibrated cathode-ray

oscilloscope In conjunction with the pickup will serve
as a convenient means by which the values of vibra-

tional components may be estimated from visual ob-

servations.

In addition to permanent mounting

arrangements, the pickup may be held

in the hand. The point-tip may be

the readings obtained will represent the com-

temperatures exceeding 125° F. An extension rod of

sufficient length may be used to keep the pickup at a

safe distance from hot devices.

FREQUENCY
CHARACTERISTICS:

put of the 61B Pickup is very nearly proportional to
vibration acceleration up to approximately 1000 cycles
per second, and has a value of about 5 millivolts per

one-millionth inch total displacement at 250 cycles
per second. The voltage output of the 62B is approxi­mately 20 millivolts under the same conditions, and is
essentially proportional to acceleration up to about
500 cycles per second. The total frequency range of
both pickups extends to about 3000 cycles per second.

The block schematic diagrams of Fig. 3 give some

The instruments should not be allowed to attain

Fig. 3.

Suggested indicating arrangements

for vibration pickups.

Since the forces developed in the inertia-

Frequency response curves for con­stant amplitude vibration are shown
in Figs. 4 and 5. The voltage out-

Fig. 4.

proximately equivalent to that of a .005 microfarad

altered, depending upon the particular conditions. As
a general rule, frequencies above 1000 cycles per

problems, the effect or the rod is usually negli-

modified, if desired, by means of simple electrocal
networks described in the Appendix, page 3. In all

Typical frequency-response characteristics

of Model 61B Vibration Pickup.

(Applies to Fig. 2 without Condenser)

up.

The internal impedance of the instrument is ap-

condenser and hence the low frequency characteristic

is dependent upon the terminal resistance employed, as

Indicated in Figs. 4 and 5. The reduction in low-

frequency response obtained by connecting the pickup

to a low terminal resistance is a decided advantage in

some cases. For general applications, a terminal re-

sistance of 1-megohm is suitable. For studying very

low frequency vibrations, a 3 to 5 megohm termination

should be used.

When the pickup is used with the extension rod,

the actual motion transmitted to the pickup may be

second will be attenuated. Since frequecies below

1000 cycles per second predominate in industrial

gible.

Frequency characteristics of the pickup may be

cases, the complete circuit, Including the network

Itself, should be fully shielded to prevent hum pick-