TTI i-Prober 520 Manual De Instrucciones página 10

Calibration for Quantitative Measurements on PCB tracks
The relationship between the output voltage seen on the scope and the actual current in the PCB track
depends on a complex relationship between the width of the track, the width of the sensor inside the
current probe, and the thickness of the probe insulation between the track and that sensor. To obtain
quantitative measurements the sensitivity adjustment on the control box must set to suit the particular
track width being measured. The wider the track, the lower the field strength for a given current, so the
greater the gain required to obtain a sensitivity of 1A/V. At track widths above about 3.5mm the control
box gain cannot be increased sufficiently to give a sensitivity of 1A/V so the system must be adjusted for
a sensitivity of 2A/V.
This relationship between track width and the gain required is incorporated into the calibration graph
below. The calibration procedure involves placing the probe into the calibration hole in the control box
and applying the calibration current. The sensitivity control is then adjusted to obtain the particular output
voltage (as measured by the scope trace) to suit the intended track width. The calibrator can produce
either a square wave or DC calibration current. To avoid difficulties caused by the influence of the earth's
magnetic field and the local magnetic environment, calibration is normally performed using the square
wave signal, obtained by setting the switch to the AC ( ) position. The signal is a square wave at about
1kHz. The amplitude setting refers to the peak-to-peak voltage between the flat parts of the square wave,
ignoring any overshoot on the transitions.
Detailed Procedure
First, decide on the width of the track for which a calibrated measurement is required. Then, using the
graph, look up the peak-to-peak output voltage setting for that track width and set the scope to a suitable
sensitivity (for example, 1 Volt per division for narrow tracks, or 0.5 Volt per division for wider tracks).
4
3.5
3
2.5
2
1.5
1
0.5
0
0
10
I-prober 520 PCB sensitivity setting
For 1 Amp/Volt
1 2
For 2 Amp/Volt
3 4
Track Width (mm)
5
6
7