CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
IMPROVEMENTS IN THE SIGNAL FIDELITY OF THE MANGANIN
STRESS GAUGE
Dan Greenwood, Jerry Forbes, Frank Garcia, Kevin Vandersall, Paul Urtiew,
LeRoy Green and Leroy Erickson
Lawrence Livermore National Laboratory,
P.O. Box 808, L-283 Livermore CA 94551.
Abstract: The manganin stress gauge has been and still is the primary diagnostic tool for
measuring longitudinal stresses in materials shocked from 10 to 400 kb in one-dimensional (ID)
uniaxial strain experiments [1]. Its simple and robust design allows this gauge to survive in harsh
environments. The manganin gauge has several limitations. For example, in the eventual failure
mode, the manganin gauge has a reputation of being a noise generator to the remaining functioning
manganin gauges at different lagrangian positions in the experiment. The manganin gauge also
demonstrates undesirable signal effects when the front edge of the incoming shock first makes
contact. These two limitations and the experiments for the mediation of these effects on shock
experiments will be presented in this paper. Our ultimate goal is to provide practical manganin
gauging that has true fast rise time and little or no noise generation on failure in explosive
detonation waves. A device was found that mitigates the noise generation without compromising the
integrity of the pressure data.
INTRODUCTION
element. A pulsed constant current, typically 50 A,
power supply is used to excite the gauge element.
The voltage change due to the piezoresistive effect
is measured on separate sense leads using highspeed digitizers.
One goal is to provide nose mitigation due to the
gauges failing with minimum gauge redesign. This
minimum gauge redesign is necessary because of
the extensive history and data base generated using
this gauge design [1]. The standard Livermore
manganin gauge [2] is shown in Fig. 1. It has a
nominal thickness of 0.025 mm. The gauge is a
peizoresistive device with the active element being
nominal 50 mflL It uses a four-wire (Kelvin)
method for measuring resistance change in the
Figure 2 reveals where potential noise problems
exist. The manganin gauge leads form two loops
and these loops are susceptible to pickup from
otherloops (i.e. manganin gauges) in the experiment.
These loops have a nominal 50 nH (calculated and
measured) of inductance along with a small amount
of stray capacitance 4.25e-14F (calculated) for a
55 mm long gauge.
Active Area
The RG 58 coax cable has an inductance of
1.2 uH. At 50 A excitation current the stored energy
in the RG 58 and gauge current loop is 1.51 ml. The
excitation power supply has an open circuit voltage
of 350 V. During the experiment the current leg
often opens in the nanosec time frame. This causes
the small magnetic field in the gauge to collapse and
FIGURE 1: LLNL Manganin Gauge
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Digitizer
50Q Signal Cable
Manganin
350 Volt
50 Amp Pulsed
Power Supply
Gauge
19'RG 58 Coax
Zo=50Q
Mductance=1.2 uH
Energy @ 50Amps = 1.2 mJ
livermore Gauge
Inductance 50 nH
Capacitance .043 pF
Stored Energy @ 50 Amps=6.25uJ
FIGURE 2. Manganin Gauge Electrical Circuit
the RG 58 transmission line to go from a shorted
condition to open and reflect a large amplitude wave
down both legs of the manganin gauge. This wave is
not terminated at the power supply and gets
reflected back to the gauge. This mismatch along
with the open end of the manganin gauge can cause
data disturbance in the other functioning gauges all
from a few hundred nanosecs to over a microsec
time duration. For the coax/current loop to dissipate
the energy in that period, it would be between 1.5 to
7.5 kW.
were placed at two
explosive/Lucite interface.
distances from
the
Our testing sequence started with a base line
experiment of the noise for a typical or standard
gauge setup without any noise abatement devices
(i e. circuit protection). We then conducted
experiments to reduce or eliminate the noise sources
( i e. ground loops, capacitance in the power supply
and common mode rejection). These experiments
provided with good noise records but very little in
the way of noise reduction when gauge breakage
occurred. Figure 4 shows a set of experiments that
have varying gauge cross talk as the gauges break.
The red traces show noise pickup from the previous
gauges (noise donors not shown). The blue and
green traces show noise reduction from the breakage
of the noise donor gauges.
EXPERIMENTAL PROCEDURE
To economically test various devices for this work,
small scale explosive tests were used (see Fig. 3).
These had 2.54 cm diameter right cylindrical pellets
of explosives which sent strong shock waves into
2.54 cm diameter by 5 to 10 mm thick Lucite disks
with manganin gauges between these disks. Gauges
Looking for a suitable shunting device was a
parametric search. The shunting device had to be
fast to match the rapid opening of the gauge and
have low parasitic capacitance so the signal integrity
was not affected. It also had to absorb the fault
energy.
Current shunting devices were tried. These
devices are attached to the current leg of the
manganin gauge and act as an open circuit until the
gauge breaks. The shunt device conducts in the
nanosecond time frame and carries the current
intended for the gauge. The drawback on most
semiconductor shunt devices is there high parasitic
capacitance, which causes the signal to ring.
FIGURE 3. Typical Noise Test Bed Experiment
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FIGURE 4. Normalized Data. Red Traces without Shunt, Blue
and Green Traces with Shunt
FIGURE 5. Transient Suppressor Wired to Manganin Gauge
Semiconductor and polymer based devices with
small junction capacitance were also tried but they
could not absorb the energy without failing in the
time frame of importance. In addition, a low voltage
gas discharge tube from CP Clare has low
capacitance but it is noisy when it turns on.
of the gauge response. It was also discovered that
the gauge leads are susceptible to the incoming
shock and will disturb the front edge of the
manganin foil gauge record. Although not shown in
this paper, the noise-mitigating device has worked
well on gun experiments using multiple gauges at
different depths in the explosive targets.
A small electrostatic discharge protection device
was found that fit the requirements. It is normally
used in protection of Input Output (I/O) lines on
computers (high speed, low capacitance). The
device is made by Semtech and is called LCDA15.
It is a four-device array of transient suppression
diodes.
ACKNOWLEDGEMENTS
Gary Steinhour, Ernie Urquidez and Denise
Grimsley assisted on the experiments. Douglas
Tasker (LANL) gave advise on noise mitigation for
gauge circuits. We are saddened to announce the
loss of our colleague Leroy Erickson. This work
was performed under the auspices of the United
States Department of Energy by the Lawrence
Livermore National Laboratory under contract No.
W-7405-ENG-48.
One of the four diodes was used per gauge in our
experiments. The results show major reduction of
noise from gauge breakage. The blue and green
traces in Figure 4 shows a typical LCDA15 coupled
with a manganin gauges. The red traces also show
gauge records without shunt devices. Figure 5 is a
photograph of the transient device soldered to the
manganin gauge leads
REFERENCES
1. Vantine, H. C, Erickson, L.M, and Janzen, J., "
Hysteresis-Corrected Calibration of Manganin under
Shock Loading," J. Appl. Phys., 51(4), pp. 1957-1962.
(1980).
2. Vantine H, Chan I, Erickson L. M, Janzen I, Lee R
and Weingart R. C., "Precision Stress Measurements in
Severe Shock-Wave Environments with Low Itnpedance
Manganin Gauges," Rev. Sti. Lnstr., 51: 116-122, (1980).
SUMMARY
We have examined the cause of the noise
disturbance due to gauge breakage in shock wave
experiments. A device was found that mitigates the
noise generation without compromising the integrity
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