An electro-mechanical wireline assembly as shown for anchoring a wireline tool string in place during a wellbore under balanced well conditions. The frequency altering device receiving the first beam of light and transmitting a second beam of light having a second frequency. The second component is injected through a second orifice of the nozzle means. As a result of that cross correlation, an output record, known as a correlation spectral volume, is generated. If the first or second sensor fails, a differential signal is generated between the output signal of the remaining functional sensor and the third sensor.