Figure 86. Teat instrumentation.
transducer selected while the amplifier
may be the same for all transducers
An electric primer, such as the M52A3, is
although a piezoelectric gage requires a
held in place in the firing head by the
special type (high-input impedance) of
primer retainer, maintaining contact
coupling stage.
between the contact on the head of the
primer and the contact pin. The firing
(5) A number-of transducers and amplifiers
head is inserted in the gas entry port of
are commercially available. Examples of
the device to be tested and the firing and
several types of transducers and an
ground cables are connected to the firing
amplifier are described in b through e
head. When the firing circuit is closed,
below.
As an aid in selecting a
current flows through the contact pin and
transducer, table XVI is presented. This
primer and ignites the charge contained in
table lists the possible calibration error (as
the primer. The gas produced by the
listed by the manufacturer) for several
primer operates the firing mechanisms of
types of transducers, and also lists the
the propellant actuated device being -
"possible total error" of measurement
tested. The universal firing head may
based on the assumption that a 2
also be used to operate an initiator which,
percent error may occur due to amplifiers,
in turn, fires the propellant actuated
oscilloscope or oscillograph, and other
device.
instrumentation, as well as errors in
observation. Furthermore, when using
b. Amplifiers and Recorders.
pressure gages to measure acceleration,
(1) The amplifying system used may be of
there may be errors in the assumed
any convenient type, i.e., direct coupled
relationship between pressure and
or carrier frequency type. The primary
acceleration, which may be arbitrarily set
requirement is that the amplifiers are kept
at 0.5 percent.
linear, free of drift, and properly
calibrated. An example of piezoelectric
Table XVI. Possible Errors Involved in Acceleration
amplifier with an input impedance of
Measurement
1,000 megohms or greater is shown in
Minimum
Minimum error
Transducers
calibration error
of measurement
(2) The recorder may be a combination of
(percent)
(percent)
oscilloscope and still camera or high
Piezoelectric gage ...........
0.5
3.0
Strain resistance pressure
gage ............................
1.0
3.5
Pressure pickup ...............
2.0
4.5
Load cell .........................
0.5
2.5
Accelerometer .................
1.7
3.7
(6) Propellant actuated devices generally are
fired electrically to synchronize the firing
with triggering of the associated
instrumentation. A universal firing head
using electrically fired primers has been
designed to be inserted in the gas entry
port of gas actuated firing mechanisms.
Figure 87. Universal electric firing head.
98
