Design and fabrication of a thin-film ratiometer for electronic timer of XM732 proximity fuze

A feasibility study was conducted on the design and fabrication of a thin-film precision ratiometer developed for use in the electronic timer of the XM732 Short Intrusion Proximity Fuse. The ratiometer network consists of a 432-kohm linear variable resistor and a 3-kohm fixed resistor that provides a means of setting a delay time of 2 to 144 sec before fuse turnon. Nichrome and gold were vacuum deposited onto a glazed ceramic substrate with the resistor-conductor pattern being selectively etched. This approach utilizes a step-like conductor/commutator design that permits settability within 0.5 sec through a movable spring contact. Resistor tolerances of plus or minus 20 percent with a linearity of plus or minus 1.5 ratio units through an angle of 324 deg were demonstrated.