Current switching technique

A redundancy circuit comprising, in combination:

• a measuring impedance;
• a plurality of operational amplifiers having inverting input terminals, non-inverting input terminals, and output terminals;
• a source of excitation voltage with respect to ground;
• means connecting said source through said measuring impedance producing a signal current into said inverting input terminals;
• means grounding said non-inverting input terminals;
• a like plurality of further impedances having first terminals connected respectively to said inverting terminals of said amplifiers;
• and switch means having a plurality of conditions in each of which a selected one of said further impedances is connected between the output terminal and the inverting input terminal of a selected one of said amplifiers, and the remaining further impedances are connected between the inverting input terminals of the remaining amplifiers and ground.

In a redundancy circuit, in combination;

• an input bus;
• means continuously supplying said bus with a signal current through a measuring impedance;
• a plurality of operational amplifiers having output terminals and inverting and non-inverting input terminals;
• means continuously connecting the inverting terminals of said amplifiers to said bus and grounding the non-inverting input terminals;
• a like plurality of switch means each having a movable contact and a like plurality of fixed contacts engagable thereby in a predetermined sequence;
• a plurality of feedback impedances;
• means continuously connecting each of said feedback impedances between said bus and one of said movable contacts;
• means severally connecting said output terminals to different ones of the fixed contacts of said switch means in the same succession;
• and
• means grounding the remaining fixed contacts of all said switch means.