The Stat Eliminator circuit has been around for decades. The original Stat Eliminator was a vacuum tube (valve) based affair, but Al Biggs (of SIE fame) perfected the solid state circuit shown above in the 1970's. This ingenious circuit uses a feedback arrangement to cancel hash type noise without suppressing "real information". The Stat Eliminator proved useful in the early days of computer based logging when analog surface module output was sometimes too noisy to feed directly into digitizing electronics. See our complete schematic of the SIE Stat Eliminator (pdf file).| Home | Tech & Tips | Surface Hardware | Cement Bond Log | Nuclear Log |
The Stat Eliminator was primarily developed to address the statistical fluctuation problem inherent with radiation measurements. As an example, in Gamma Ray tools, the intensity with which radiation affects the detector at a given depth is not constant, but rather varies due to the unpredictable and random number of atomic disintegrations during a given time interval (see The Gamma Ray Log). Thus the Gamma Ray tool will produce a variable reading even when the tool is held stationary, as seen on the "statistical check" often appended to a Gamma Ray Log. A "time constant" circuit is used to average the counts over a period of time, giving a more usable and repeatable log. But long time constants tend to excessively "smooth" the log, and also require slower logging speeds (see Logging Rules of Thumb for time constant formulae). The Stat Eliminator can be fitted to a ratemeter, allowing a faster time constant than would otherwise be practical. The Stat Eliminator essentially filters out the statistical noise, but preserves meaningful changes in count rate. Many SIE ratemeters were factory equipped with the Stat Eliminator circuit, and we have installed said circuit in scores of other ratemeters, including the GO / GOI / MLS RMM 210.
Another popular application of the Stat Eliminator has been in SIE style cement bond logging panels. With the addition of a Stat Eliminator to the amplitude output, the value of the integration capacitor can be halved, resulting in greatly enhanced detail in the amplitude curve (the collar signature in free pipe is greatly improved). However, the Stat Eliminator is not the optimal solution in this case, and cannot be used to ameliorate the travel time curve. AnaLog Services, Inc. has a proprietary active filter that produces improved amplitude and/or travel time curves without the overshoot seen with the Stat Eliminator in this particular application. See our Cement Bond Log Related Printed Circuit Boards (PCBs) page for both the Stat Eliminator and the active filter discussed above.
Paul Knight, our good friend and logging repair guru, has described the Stat Eliminator as magical, and that it is. Said circuit remains a useful tool decades after its development.