Sensitivity vs. Ground Balance

[landman]

I understand the sensitivity control regulates something within the circuitry that enables the detector to become more or less sensitive
which means less or more depth. Sensitivity can be cranked up when the electrical interference and ground mineralization is both low.

Now ground balance is set so as to have a mineralization zero point or reference point so as to neutralize the soil so that it does not appear as a target.

I understand that after manually ground balancing a detector and that detector is experiencing falsing that one can reduce the sensitivity
re grond balance and that may do the trick.

My questions are this:
What does sensitivity knob actually do electronically?
What does the Ground Balance actually do electronically?
What is the difference between these 2?
How do they inter-relate?

Thanks guys and gals.

 

[Reg]

Your questions are good ones. So, for a PI, the following occurs. VLF's often are somewhat similar.

Now, the sensitivity knob simply increases the gain of an amplifier. The gain is the ratio of the feedback resistor over the input resistor. So it is RF/RI Now if you increase the RF then you increase the sensitivity. In the case of most sensitivity controls such as those on Eric Foster's PI detectors, there is an amplifier, usually the last or near the last opamp that has a potentiometer as RF. So, when you increase the sensitivity you increase the resistance of the pot.

Ground balance is totally different in the fact that main samples are taken and amplified and a set of later samples are also taken and ultimately subtracted from the main samples. When the gain of the later sample equals that of the main sample, whatever signal that has that gain will cancel, thus no response. So, in a nutshell, this works on a subtraction process.

Now, the GB control adjusts the gain of the GB amplifier. Once the ground signal in the GB amplifier equals that of the ground signal in the main channel, then the two cancel each other out. There is no direct relationship to the sensitivity control.

Above is a very simplified version of what happens. The actual action of a PI is much more complex and can't be explained in a few paragraphs.

Reg

 

[landman]

Now, the sensitivity knob simply increases the gain of an amplifier.

Reg

So Reg are you saying that the sensitivity know adjusts the output of the RX?

 

[Reg]

The sensitive knob usually does not adjust the output of the RX coil directly. Instead, the RX coil signal is amplified, demodulated, autotuned, and then amplified before it reaches the stage where the sensitivity control is located.

Now, if you are thinking VLF, then things get even more complicated since, on the cheaper VLF's, the sensitivity control only adjusts the discrimination circuitry. On other VLF's, the RX signal is amplified and then the sensitivity control adjusts the gain going to additional amplifiers.

Reg