off the generation of the tension pulses before firing the perforating gun 38 more particularly fig3 depicts an upper portion 20 a of the tool 20 and fig4 and 5 depict a bottom portion 20 b of the tool 20 for different states of the tool 20 as described below as shown the tool 20 includes a housing 50 that encases the components of the tool 20 such as a weight 70 see fig4 and 5 that resides in an interior chamber 51 of the housing 50 in a first state depicted in fig5 of the tool 20 the weight 70 is held as described below in suspension over a contact surface 90 of the housing 50 by a latch or brake formed by a split collar 61 and a release shaft 74 that are described below when a magnetic casing collar sensor 98 see fig3 of the tool 20 detects a casing collar circuitry of the tool 20 causes the brake to release the weight 70 an action that causes the weight 70 to travel a distance d see fig5 and strike the surface 90 see fig4 to generate the tension pulse 24 in some embodiments the brake is designed to selectively grip a threaded shaft 64 see fig4 and 5 that is coupled to the weight 70 to control the rise and fall of the weight 70 in this manner the brake releases the shaft 64 to allow the weight 70 to fall and strike the surface 90 and the brake grips the shaft 64 so that the weight 70 may be retracted as described.