The SARK-110 lower frequency range is limited by the hardware and the software of the device to 100 kHz. This limit is not an issue for most use cases, but for some applications such as eddy current measurements it is required operation at even lower frequencies.After installing the new firmware it is necessary performing the detector calibration first and then the OSL calibration.
Note: these Hardware Modifications described below are already implemented in units sold starting September 2014
However, it is possible to overcome this limitation and prepare the unit for a low frequency range limit of 5 kHz by replacing six capacitors and downloading a variant of the firmware.
Note that it is convenient purchasing additional spares because they are very easy to lose during the assembly (at least it happened to me).
The location of the capacitors in the board is illustrated in the Figure 1.
Figure 1, Changed capacitors
The download location is at the bottom of this page and for upgrading you will need to follow the instructions described in the User’s Manual.
Following reference is an excelent source of information about eddy current testing: An introduction to eddy current testing from the NDE/NDT resource center
For this example, I built the probe coil shown in Figure 2. This is build of 0.35mm copper, and four layers of about 25 windings per layer. The radius of the coil is 7.4mm and height 9.6mm.
As measurement targets I used a FR4 board (Figure 3) and aluminium board (Figure 4).
Figure 2, Coil
Figure 3, FR4 Board
Before performing the measurements it is necessary doing OSL calibration. For the measurements, select Scalar Chart mode and <Ls> for the left axis and <Zs> for the right axis. Then select the desired frequency range.
Following screenshots show the measurements in free space (Figure 5), FR4 board (Figure 6) and aluminium plate (Figure 7). You will easily observe the variations in the inductance of the probe coil due to the different conductivity of the measurement targets.
Figure 5, Measurements in free space
Figure 6, Measurements with FR4 board
Figure 7, Measurements with aluminium plate
Application Notes >
Extending low frequency range limit down to 10 kHz
|Selection||File type icon||File name||Description||Size||Revision||Time||User|
|SARK-110 Firmware v0.9.3; Freq range:10kHz - 230MHz||116k||v. 1||Mar 3, 2017, 7:51 AM||Melchor Varela|