Abstract: A subsurface geophysical parameter measurement is converted downhole to a first pulse train whose instantaneous frequency is a function of the parameter value. In response to a first control signal, a first counter begins a first count of pulses from the first pulse train, and a second counter begins a count of second pulses from a downhole reference oscillator. The first and second counts are terminated in response to a second control signal and the first and second counters are interrogated. A ratio is then developed between the first and second counts which is functionally related to the value of the parameter.

Abstract: A telemetering system provides improved cable utilization and bi-directional digital communication between a logging sonde and surface electronics over a single balanced transmission line of a multi-conductor logging cable, with significant signal crosstalk reductions. Receiver circuitry downhole decodes pulses delivered on the line from a surface logic generator which fire transmitter-receiver pairs of an acoustic logging tool in an order defined by the pulses. A PCM transmitter in the sonde thereafter samples data generated by other logging instruments, encodes this information into digital data frames, and transmits the data on the same line to a surface PCM receiver. Circuitry limits surface and downhole receiver response to PCM transmitter and logic generator pulses, respectively. A center tap of the same transmission line also provides for simultaneous noise-free transmission of sensitive low level signals such as remote surface potential and the like to the sonde.