Abstract: A pet door kit made of frame sides and door sides all of which may be assembled onto a mesh screen panel before the panel is required to be cut to allow for pivoting of the door. Advantageously each frame side is formed as an integral molding with an associated door side so that the skill of the installer is not required to locate the door within the frame. Economically, the two moldings thus provided are identical and securing members, i.e. pins are integrally provided to pass from one molding, through the mesh, and be force fitted into holes in the other molding. The assembly of the two moldings simultaneously and quickly assembles the door and frame onto the firm unsevered rigid support of the screen panel.

Abstract: Amplification or generation of very low (and variable) frequency, low voltage, high current bipolar signals useful in electrical borehole telemetry systems is achieved using a duty cycle control device for causing the alternate direct application of a positive voltage and a negative voltage to an integrator. A commutated clamp is connected to the input of the integrator for switchably connecting the integrator directly into a current loop with the load, connected to the output of the integrator, when neither voltage is being applied to the input of the integrator.

Abstract: Amplification or generation of very low (and variable) frequency, low voltage, high current bipolar signals useful in electrical borehole telemetry systems is achieved using a duty cycle control device for causing the alternate direct application of a positive voltage and a negative voltage to an integrator. A commutated clamp is connected to the input of the integrator for switchably connecting the integrator directly into a current loop with the load, connected to the output of the integrator, when neither voltage is being applied to the input of the integrator.