5-
9
Figure 5-10. Using Tracker 2700 to Test a Potentiometer
• The Tracker 2700 can be used to adjust a potentiometer in circuit to an approximate
operational setting. This application requires a known good board. Adjust each
potentiometer on the board under repair to match the settings on a known good operational
board. In most cases, the board under repair can now be powered up to an operational state
where it can be adjusted to true specifications.
5-2. Capacitors
With a capacitor connected to the Tracker 2700, the test signal across it responds quite differently
than a resistor. The typical tracker signature of a capacitor is an elliptical circular pattern and this
is due to the fact that relationship between the test signal current and voltage are non linear. The
current waveform is 90 degrees out of phase with respect to the voltage. The diagram below
illustrates this basic principle for capacitors.
Figure 5-12. Capacitor Circuit with Test Signal's Current and Voltage Waveforms
As the test signal's voltage crosses zero volts and becomes more positive, the current flowing in
the circuit is at its maximum and becoming smaller. By the time the voltage has reached its
maximum value, the current in the circuit has ceased flowing. As the voltage begins decreasing
toward zero, the current begins increasing toward maximum. When the voltage reaches zero, the
current is at its maximum value. Similarly, this same pattern follows as the voltage goes
negative.
Because the current is at its maximum value when the voltage is at zero, the current leads the
voltage. This is called phase shift and in a purely capacitive circuit, this phase shift equals 90°.
On the Tracker 2700, this tracker signature appears as a circular waveform. The actual shape
and slope of the elliptical signature depends on the capacitance and impedance value of the
component and the test signal's internal resistance and frequency
.
Capacitor Tracker Signatures
The goal of this part is to explore some capacitive signatures and to help you understand how
capacitor signatures are related to:
• The capacitance (µf) of the circuit under test
• The frequency (F
s
) of the test signal
• The voltage (V
s
) of the test signal
• The internal resistance (R
s
) of the Tracker 2700
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