Tracker-2800-2800S.pdf - 第18页

18 Range Volts/Div 20V 5.00 15 V 3.75 10 V 2.50 5 V 1.25 3 V 0.75 200 mV 0.05 Table 2-3 Tracker 2800 Horiz ontal Sensiti vities The Signature viewing ar ea of the LCD screen can also be set up in quadrant s to show posit…

Figure 2-7: Tracker 2800 Core Circuit Block Diagram

= Source Resistance, V

= Source Voltage, R

= Load Resistance, F

= Source Frequency

Each test signal or range has three parameters: source voltage V

, resistance R

and source frequency

. When using ASA for troubleshooting, the objective is to select the range that will display the most

descriptive Tracker signature information. The Tracker 2800 can readily accomplish this by changing

the proper range parameter. The source voltage V

of the test signal can be used to enhance or

disregard semiconductor switching and avalanche characteristics. The F

or frequency of the test signal

source can be used to enhance or disregard the reactive factor (capacitance or inductance) of a

component or circuit node.

Horizontal Axis

The voltage across the component under test controls the amount of horizontal trace deflection on the

LCD display. When the component under test is removed, creating an open circuit (e.g., R

= ), the

voltage at the output terminals is at its maximum and thus the trace on the display is a straight

horizontal line with its maximum width.

The horizontal axis is divided up by small graticule lines similar to those on a conventional

oscilloscope CRT. Each mark is approximately 1/4 of the peak range voltage. For example, in the 10 V

range, each division is approximately 2.5 V. You can use these graticule marks to get a rough estimate

of the voltage drop across the component under test. Changing the V

of the test range effectively acts

the same as changing the Volts-per-division on an oscilloscope. Table 2-3 shows the volts per division

for each Tracker voltage range.

Range Volts/Div

20V 5.00

15 V 3.75

10 V 2.50

5 V 1.25

3 V 0.75

200 mV 0.05

Table 2-3 Tracker 2800 Horizontal Sensitivities

The Signature viewing area of the LCD screen can also be set up in quadrants to show positive and

negative current and voltage characteristics. Refer to figure 2-8.

Figure 2-8. LCD Display Horizontal Axis and Graticule Lines.

When the test signal is positive, this means that the voltage and current are positive so the signature's

trace is on the right hand side of the LCD display. When the test signal is negative, the voltage and

current are negative so the trace is in the left hand side of the display.

Turn on the Tracker 2800 and observe the LCD display. With nothing connected to its test terminals,

the display trace is a horizontal line (R

=) as shown in figure 2-9.

Figure 2-9 Tracker 2800 LCD Display with Open Test Terminals.

Vertical Axis

The amount of vertical trace deflection on the LCD display is controlled by the voltage dropped across

the internal impedance R

of the Tracker. Because R

is in series with the load R

, this voltage will be

proportional to the current flowing through R

. This current that flows through the component under

test is the vertical part of the signature.

When the R

is zero ohms (0) by shorting the output terminal to the common terminal, there is no

voltage dropped across R

causing no horizontal component displayed in the Tracker signature. This

short circuit signature is a vertical line trace on the LCD display.

Connect the red microprobe to the output channel A jack on the Tracker 2800 and the black

microprobe to the Common jack. Touch and hold the probes together and observe the Tracker

signature on the LCD display.

You will see a vertical line trace in the middle of the LCD display.

Figure 2-10. LCD Display with Vertical Axis, Graticule Lines displaying a short circuit.