The standard carbon composition resistors 
were found to change very radically with the 
application of pressure. Figure 3 summarizes 
the behavior of 100 to 10,000,000-ohm resistors 
under the same hydrostatic pressure environ- 
ments (10,000 psig). Because of their marked 
sensitivity to pressure change, composition 
carbon resistors appeared attractive for use as 
pressure transducers, 
CAPACITORS 
A number of capacitors (molded mica, 
ceramic disk, glass, and paper) have undergone 
tests to 10,000 psig. All of these capacitors 
worked satisfactorily under the high pressure 
and suffered no damage, The molded mica and 
glass types showed no appreciable change in 
capacitance with varying pressure, Some ce- 
ramic types showed changes in capacitance of 
as much as two per cent but no effort was made 
to test all the types now available, Paper 
capacitors selected were mainly of the minia- 
ture types, in which size reduction had been 
accomplished by such methods as depositing 
the conductor directly on the dielectric. These 
miniature capacitors also are usually impreg- 
nated with wax and carefully treated to exclude 
all air bubbles, Surprisingly enough, these 
miniature types withstood the pressure and 
showed very little change in capacitance, 
Changes in the range of 1% were common with 
this type of capacitor, 
Capacitors sealed with air entrapped were 
not satisfactory for use under hydrostatic 
pressure; an example of such a capacitor is 
shown in Figure 5, Electrolytic capacitors 
frequently contain a considerable amount of 
void space and consequently collapse ata 
relatively low pressure, These units usually 
are operable at reduced voltages even after 
collapse, Some types of paper capacitors are 
inserted into a paper tube and sealed by pour- 
ing wax or plastic compound into the end of the 
tube, Such capacitors usually contain entrapped 
air and collapse at a relatively low pressure, 
There appears to be no problem at this 
time in selecting capacitors to meet the 
common electronic circuit requirements and 
to operate under hydrostatic pressures up to 
10,000 psig. 
120 
MAGNETIC MATERIALS 
Measurements of various magnetic ma- 
terials were conducted by subjecting coils 
wound on various types of magnetic cores to 
hydrostatic pressures as high as 10,000 psig 
and measuring the inductance as the pressure 
was varied. The magnetic materials tested 
were some of those commonly used in elec- 
tronic circuits for instruments of various 
types. The materials tested were: 
1. Grain oriented silicon steel 
2. 75% nickel-iron 
3. 50% nickel-iron 
4. Powdered iron (high-frequency 
formulation) 
5. Powdered iron (low-frequency 
formulation) 
6. Powdered iron (medium frequency 
formulation) 
7. Molybdenum-nickel-iron dust core 
8 Ferrite core. 
The grain-oriented silicon core was of the 
split-rectangle type, while all other cores were 
torodial and approximately 1 inch in outside 
diameter, In all measurements the frequency 
was 1000 cps. 
The most dramatic change observed was 
in the 50% nickel-iron core of the grain-ori- 
ented square-loop type. This core nearly 
doubled in inductance at a very low pressure 
as shown in Figure 4, It is interesting to 
note that after the change occurred, further 
changes in pressure had very little effect on 
the inductance, Changes observed in the other 
types were less dramatic, but the grain-ori- 
ented silicon core was interesting in that it 
was the only type tested which exhibited a 
large decrease in inductance as the pressure 
increased, The total change observed was 
about 14% (negative), but the residual effect 
was a slight positive inductance change, The 
molybdenum-nickel-iron cores exhibited a 
change of about the same amount but in the 
opposite direction, 
Inductors using the powdered iron and the 
75% nickel-iron cores were found to exhibit 
inductance changes of less than 5% as the 
hydrostatic pressure was cycled between 
atmospheric pressure and 10,000 psig, as 
shown in Figure 5. The inductors wound on 
the powdered iron cores showed an increase 
in inductance with increased pressure, The 
