while the specification concludes with claims defining the features of the invention that are regarded as novel , it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures , in which like reference numerals are carried forward . referring now to fig6 there is shown an electrical contact assembly 600 in accordance with the invention . assembly 600 includes first and second housing members 602 and 604 that retain five guide wire spring contacts 606 - 614 . assembly 600 takes the place of housing members 514 and 530 and contacts 542 , 544 and 546 in fig5 . in fig7 there is shown a pressure guide wire 700 in accordance with the invention . similar to guide wire 10 , pressure guide wire 700 includes three conductive sleeves or contacts 702 , 704 and 706 . however , unlike guide wire 10 , the two outer contacts 702 and 706 are wider than the middle contact 704 . the wider sleeve contact 702 and 706 are designed so that they can make contact with two corresponding contacts each from among contacts 606 - 614 . guide wire sleeve contact 702 is designed to make an electrical connection with contacts 606 and 608 and sleeve contact 706 makes electrical connection with contacts 612 and 614 when guide wire 700 is placed in assembly 600 . the center guide wire sleeve contact 704 makes electrical connection with center contact 610 . housing assembly 600 has been designed to be backward compatible and will accept either the newly designed guide wire 700 or the prior art guide wire 10 . when guide wire 10 is inserted into assembly 600 , sleeve contact 306 makes connection with contact 612 , sleeve contact 304 makes connection with contact 610 and sleeve contact 302 makes connection with contact 608 . in fig9 there is shown a simplified electrical representation of the preferred embodiment precision interconnect circuit which solves for the variable contact resistance &# 39 ; s and provides for backward compatibility with both the old pressure guide wire 10 and the new pressure wire 700 . the pressure sensor 208 is coupled to sleeve contacts 702 , 702 ′, 704 , 706 and 706 ′ when a new pressure guide wire 700 is being used . when an old pressure guide wire 10 is being used , contacts 702 ′ and 706 ′ are not utilized since the outer sleeve contacts are not as wide as those shown in pressure wire 700 . in fig9 contacts 702 ′ and 706 ′ are simply representing the extra wide sleeve contacts found in contacts 702 and 706 as shown in fig7 . the variable contact resistance problem of the interconnection is highlighted within box 920 . sleeve contacts 702 ′, 702 , 704 , 706 and 706 ′ are coupled to corresponding contacts 614 , 612 , 610 , 608 and 606 in the new design which form the input port for the interconnection circuit . when an old pressure guide wire 10 is attached , contacts 614 and 606 are not utilized . switches 910 and 912 remain in the open position or first state when a new guide wire 700 is attached and are automatically placed in the closed position or second state when an old guide wire 10 is attached in response to a control signal . the control electronics for switches 910 and 912 will be discussed in detail further below . switches 910 and 912 allow for the interconnect interface to be backward compatible and support both pressure guide wire 10 and the new pressure guide wire 700 . in the interconnection interface , new pressure guide wire 700 uses a 5 - wire interconnection , while the old pressure guide wire uses a 3 - wire interconnection . a pair of differential operational amplifiers or precision amplifiers 902 and 904 that have high impedance inputs and are part of the interface circuit allow for three low current paths . these paths take away the effect of changes in the contact resistance ( 924 , 926 and 928 ) from changes in the sensor resistors 402 and 404 . a reference current is provided to the sensor resistor 402 and 404 as shown in order to generate the appropriate voltage drops used for pressure change detection . referring now to fig1 and 11 , there is shown a full electrical schematic for the interface circuit which replaces the electronics found in interface box 24 . the circuitry shown in fig1 and 11 includes not only the circuitry needed to perform the precision interconnection as described above , but also provides the necessary signal conditioning circuitry needed to match the signal from the pressure sensor 208 to the pressure measurement console 28 . the signal conditioning circuitry will not be discussed in detail since it is not needed in the understanding of the present invention . the circuit shown in fig1 is the mother board and the circuit shown in fig1 is a daughter board which in the preferred embodiment comprise two separate printed circuit boards which are coupled together . the two circuit boards are coupled together using jack connectors j 1 and j 2 found in the circuit of fig1 which mate with corresponding plug connectors p 1 and p 2 located on the circuit of fig1 . connector “ jp2 ” 1002 in fig1 is coupled to the pressure sensor resistors 402 and 404 which are coupled through via connectors 32 and 34 into the interface circuitry . the five sensor contacts are coupled to pins 2 , 4 , 6 , 8 and 10 of connector jp2 as shown in diagram 1014 . differential amplifiers 902 and 904 as previously shown in fig9 that are part of amplifier stage 1008 , provide a gain of approximately two . the output of these amplifiers are fed into a 2 pole , 250 hertz low pass filter ( lpf ) stage 1012 which provides for a gain of approximately twenty . the outputs of the lpf stage 1012 are coupled to connector “ jp1 ” 1010 that in turn couples into the pressure monitoring console 28 . pins 7 and 9 of connector jp1 are inputs to the pressure monitoring console , while pins 1 , 2 , 4 , 6 , 8 , 10 , 14 , 15 and 16 are signals coming from the pressure console 28 into the interface circuitry . although not important to the understanding of the present invention , circuit block 1004 , provides offset voltage correction for the interface between the pressure guide wire 700 and the pressure monitoring console 24 . box 1016 shows the internal interconnections of connector j 2 . in fig1 , operational amplifiers u 5 a , u 1 a and u 1 b form a buffer stage 1108 that provides signal buffering . block 1104 forms an oscillator circuit that provides a signal of about 10 - 12 kilohertz . this signal is used to determine whether an old pressure guide wire 10 or a new pressure guide wire 700 is coupled to the interface circuitry in accordance with the present invention . a synchronous demodulator circuit 1102 takes the oscillating signals and provides a control signal 1106 that is used to control switches 910 and 912 . switches 910 and 912 remain open when pressure sensor 700 is attached and are closed when pressure wire 10 is attached . the output of demodulator circuit 1102 passes through a two pole 30 hertz low pass filter stage 1112 having a gain of approximately thirty . fig1 shows a simplified block diagram of the electrical schematics of fig1 and 12 as interface circuit 1200 . pressure wire 700 is coupled to connector 1002 that is in turn coupled to the interface switch circuit 1110 comprising the two digital switches 910 and 912 . the output of the digital switches is passed through a buffer stage 1108 prior to being sent to the differential amplifier stage 1008 comprising differential amplifiers 902 and 904 . the output of the differential amplifier stage 1008 is sent to the 2 pole 250 hertz low pass filter stage 1012 before the signals are sent to console 28 . a reference voltage generator stage 1202 provides the necessary voltages to the circuit . as previously mentioned in order to provide for backward compatibility between the old pressure wire 10 and the new pressure wires 700 , an oscillator 1104 and demodulator 1102 are used to provide a control signal 1106 which either closes switches 910 and 912 or leaves them in the open position . when a new pressure wire 700 is detected , the control signal 1106 leaves the switches 910 and 912 in the open state , while if the old pressure wire 10 is detected control signal 1106 causes the switches to go to the closed state . by using a high frequency ( 10 - 12 kilohertz ) signal having low amplitude to make the switching determination between the 3 - wire and 5 - wire guide wires , prevents any stray noise and interference from affecting the control signal . also , the use of such a low amplitude - oscillating signal prevents the signal from affecting the measurement of pressure sensor resistors 402 and 404 . a large signal at capacitor c 2 causes control signal 1106 at the output of inverter 114 to be logic high closing the switches 910 and 912 indicating a 3 - wire pressure wire 10 is connected to the interface circuit . while a low signal at capacitor c 2 caused by the connection of a 5 - wire pressure wire 700 causes the control signal 1106 to be at a low logic level leaving switches 910 and 912 in the open position . the present invention with its use of high input impedance differential amplifiers 902 and 904 to measure pressure sensor resistors 402 and 404 avoids the problem caused by changing contact resistance 922 - 930 . also , the automatic switching technique disclosed above provides for a system which is backward compatible between pressure guide wires 10 and 700 . while the preferred embodiments of the invention have been illustrated and described , it will be clear that the invention is not so limited . numerous modifications , changes , variations , substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims . for example , although the preferred embodiment has discussed forming a precision interconnect for a rotating connection , the present invention is not so limited and can be used for non - rotating connections . the present invention can be used for not only with a pressure guide wire it can be used with other devices that need proper measurement of electrical parameters from the device . also , instead of monitoring a pressure sensor 208 utilizing two resistors 402 and 404 , the present invention can be used to provide a precision interconnect for devices having any number of resistors . if the number of resistors that need to be monitored change , a change has also to be made as to the number of monitoring devices such as differential op - amps 902 and 904 need to be used .
an electrical device such as a pressure guide wire which has a resistive pressure sensor , such as a piezoresistive sensor , uses a precision interconnect in order to provide proper pressure measurement readings . the precision interconnect helps avoid the effects of contact and line resistance on the measurement of the pressure sensor &# 39 ; s resistors . the precision interconnect uses high input impedance device &# 39 ; s such as differential operational amplifiers in order to overcome the effect of any changes in the contact resistance . further , an interface switch which is responsive to a control signal automatically determines what type of pressure guide wire is attached to the interface circuit .