Что такое asa using a curve tracer

Analog Signature Analysis Using a Curve Tracer · Analog Signature Analysis Using a Curve Tracer Page 3 of 5 Leakage current is indicated by curvature of the linear portions and the

Analog Signature Analysis Using a Curve Tracer Analog Signature Analysis (“ASA”) is a “power off” troubleshooting technique that applies a sine wave (AC) stimulus to a component creating a voltage vs. current signature. A curve tracer, or ‘Octopus’ is an inexpensive piece of testing equipment that utilizes ASA and uses an oscilloscope as a display but allows you to test components with the power turned off. The curve tracer (Fig. 1) can be used with any type of oscilloscope and consists of a 6.3-VCT filament transformer, three ½-watt resistors, and two test probes. Half the filament voltage is applied to a voltage divider consisting of R1 and R2 yielding 1-volt ac at the top of R3. This voltage can be applied to any component or combination of components across which the test leads are placed. The current is limited to 1 mA by R3. The voltage across the probes is applied to the horizontal input of a scope, while the voltage across R3 as a result of the current through it is applied to the vertical input. What we see on the scope is actually a display of the voltage across a component under test versus the current through that component.

Figure 1 Schematic of the Curve Tracer Testing Device

R1 To Vertical +—/\/\—-+——-+——-> Scope Output | 220 | | («Y») 6.3V | Ohm | \ XMFR | | R3/1K >o—)||( | | \Ohm )||( CT | | | 117VAC )||(—-+ \ +—+—> To Scope GND )||( R2/100 | >o—)||( \Ohm | | / +===> Black Probe | | | | To Horizontal +—————-+———-+—-> Scope Output | («X») | +====> Red Probe

Analog Signature Analysis Using a Curve Tracer

You must have a dual channel oscilloscope capable of operating in the «XY mode» in order to use a curve tracer. In the XY mode, one channel is switched from a vertical input (Y) to a horizontal input (X) replacing the normal horizontal timebase generator. To use the curve tracer, set your oscilloscope to the XY mode and adjust the X and Y position controls so the spot is in the dead center of the oscilloscope’s CRT display. Connect the curve tracer to the oscilloscope and plug in the transformer. With the two leads open (not touching each other or anything else) adjust the X input for as large a trace as you can without going off the sides of the CRT. Under these open-circuit conditions the full 1-volt ac appears across the horizontal input. Since no current is being drawn through R3, no voltage appears across it or the vertical input. Short the two leads together and adjust the Y input the same way. With the test leads shorted together, the trace flips to a vertical line. The vertical amplifier gain is adjusted to give a 2” trace. The shorted test leads short out the horizontal input and cause the full 1-volt of ac to appear across R3 and so across the vertical input. All ASA signatures are made up of four basic components: resistance (any value from an open to a short), capacitance, inductance, and semiconductance. Resistors have a constant voltage/current ratio causing a linear diagonal signature with the angle of slope being directly proportional to the resistance value. Capacitors and inductors cause a phase shift between voltage and current producing a circle or elliptical signature directly proportional to the amount of capacitance or inductance. Diodes, the simplest semiconductive device, allow current to flow in one direction and not the other. These signatures are displayed by a horizontal line that goes vertical just after the center axis of the display. It is with semiconductors that the curve tracer really excels. Normally, you would use a meter set to the “diode test” to test diodes, transistors, voltage regulators and integrated circuits. The meter will unambiguously test the vast majority of semiconductors but every now and then a transistor will test “good” with a meter, but breakdown when it is operating at full voltage and current. The curve tracer is better at identifying this type of unusual problem. The curve tracer can also be used to test all types of integrated circuits. Complex or composite signatures are combinations of the four basic ASA signatures. Integrated circuits are made up of transistors (which are a combination of diodes), resistors, and capacitors. The signatures displayed by ICs are composites signatures. These devices have built-in protection circuits, which allow current to flow in both directions displaying a signature that is vertical in the bottom half, then horizontal, then vertical in the top half. These signatures are typically called “chair patterns”. Common zener diodes will display a chair pattern that has a vertical break-over point at 0.6 volts (the conducting voltage of a silicon device) and a second break-over point at the rated voltage for the zener diode. Variations of this signature found in ICs are due to resistive and capacitive elements. CMOS integrated circuits are built with capacitors causing their signatures to display a loop in the “back” of the chair pattern.

V-I Tester (aka ASA or Octopus or curve tracer)

I want to build a simple V-I tester and based on this article (or this) I did this easy circuit:

R1 = 560Ω
R2 = 100Ω
R3 = 1kΩ

where R1 and R2 is a voltage divider to set the \$V_<(DUT+V_)>=1VAC\$ and R3 limit the current in the Device Under Test.

I used this transformer, with 6.3V, 10 VA output (is dual, but I use only one output).

1. If I change the voltage divider resistors to \$R_1=56Ω\$ and \$R_2= 10Ω\$ (especially), isn’t better? With 10Ω I will reduce the output impedance of the circuit that feed the DUT, thus I don’t load the source because it is in parallel to the \$R_3+R_\ge1000Ω\$ and then \$R_3+R_\gg R_1\$ , isn’t?
   BTW the current I draw is \$I =\frac<6.3><66>\approx 100mA\$ and the output power is at the "safe" value of: \$6.3V\cdot100mA = 0.63VA\$
2. With this voltage divider I have a voltage less than 1VAC across the DUT. The article says that I can test also Diode, Zener, etc. How is possible with this small voltage?

1 Answer 1

Here is what you can do, with a little effort .
This is for BJT-type NPN. Here, R4 is stepped 100 k -> 1000 k.
See the "visual" change of "beta" .

@Circuit fantasist . and all those interested 🙂 .
Here is a simulation to explain the choice of "voltage" and "resistor" to see the full curve of a DUT with "negative" resistance (NB: Voltage vs current, as with UJT device) .
NB: the part of the "unstable zone" can’t be seen if the 2 conditions (voltage, resistance) of "loading" are not met.

Сurve tracer Assist-ASA

Curve tracer of voltmeter and impedance signatures Assist-ASA is a hardware-software complex designed for technical diagnosis and troubleshooting in electronic digital, digital-to-analogue and analogue circuits, modules and units using parametric method.

Assist-ASA has the possibility of troubleshooting (of microchips, transistors, capacitors, resistors etc.) on the board of unit under testing (here and after – UUT) without supplying it with feeding voltage.

Curve tracer can be used by staff without high qualification. It also provide conditions to make a repair of electronic modules quickly even if basic circuit diagrams are absent or not found.

Troubleshooting of UUT is performed with parametric method VI (UI, ASA) by measuring volt-ampere signatures and impedance characteristic in the check points of the malfunctioning electronic module and then compare data to the reference points.

Reference characteristics are measure on known-good circuit and are stored in files in PC. There is also a possibility to work without storing the reference data (using and applying the second probe in the same point on known-good board).

Assist-ASA operates with the characteristics presented in the form of graphical signatures and their corresponding numerical values (R is resistance, C is capacitance, U is voltage at the inflection point of the current-voltage characteristic). The criterion for the discrepancy of characteristics during automatic comparison is the excess of the threshold of tolerance of the measured R, C, U from the reference one. The threshold is set programmatically in percentage terms. For most cases, it is recommended to set the value of the limit deviation threshold at the level of 10–15%.

The method allows you to get information in order to determine the faulty elements on the board as well as to find breaks and short circuits of the conductors of the printed circuit board.

The Assist-ASA consists of an analysis unit and two active probes (each of them is equipped with a contact needle and a micro-circuit). The USB analysis unit is connected to a control computer (laptop) with special software installed. Assist-ASA can be equipped with optional accessories.

Characteristic tracer has a range of advantages in comparison with its analogues:

— two channels and two modes of signature comparison (comparison to reference data and comparison to known-good module of the same type) on one screen;

— high level of automation during creation of signature data base;

— automatic identification of the quality of the contact of the probe’s needle with the board;

— automatic use of three different combinations of parameters of the probe signal during the measuring of the each signature;

— automatic identification of signatures correspondence with producing sound signal;

— the criterion of signatures correspondence is managed from the interface;

— one channel (measuring the current signature, recording it to a file, comparing the current signature with the reference one from the file);

— two channels (comparing the current signature with the signature of the known-good UUT)

from 5 Ohm to 10 MOhm,

with the discreteness 1Ohm (in the range from 5Ohm to 1 kOhm), 100 Ohm (5kOhm – 1 MOhm), 100kOhm (1MOhm – 10 MOhm)

from 2 pF to 1000 mkF,

with the discreteness 1 pF (in the range from 2 pF to 1 mkF), 1000 pF (1 mkF – 1000 mkF)

Curve Tracer or Audio Analyser?

I’m now a full-time instrument maker, and thinking about how I allocate resources in 2020. I’ve been into DIY hifi since a teenager and want to resurrect two pet projects (1. Curve Tracer and 2. Audio Analyser) for my little company (Electron Plus) — thinking about which might have the most impact. Would love to hear feedback, what people are using and perhaps what’s on their wishlist. The very basic specs as I left them before I got busy with sub-contract work:

Curve Tracer
PC connected
-200 to +200V collector supply
-20 to +20V / -200mA to +200mA step generator
<1uA to >5A
Dual channel option/version
2nd step generator/SMU option/version.

Audio Analyser
2channels
Fully floating input and fully floating output sections
>+20dBV outputs
Balanced ins and outs
48/96/192 and possibly 768KHz rates

I built working prototypes of both a few years back — but would probably refresh both designs (certainly restart the digital side of things). Probably got enough resource to do one of these projects only.