Secondary Delay

[1843]

Hi all,
Some PI machines can ignor the small objects;
Does it depend on secondary delay?
What does secondary delay do?

Regards

[bbsailor]

1843
Some PI machines can ignor the small objects;
Does it depend on secondary delay?

It more depends on the main delay and the size of the coil to ignore small surface targets and detect larger deeper targets. Although, the second delay adjustment could help reduce the signal from targets with a longer decay signal.

What does secondary delay do?

Secondary sample reduces low frequency noise. It works like this. The second delay is adjusted so that most of the signal from the desired target has decayed to zero, then the second delay sample window is opened. This second delay signal is then subtracted from the main signal. If all or most of the target signal is in the first delay signal, then the target signal will not be affected. If you set the second delay too short, you will begin to reduce the strength of the target signal. Noise in both the first and second delay sample is the same so the noise will be mostly cancelled. Adjust the second delay so the strength of the desired target is not reduced.

Some PI detectors label the second delay control, "NOISE".

bbsailor

[1843]

bb

Many thanks for your guidance!
All the best

[Reg]

Hi 1843,

One of the other uses for the secondary sampling is to eliminate signals from certain hot rocks. Rocks such as magnetite can sound off if the pulse is strong enough and there is no secondary subtract signal.

Also, without the secondary sampling, you can also get a signal simply from the motion of the coil because the coil will pick up the earth's magnetic field if the gain is high enough. The later sample (the secondary sample) will also detect the signal and will be used to subtract it, so it isn't heard.

Reg

[1843]

Hi Reg

Thank you!
Your information is very useful.