Top Tip for Eddy Current NDT Users No 3

How to get the most out of your equipment.

In order to get the best signal to noise (electronic) out of your Eddy Current NDT equipment. You need to set the input amplifier gain as high as possible without saturating the front end of the instrument. The Vantage pre-ampifier gain can be set in 0.1dB increments(ensuring optimal setting of tis paramter). Some equipment (like ETher NDE’s Vantage) have indicators to show you this situation. If not then it is important that you verify you get spot movement after this adjustment. You may get no movement at all (showing both the x and y axis detector are saturated) or a very straight line (indicating one axis of the detector is not saturated).

Increasing the drive voltage level can have a similar affect, however there are two problems here:-

a) You can potentially destroy the probe (probably unlikely below 5v pk-pk drive) particularly if you are using a probe well below the manufacturers stated centre frequency.

b) if the sine wave drive signal is noisy (eg due to steps in digitisation) then the noise level will be unchanged beyond a certain level.

Why is this so?

The noise of the front end amplifier (input amplifier or pre-amplifier) is constant. So if gain is applied after the front end the noise is amplified. So it is best to have the input amplifier gain as high as possible so that the subsequent gain is as low as possible.

n order to get the best signal to noise (electronic) out of your Eddy Current NDT equipment. You need to set the input amplifier gain as high as possible without saturating the front end of the instrument. Some equipment (like ETher NDE’s Vantage) have indicators to show you this situation. If not then it is important that you verify you get spot movement after this adjustment. You may get no movement at all (showing both the x and y axis detector are saturated) or a very straight line (indicating one axis of the detector is not saturated).

Increasing the drive voltage level can have a similar affect, however there are two problems here:-

a) You can potentially destroy the probe (probably unlikely below 5v pk-pk drive) particularly if you are using a probe well below the manufacturers stated centre frequency.

b) if the sine wave drive signal is noisy (eg due to steps in digitisation) then the noise level will be unchanged beyond a certain level.

Next

Next month influence of filters on signal to noise 

 

All the best

 

John Hansen

ETher NDE

www.ethernde.com

 

 

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