Pressure transducer

A pressure transducer has at least one pressure transmitting space filled with liquid, a space for a pressure to be sensed connected to the pressure transmitting space through a diaphragm, and a pressure sensitive element in the pressure transmitting space for transducing a pressure transmitted from the space for the pressure to be sensed to the pressure transmitting space through the diaphragm to an electrical signal. A printed circuit board wired to electrically connect terminals of the pressure sensitive element is arranged closely to the element and thin temperature sensitive elements for temperature-compensating the pressure sensitive element are arranged on the printed circuit board.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates a pressure transducer for sensing a pressure 
or a differential pressure, and more particularly to a pressure transducer 
which introduces a pressure in a space for a pressure to be sensed to a 
pressure transmitting space through a diaphragm and senses the pressure in 
the space for the pressure to be sensed by a pressure sensitive element 
disposed in the pressure transmitting space. 
2. Description of the Prior Art 
The pressure transducer of the type described above transduces the pressure 
in the pressure transmitting space to a mechanical strain, which is then 
transduced to an electrical quantity, and it usually uses a vapor 
deposition type strain gauge or a diffusion type strain gauge. The 
diffusion type strain gauge is manufactured by diffusing impurity into a 
silicon base diaphragm, and it is commonly referred to as a semiconductor 
strain gauge. Since the semiconductor strain gauge has much higher gauge 
rate than a wire strain gauge, it is widely used in the field of pressure 
sensing. However, since the semiconductor strain gauge is highly 
influenced by a temperature, a temperature compensation is needed. For the 
temperature compensation, it is advisable to arrange a temperature 
sensitive element such as a thermistor closely to the semiconductor strain 
gauge. On the other hand, since the pressure transmitting space is filled 
with liquid such as silicone oil, it is necessary to prevent the change of 
volume of the liquid by temperature change from affecting to the pressure 
in the pressure transmitting space. To this end, the volume of the space 
is designed as small as possible. 
The arrangement of electric components such as temperature sensitive 
element in the pressure transmitting space results in the increase of the 
volume of the pressure transmitting space because a space for means for 
holding the electric components is necessary in addition to a space for 
the electric components. Heretofore, the electric components have been 
arranged outside the space through a hermetic seal. Since the temperature 
sensitive element must be located at a position which is subjected to the 
same temperature as the pressure sensitive element is subjected to, it has 
been disposed as closely to the pressure sensitive element as possible 
outside the pressure transmitting space. 
Recently, higher presision has been required for the pressure transducer. 
Where the temperature sensitive element is spaced from the pressure 
sensitive element by other members like in the prior art transducer, a 
high precision pressure transducer is not attained because of a 
temperature difference between both elements due to temperature change in 
the space for the pressure to be sensed or change of surrounding 
temperature. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a pressure transducer 
which is constructed to enable the close arrangement of the temperature 
sensitive element and the pressure sensitive element within a common 
space. 
According to the present invention, a printed circuit board having a wiring 
pattern to be connected with wiring pads of the pressure sensitive element 
is arranged closely to the pressure sensitive element, and thin 
temperature sensitive elements are arranged to the printed circuit board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, a pressure transducer in accordance with the present 
invention mainly comprises a housing 10, a cylindrical support 12 and 
flanges 14 and 16. The housing 10 has a generally rectangular periphery 
and a center portion including a cylindrical inner wall 18 and a bottom 22 
having a step 20. The support 12 is mounted on the step 20 with a space 24 
being formed between the peripheral surface of the support 12 and the 
inner wall 18 of the housing 10. A plurality of radially extending grooves 
26 are formed in the bottom of the support 12 to communicate the space 24 
with a space 28 above the bottom 22. 
Mounted on the support 12 is a connecting member 30, and junction on 
circumferential walls of the support 12 and the member 30 is welded over 
the entire circumference. A space 32 is defined between the top surface of 
the support 12 and the connecting member 30, and the space 32 communicates 
with the space 24 through a via-hole 34 formed in the connecting member 
30. A cylindrical member 36 is mounted on the connecting member 30 and 
both members are welded together along circumferential junction. A case 
for accomodating electric components is attached to the cylindrical member 
36 by a female screw 38. The interior of the case is sealed by an O-ring 
disposed in a ring groove 40. 
Rectangular flanges 14 and 16 are clamped to both sides of the housing 10 
at their corners by bolts 42 and nuts 44. The flanges 14 and 16 have 
connecting threads 46 and 48, respectively, on inner circumferential 
surfaces of via-holes for connecting conduits, not shown, extending to the 
space for the pressure to be sensed. Sealing packings 50 and 52 are 
arranged between the housing 10 and the flanges 14 and 16, respectively. 
Seal diaphragms 58 and 60 are attached, by tig welding, to inner walls of 
ring projections 54 and 56 on the support 12 which fit to the flanges 14 
and 16. The space 24 is divided into two spaces by an O-ring 62. Each 
space is filled with silicone oil, which is charged to the seal diaphragm 
58 or 60 through hole 64 or 66. 
A via-hole having two steps is formed at the center of the support 12 made 
of steel, and a cylindrical holder 68 made of iron-nickel alloy or 
iron-nickel-cobalt alloy is welded to the smallest diameter portion at the 
top of the via-hole, and a ring interposer 70 made of glass is attached to 
the bottom of the holder 68 in liquid tight manner, and a pressure 
sensitive element 72 made of semiconductor such as silicon and having a 
diaphragm 74 at the center thereof is attached to the bottom of the 
interposer 70 in liquid tight manner. 
Thermal expansion coefficients of the cylindrical holder 68 and the 
interposer 70 are selected to be intermediate thermal expassion 
coefficients of the holder 12 and the pressure sensitive element 72, with 
the thermal expansion coefficient of the holder 68 being closer to that of 
holder 12 than that of the interposer 70. By this arrangement, a strain to 
the pressure sensitive element due to temperature change is minimized. A 
pressure applied to the diaphragm 58 is applied to the upper surface of 
the diaphragm 74 through the via-hole 64, the via-hole 34, the space 32 
and the central bores of the cylindrical holder 68 and the interposer 70. 
On the other hand, a pressure applied to the diaphragm 60 is applied to 
the lower surface of the diaphragm 74 through the via-hole 66 and the 
groove 26. Consequently, the diaphragm 74 produces a strain which is 
proportional to a differential pressure. 
Impurities have been diffused at a plurality of areas on the lower surface 
of the diaphragm 74 to construct a semiconductor strain gauge. A 
doughnut-shaped ceramic printed circuit board 76 is mounted on the lower 
surface of the holder 12. It is solder-bonded to conductors 80 which 
extend through thirteen via-holes 78 extending along center axis of the 
support 12 on a common circumference. The conductors 80 are supported by 
hermetic seals 82 disposed in the via-holes. The lower surface of the 
printed circuit board 76 is positioned at a substantially same level as 
the lower surface of the diaphragm 74. 
As shown in FIG. 2, the printed circuit board 76 carries printed wiring 
which includes thirteen soldering printed pads 84 along a common 
circumference. Those pads 84 are solder-bonded to the conductors 80 
extending through the hermetic seal 82. The printed circuit boards 76 
further has three thick film thermistors 86 printed and baked with the 
wiring pattern. The thermistors may be of thin film, vapor deposition type 
or thin plate, bonded type. The wiring pattern includes ten bonding pads 
88 to be connected with wiring pads of the pressure sensitive element 72. 
The wiring pads of the pressure sensitive element 72 and the bonding pads 
88 are connected together through ultrasonic wave bonded leads 90. By 
positioning the lower surface of the printed circuit board 76 at the 
substantially same level as the lower surface of the pressure sensitive 
element 72, the welding work of the leads 90 is facilitated and the space 
28 can be reduced. 
The conductors 80 extending through the hermetic seal 82 have their copper 
ends connected to wiring pattern of a flexible printed circuit board 92, 
which is folded back into a generally disk shape. Wiring pattern on the 
upper plate and wiring pattern on the lower plate are electrically 
interconnected at folding portion. The lower plate of the printed circuit 
board 92 is held on the conductors 80 by connecting the wiring pattern on 
the lower plate to the conductors 80 while leaving a space from the upper 
surface of the support 12. Thus, the space 32 communicates with the center 
bore of the cylindrical holder 68 through the space between the lower 
plate of the printed circuit board 92 and the holder 12. The upper plate 
of the printed circuit boards 92 is held on a plurality of conductors 94 
by connecting the wiring pattern on the upper plate to the conductors 94, 
which extend through a hermetic seal 96 and thirteen via-holes formed in 
the connecting member 30 on a common circumference. The conductors 94 are 
connected to an electrical circuit accomodated in a case fixed to the 
cylindrical member 36. 
According to the present invention, input pressures to be sensed are 
received at the flange 14 and the flange 16. Thus, a differential pressure 
therebetween may be sensed, or one pressure may be used as a reference 
pressure to measure the other pressure. In the latter case, the reference 
pressure port may be opened to an atmosphere or it may be connected to a 
predetermined pressure source. 
Furthermore, according to the present invention, the pressure to be sensed 
may be a pressure derived from transducing a weight of article to the 
pressure. In this case, a weight transducer is provided.