The hammer switch (trigger switch) that Geometrics seismographs use is a contact closure device that utilizes inertia force to create a momentary closure between the center rod and cylinder located in the enclosed device.

The delay from strike to closure can vary based on orientation. The black dot on the switch and instructions were added to assist having a repeatable strike to closure time from usage to usage. However, this is only true for one hammer switch. From one hammer switch to the next there could be a variance however very slight indeed. In SCS there is a setting which lets the user change the sensitivity of the hammer switch to accommodate the natural variance in the trigger switches.

To build the switch, we use a tool to center the spring beam in the tube contact, which minimizes the variance in the triggering of the hammer switch between different orientations and natural variations in different hammer switches. Any strike to closure time variance is more affected by the energy of the strike and the momentum produced on the hammer switch.

The usage of the black dot to orient the hammer switch for most cases is probably extraneous. We center the beam accurately and suggest the usage of the black spot for mounting repeatability. We left it just to ensure any slight difference due to orientation could be eliminated. Additionally, both the tube and spring beam are gold plated to reduce and maintain contact resistance. After all this, it depends upon the repeatability of the user’s apparatus.