Abstract:
An insulated IC pressure sensor comprises a main body, enclosing a chamber, having a hole for letting in fluid pressure of which is to be sensed, a pressure-sensing integrated circuit (IC), placed inside the chamber, and a membrane, placed inside the chamber between the hole and the pressure-sensing IC, tightly sealing the pressure-sensing IC from a remainder of the chamber, creating a sealed space between the pressure-sensing IC and the membrane filled with electrically insulating fluid, so that sensing pressure of electrically conducting fluid will not directly contact and hence not adversely affect the pressure-sensing IC by short-circuits.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an insulated IC pressure sensor, particularly to an insulated IC pressure sensor using a pressure-sensitive integrated circuit (IC) as a pressure sensor for sensing pressure of an electrically conducting fluid. 
   2. Description of Related Art 
   Conventional pressure sensors for fluids are mercury pressure sensors or mechanical pressure sensors using springs. However, mechanical pressure sensors are voluminous and expensive and have bad reactivity and reactivity. Therefore, in recent years semiconductor pressure sensors have been developed. 
   A conventional semiconductor pressure sensor uses a pressure-sensitive integrated circuit (IC), comprising, as shown on  FIG. 7 , a base  1 ; an adapter  2  on an upper side of the base  1  for connecting to a pipe and letting in fluid; an electronic circuit board  3  on the upper side of the base  1 ; a pressure-sensing IC  4 , having several feet soldered to the electronic circuit board  3 ; several wires  5 , connected to the electronic circuit board  3  for transmitting pressure data to an external processing device; and a cover  6 , placed on the upper side of the base  1  and protecting the electronic circuit board  3  and the pressure-sensing IC. 
   The pressure-sensing IC  4  has several pressure-sensitive resistors having electrical resistance values that vary with varying pressure. 
   A conventional semiconductor pressure sensor is directly contacted by fluid the pressure of which is to be sensed and hence suitable for measuring air pressure, but due to risk of short-circuits becomes ineffective if the fluid is electrically conducting. 
   Since electrically conducting fluid has to be kept insulated from the pressure-sensing IC, pressure-transmitting devices like pistons have been employed to measure pressure of electrically conducting fluid, like water or oil. As shown in  FIG. 8 , a case  7  is put over the base  1 , housing a piston  8  with an outer side, against which fluid presses causing a movement of the piston  8 . Air is used to transmit pressure from the piston  8  to the pressure-sensing IC  4 , so that pressure of the fluid is sensed indirectly. 
   Damaging of the pressure-sensing IC  4  by electrically conducting fluid is thereby avoided, but the case  7  and the piston  8  lead to dissipation of mechanical energy, lack of sensing precision and, due to usage of transmitting compressed air, temperature dependence of sensed pressure values. Furthermore, friction of the movement of the piston  8  causes the piston  8  after a release of pressure to return to a position different from an original position, resulting in poor repeatability. 
   Therefore, direct sensing of fluid pressures is not possible in many cases, limiting the range of applications, and indirect sensing is imprecise. 
   SUMMARY OF THE INVENTION 
   The main object of the present invention is to provide an insulated IC pressure sensor which allows to sense pressure of an electrically conducting fluid by direct contact. 
   For achieving this object, the insulated IC pressure sensor of the present invention has a pressure-sensing integrated circuit (IC), placed inside a chamber, and a membrane, placed inside the chamber between an inlet hole and the pressure-sensing IC, tightly sealing the pressure-sensing IC from a remainder of the chamber, creating a sealed space between the pressure-sensing IC and the membrane filled with electrically insulating fluid, so that sensing pressure of electrically conducting fluid will not directly contact and hence not adversely affect the pressure-sensing IC by short-circuits and no further mechanical pressure-transmitting device is required. 
   The present invention can be more fully understood by reference to the following description and accompanying drawings. 

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIGS. 1-4 , the insulated IC pressure sensor of the present invention comprises: a main body  10 ; an electric circuit  30 ; a pressure-sensing IC  31 ; and a membrane  20 . 
   The main body  10  has a base  11  and a cover  12 . The cover  12  is set on an inner side of the base  11 . The base  11  has a depression that forms a chamber  13 . An adapter  14  is attached to the base  11 , allowing to connect a pipe. A hole  15  in the adapter allows fluid pressure of which is to be sensed to flow into the chamber  13 . 
   The electronic circuit board  30  is placed inside the main body  10  and carries the pressure-sensing IC  31 , which is soldered thereto. The pressure-sensing IC  31  works as conventional art. The electronic circuit board  30  has a far end that extends outside of the main body  10  and has wires  32  and contact terminals  33  for transmitting pressure data to an external device. 
   Referring to  FIG. 1 , the pressure-sensing IC  31  is placed on the electronic circuit board  30  on a part thereof that lies inside the main body  10  and is aligned with the hole  15 , so that pressure of fluid that has entered the chamber  13  through the hole  15  is readily applied to the pressure-sensing IC  31 , so that the pressure-sensing IC  31  senses pressure values of fluid inside the chamber  13 . 
   The main characteristic of the present invention is the membrane  20 . The membrane  20  covers the pressure-sensing IC  31 . On an inner side of the membrane  20 , an electrically insulating fluid  23  is inserted, which transmits pressure on an outer side of the membrane  20  to the pressure-sensing IC  31 . As shown on  FIG. 3 , in a first embodiment of the present invention, the membrane  20  has a semicircular depression  21  and a peripheral flange  22 , allowing completely to cover the pressure-sensing IC  31 . The flange  22  leans against an inner side of the base  11  and is tightly connected with a surface of the electronic circuit board  30 , so that electrically insulating fluid  23  will not leak out. 
   Referring to  FIGS. 2 and 3 , for mounting the membrane  20 , the membrane  20  is, using the base  11 , pressed against the surface of the electronic circuit board  30  to be tightly connected therewith. As shown in  FIG. 2 , the surface of the electronic circuit board  30  on which the membrane  20  is laid faces the base  11 . Furthermore, as shown in  FIG. 3 , a circular groove  16  is cut into the inner side of the base  11 , accommodating the flange  22  of the membrane  20 . The cover  12  is fastened to the base  11  by screws  17 . In a fastened state, the base  11  presses against the flange  22  of the membrane  20 , which is in turn pressed against the surface of the electronic circuit board  30 , so that a tight connection is achieved. 
   Referring to  FIG. 4 , the adapter  14  on the main body  10  is connected with a pipe. The pipe allows to transmit pressure of fluid through the hole  15  in the adapter  14 . When pressure has reached the chamber  13 , nevertheless, due to the membrane  20 , there is no direct contact between fluid and the pressure-sensing IC  31  of the electronic circuit board  30 . Upon pressure, the depression  21  of the membrane  20  is deformed elastically, hence the electrically insulating fluid  23  is compressed, transmitting pressure from the membrane  20  to the pressure-sensing IC  31 , so that pressure values at the membrane  20  are sensed. Insulation by the membrane and the electrically insulating fluid  23  prevents electrically conducting fluid that has entered the chamber  13  through the hole  15  to contact the pressure-sensing IC  31  directly, so that no short-circuit will result. Therefore, sensing water and oil pressure is readily performed, without any requirement of mechanical devices for transmitting pressure, so that sensing precision is not impaired. 
   Referring to  FIG. 5 , the present invention in a second embodiment comprises: a main body  60 ; an electric circuit  30 A; a pressure-sensing IC  31 A; and a membrane  80 . The main body  60 , has a base  61  and a cover  62 , which enclose a chamber  63 . An adapter  64  is attached to the base  61 , having a central hole  65 , which allows fluid to enter the chamber  63 . The electronic circuit board  30 A is placed inside the chamber  63  and has a far end that extends outside of the main body  60 . The electronic circuit board  30 A carries the pressure-sensing IC  31  and serves as a connection to an external device. 
   The first and second embodiments of the present invention differ in mounting and fastening of structural parts thereof. The membrane  80  of the second embodiment is a circular elastic plate, mounted inside the chamber  63  between the electronic circuit board  30 A and the hole  65  and fastened by a fastening element  70 , so that no fluid entering through the hole  65  will contact the pressure-sensing IC  31 . 
   Referring to  FIGS. 5-6 , the fastening element  70  is shaped like a tube, having a first end that leans against the membrane  80 , surrounding a periphery thereof, and a second end, which is via a sealing ring  71  tightly connected with a surface of the electronic circuit board  30 A. 
   The membrane  80  and the electronic circuit board  30 A the pressure-sensing IC  31  enclose a closed space, which is filled with an electrically insulating fluid  72 . Thereby, pressure on the membrane  80  is transmitted to the pressure-sensing IC  31 . 
   While the invention has been described with reference to preferred embodiments thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention which is defined by the appended claims. 
   BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1  is a sectional view of the insulated IC pressure sensor of the present invention in the first embodiment. 
     FIG. 2  is a perspective view of the insulated IC pressure sensor of the present invention in the first embodiment when disassembled. 
     FIG. 3  is a perspective view from another direction of the insulated IC pressure sensor of the present invention in the first embodiment when disassembled. 
     FIG. 4  is a schematic illustration of using the present invention in the first embodiment. 
     FIG. 5  is a perspective view of the insulated IC pressure sensor of the present invention in the second embodiment when disassembled. 
     FIG. 6  is a sectional view of the insulated IC pressure sensor of the present invention in the second embodiment. 
     FIG. 7  (prior art) is a schematic illustration of a conventional semiconductor pressure sensor. 
     FIG. 8  (prior art) is a schematic illustration of a conventional semiconductor pressure sensor for sensing pressure of an electrically conducting fluid.