Circuit Card Assembly is formed when components are fixed onto a PCB (Printed Circuit Board) to form a functional circuit. These are also known as PCBA (Printed Circuit Card Assembly.
CCA diagnostics describes the process of identifying the cause of a failure in the electronic circuit to a component level.
Once a fault has been identified in a circuit the Circuit Card Assembly (CCA) can be repaired by replacing the faulty component or rectifying the fault.
When a PCB (Printed Circuit Board) is loaded with compnents to form a functional circuit (PCBA or CCA) it needs to be tested to ensure it works as expected and if not to identify the cause of the failure.
The process of repairing a PCBA or CCA
The process of diagnosing the cause of a failure in a CCA or PCBA.
Once a fault has been identified in a circuit the Circuit Card Assembly (CCA) can be repaired by replacing the faulty component or rectifying the fault.
See "CCA testing".
See "Circuit card diagnostics"
One way of testing a circuit is to check the correct functionality of each component. To achieve this a test clip (see also Device Test Interface) is used to make physical electrical contact with the pins of the device so that the test signals can be applied and measured. This type of testing is commonly referred to as clip testing or fixtureless test because it doesn't require a test fixture such as a Bed-of-Nails.
This is the test process performed on an individual device. The test sequence can be performed with the device in a circuit(in-circuit test) to check its correct functionality or out of a circuit to make parametric measurements.
When an electrical circuit is used it heats up and then cools down when it is switched off. This heating and cooling can cause condensation whicih will affect the operation of the circuit. In addition if a circuit is used in an extreme environment then it can be subject to other heating, cooling, condensation and general exposure to the elements. These situations will caus the circuit to malfunction.
Applying a conformal coating, or varnish, to the circuit will protect it from this type of problem. Where a circuit is also suibject to extreme mechancial forces it may be encapsulated or "potted" to prevent the components from moving.
If physcial electrical contact is required to a component(s) in a circuit then any conformal coating must be first removed. This removal process may use chemicals or alternatively the Diagnosys CRS8000 system uses a non-hazardous abrasive media to safely remove the coating without the worry of damage to the circuit.
As component become scarce / obsolete it is unfortunately possible to source a different device, different specification, or even no device, in the same packaging. These counterfeit devices need to be identified and rejected prior to being used ina circuit where they fail or at whose cause safety issues. It is possible to perform functional checks on the components purchased to make sure they operate and perform as specified. This testing can be performed using the Diagnosys PinPoint range which then provides confidence in the devices being purchased and used.
If a device is suspected of being counterfeit, or asa confidence check, its correct fiunctionality can be tested using an out of circuit test adaptor with the Diagnosys PinPoint range of systems.
IC (Integrated Circuit) test clips are used to provide physical test access to electronic devices. When commerically available test clips are not available, or do not provide the robustness and repeated reliable contact required for testing, then a custom designed clip must be used. The Diagnosys range of robust Device Test Interfaces (DTI) provides an affordable solution for a large variety of package types and pin spacings from 0.4mm upwards, including Russian pin spacing. Custom designed DTIs are also available.
During a test sequence the measurements and test results need to be recorded. This data capture is part of the automated test process on an ATE and often referred to as data logging.
Data rate is a term used to describe the speed at which test data is applied and can be measured using a test system. It is quoted in 'Hertz' and indicates the rate at which a test pattern can be repeated.
This is the defence standard which describes the parameters to ensure the safe test of devices in a circuit.
The defence standard covering the safe testing of devices in-circuit and covering topics such as backdrive current, overshoot, undershoot and other related topics.
Repair of electronic modules and systems in a workshop.
Equipment used to test and troubleshoot electronic circuits, modules and systems in a repair workshop.
The test of a single electronic component. The component could be an active (power required to operate) digital, analog or mixed signal device or a passive (no power required) device.
When testing a single device it is necessary to make electrical contact with the pins. This is achieved using a commercial IC clip or with a robust and reliable Device Test Interface (DTI). Diagnosys provides a range of DTIs which can also be tailored for custom device package designs.
The process of testing the function of an electronic device to make sure it operates correctly and to specification.
A widely used term but in this context referring to detecting and then identifying the cause of a failure in an electronic system or circuit.
A type of testing in which each electronic device in a circuit is tested individually, or as a group, against a set of parameters to determine if it is working correctly. If a device fails the fault diagnosis can be made.
A self-contained unit which provides diagnostic tools and software for the detection and identification of faults in an electronic circuit. Diagnosys has designed the UDA (Universal Design Architecture) Diagnostis Sub System which can be integrated into a third party test system to provide the test and daignostic capabilities for electronic circuits.
The test of a circuit, module or system to identify the cause of any failure. The level of the diagnosis may be to a circuit board, a module or an individual component depending on the test approach and the capabilities available. The Diagnosys UDA system can be configured to test a module, the circuit boards it contains and also identify a failure to an individual component on a circuit. It combines multiple test methods to deliver comprehensive test coverage with excellent fault diagnostic capabilities.
A complete "turnkey" solution comprising of a test system, test interfaces and test programs to test and fault find an electronic circuit or system.
A test system that has in-built integrated test and fault finding capabilities for an electronic circuit.
The leading electronic test and fault finding company with over 40 years experience in the test, fault finding and repair of electronic circuits.
A data technology that uses discrete (discontinuous) values e.g. '1' and '0' / 'on' and 'off'. The discrete data can be applied sequentially to form a digital signal. An digital device is one that handles digital data.
The detection and identification of a fault in a digital circuit by the analysis of the data at the edge connector and / or each network of the circuit.
The creation and application of a digital signal to the inputs of a circuit such that it functions in a way that allows it to be tested and any faults detected.
The application and comparison of signals on a digital circuit, or module, such that the correct circuit function can be validated.
A Device Test Interface (DTI) provides the physical electrical connection between a test system and the device being tested. Manufactured by Diagnosys, these DTI provide a robust and reliable test initerface and can be designed to test device in custom packages. PIn spacing of 0.4mm and above can be handled as well as Russian devices.
Device Under Test - a term commonly used in the test of electronic circuits and components.
The process of testing a circuit by using the edge connectors only. This method is also commonly referred to as 'functional testing' because it tests the overall function of the circuit compared to in-circuit testing which test each individual component in the circuit.
Usually referring to a single or a set of discrete instruments used to apply or measure electrical signals. Electrical / electro-mechanical technology generally deals with generation, distribution, storage and conversion of electrical energy to and from some other forms using wires, motors, generators, batteries and other passive devices.
Electronic circuits are formed of active and passive components connected together to perform a function. Electronic diagnostic equipment is used to apply and measure electronic signals on a circuit such that a fault can be detected and then identified.
Equipment used to perfrom a repair on an electronic circuit. Such equipment might include a Coating Removal System (CRS8000) from Diagnosys, BGA re-work stations, solderinga nd de-soldering tools etc.
The process of identifying the cause of a failure in an electronic circuit. This can be achieved using a system such as the Diagnosys PinPoint system.
The ongoing support and repair of electronic system, modules and circuits. Maintenance can be pro-active by performing refurbishments or reactive when a failure occurs. Typical equipment used in a maintenance environment includes the Diagnosys S500, PinPoint, AutoPoint-DT and S790 systems.
A sub-assembly or module of a larger electronic system can be tested using the interface to the rest of the system. This functional test will determine if the module is operating correctly. A module may contain circuit boards. Should a fault be detected then the cause is diagnosed using test equipment such as the Diagnosys PinPoint system.
The repair of an electronic circuit.
A service offered for the test and repair of electronic services. Diagnosys offers this comprehensive service as part of the product range and it includes test, repair, refurbishment, obsolescence management
An electronic repair solution may consist of providing a service or equipment or a combination of both. Diagnosys can provide electronic repair solutions as a service to customers or can supply the euqipment and test programs to allow customers to achieve this themselves. A solution may involve both elements where a customer may use the equipmetna ndtest programs to determine if a circuit is faulty and then send only the faulty ones for repair at Diagnosys.
The test of an electronic circuit. This may be achieved by applying and measuring signals at the edge connector or by using in-circuit techniques. Typcal system used to achieve this include:
Functional test - Diagnosys S500, S790, PinPoint
In-Circuit test - Diagnosys S790, PinPoint, AutoPoint DT
Systems such as the Diagnosys S500, S790, PinPoint and AutoPoint DT perform tests on electronic circuits and are classed as Electronic Test Equipment.
A service provided to test and sometimes dagnose faults in electronic circuits. Diagnosys offers this service.
A complete solution for the test of electronic circuits and could mean using an elelctronic test service or purchasing the equipment test interfaces and test programs to perfrom the function in-house. Diagnosys has a range of services and equipment and is ideally placed to provide these solutions.
Electronics is the science of using passive and active components connected together in a circuit to perform a function e.g. amplifier, radio, computer etc.
Electrical / electro-mechanical technology generally deals with generation, distribution, storage and conversion of electrical energy to and from some other forms using wires, motors, generators, batteries and other passive devices.
Membain and Factron were names integrated into the Schlumberger Board Test business but which are now part of the Diagnosys Group.
The process of detectinig and identifying the cause of a dailure in an electronic circuit.
A fault dictionary contains a list of possible faults in a circuit and the output pattern, or fault signature, each causes on the outputs of the circuit. Fault dictionaries are created by logic simulators or can be learnt manually and provice faster fault diagnostics.
A system used to find faults in an elelctronic circuit, see also FaultFinder.
The process of finding a fault in an electronic circuit. This can be achieved using the Diagnosys PinPoint or AutoPoint DT systems or more slowly manually.
A list of the faults possible in an electronic circuit, for example; open circuit, short circuit, stuck at 1, stuck at 0, etc.
The brand name for the Diagnosys FaultFinder series of equipment.
A self-contained bench-top unit in the Diagnosys FaultFinder range of systems. It uses V/I techniques (analog signatures) to test and detect failures in a circuit and has a built-in multiplexer.
A test perfromed at the end of a manufacturing or repair process to prove a circuit, module or system is working.
The process of detecting and then identifying the cause of a failure in a PCB (Printed Electronic Circuit).
The basic maintenance or repair performed on an equipment while it is in its normal operating environment, a term generally associated with defence organisations.
The basic repair that can be perfromed on an equipment or module while it it in its normal operating enviroment.
The test of a circuit / PCB without having to use a dedicated test fixture and normally meaning clip testing or testing using a DTI (Device Test Interface).
The Diagnosys AutoPoint DT is an example of a flying probe system where the test contact is supported on an X-Y-Z table and automatically probes the circuit according to pre-learnt data. The systems generally use VI (analog signature) tecniques to test the circuit.
Maintenance of an electronic circuit or module in an well equiped workshop supported by the Original Equipment manufacturer. Repairs at this level will go to component level if possible.
The repair of an electronic circuit or module by the OEM (Original Equipment Manufacturer).
The repair of an electronic circuit or module by the OEM (Original Equipment Manufacturer).
Functional board test uses the edge connectors of a PCB to validate the correct operation of the circuit. Diagnosys systems that perform functional test include the S790, S500 and PinPoint systems.
The test of an electronic module, or box, using the external connectors to validate the correct operation.
When a circuit or module is tested functionally and fails then the fault has to be diagnosed. This can be achieved using a guided probe to automatically backtrack through the circuit and comparing good data (simulated or learnt, digital or analog) with actual data for each network probed. It is also possible to probe manually with a skilled operato determining the probe points or using a manually generated fault tree. Diagnosys systems supporting automatic guided probing include S790 and PinPoint.
The test of a PCB, circuit or module from the edge connectors to ascertain the working state.
The test of a module using the edge connectors to validate its functionality.
The test of a system, module, assemble or PCB to vallidate its correct function. A typical functional test system is the Diagnosys S790, S500 and PinPoint UDA system.
GPATE (General Purpose Automatic Test Equipment) describes a test system that can be used to test different types of circuits and modules rather than being dedicated to one type of module, assembly or circuit. A test system dedicated to a single circuit is called a Special to Type Test Equipment (STTE).
The "Gold Disc" programme is a US defense initiative to ensure golden (known good and proven) test programs are used throughout the organisation. It is a form of version control and prevents tampering with proven test programs.
General Purpose Electronic Test Equipment is an equipment that can be used to test and fault find multiple electronic circuits and modules.
Government Supply Agency Contract ensures that the US government is procurring items at the best commercial rates.
Part of a test program debug process in which guards (static electronic signals) are applied for the duration of a test to stop interference from other devices. It is only applicable to in-circuit testing and applies to active and passive device tests.
If a functional test fails then a guided probe is used to access signals internally in the circuit. At each probe point the diagnostic software makes a decision on whether a reliable fault diagnosis can be made or whether more information is needed. If more infomation is needed then the software will determine the next probe point and will guide the operator accordingly. However, the probe can also be used manually with a skilled operator or a manually created fault-tree. Diagnosys systems supporting automatic guided probe diagnostic include the S790 and PinPoint systems.
Input and Output (I/O), a common term used to describe the input and output connectors of a device or circuit.
IC (Integrated Circuit) test descibes the testing of a single electronic device or component.
IC (Integrated Circuit) test clips are used to provide physical test access to electronic devices. When commerically available test clips are not available, or do not provide the robustness and repeated reliable contact required for testing, then a custom Diagnosys DTI (Device Test Interface) can be used.
In-Circuit Test (ICT) referes to the test nethod where each component of a circuit is tested individually while in the circuit. This can be achieved using a Bed-of-Nails fixture or by fixtureless techniques by using test clips and DTIs.
In-Circuit Test (ICT) Manufacturing Defects Analysis (MDA) is a test technique commonly used in a manufacturing process to detect any faults introdcude by the process itself such as short circuits, open circuits, incorrect orientation or wrong device fitted. It assumes that devices are working and that any faults, or defects, have been introduced by the manufacturing process.
In-Circuit Test and Measurement.
Impedance analysis is a test technique where the impedance characteristic of a network are learnt from a known good circuit and then stored as part of a test program. The impedance characteristic is created by applying an analog signal, usually a sinusoidal signal, and then measuring the current at points on the signal. These Voltage (V) and Current (I) measurements are commonly refered to as VI, V/I or V-I signatures.
Using an in-circuit test method and diagnostic software to identify the cause of faults in a circuit.
The test method where each component is tested individually while in a circuit. Test access is achieved either through a BoN (Bed-of-Nails), test clip or robust Device test Interface (DTI).
Part of a manufacturing process where a component or circuit is tested in the production line, or in-line.
Interface test adaptor is the test fixture for a specific circuit board (PCB) or module. It provides the physical interface between the mass interconnect connection of the test system and the UUT (Unit Under Test).
The maintenance of an electronic circuit or module that can be performed in a workshop situated between the normal operating environment and a fully equipped depot or base workshop. It usually involves the test and replacement of individual circuits but not repair to a component level.
Joint Test Action Group was formed to develop and promote Boundary Scan test techniques. The group formed the IEEE 1149.1 standard first defining the application of Boundary Scan techniques and has gone on to develop and promote other related standards. Boundary Scan testing is often referred to as JTAG testing.
A logic simulator that is well established in the defence electronics test environment. It is a trade mark of Teradyne Inc.
The moving of test programs from a legacy, or obsolete, test system to a new test platform. Replacing the host platform for the test program.
Old or obsolete test systems and equipment.
Lower Level Replaceable Unit - an assembly or circuit that can be replaced in a module or Line Replaceable Unit (LRU).
A software tool that models the operation of an electronic circuit. Test vectors, or inout stimulus can be created and executed against the model to predict the output vectors (patterns) and the activity at each internal network. The simulator can also create a list of possible faults in the circuit (Fault List) and then determine the effectiveness of the test program at finding these faults (Comprehensiveness of the program). When the program is at a suitable stage the simulator can be used to try each of the possible faults in turn against the program and record the fault signature (output pattern) finthe Fault Dictionary.
Line Replaceable Unit - a module on assemble that can be replaced in the main equipment / system.
The test of an LRU (Line Replaceable Module) using the edge connectors where the test system will stimulate and measure responses from the unit.
The test of a circuit, module or final system during the manufacturing process.
Manufacturing Defects Analyser (MDA) used to test for errors and problems in the manufacturing process of an electronic circuit / PCB. Typical faults include open and short circuits, incorrect orientation, wrong component. Diagnosys systems that have an MDA capability include the S790, PinPoint and AutoPoint DT.
A test system specifically designed to perform Manufacturing Deefects Analysis tests. Diagnosys systems with this capability include the S790, PinPoint and AutoPoint DT.
One of the founder companies of automated functional test equipment. Diagnosys now has the IPR and expertise to support these legacy systems and provide re-hosting services to newer test platforms.
A test platform that can support both digital, analog and mixed digital / analog circuits. Diagnosys system that support mixed signal testing include; S790, S500, PinPoint.
The test of an electronic module or assemble using the edge connectors. The test system will provide the stimulus and measure the response of the module.
The Netlist is a description of the interconnections between the components on a circuit (PCB). The netlist can be created manually form the circuit diagram, imported from a CAD (Computer Aided Design) or learnt from a known good circuit.
The process which determines and monitors the availability of electronic components so that obsolescence issues can be identified and plans made to negate the issues. Sometimes this involves the re-engineering of parts of a circuit.
The inability to source new electronic components or provide support for an equipment.
Performing test and diagnostics for an electronic circuit off of the production line.
The maintenance of an electronic circuit that can be performed in the normal operating environment.
PinPoint II R system (P2R) the second generation Diagnosys PinPoint system that is RoHS (Reduction of Hazardous Substances) compliant.
Test equipment that can be used with a PC, for example the Diagnosys FaultFinder PCI card and FaultFinder VIP that can be used with a PC turning it into a test equipment.
Printed Circuit Board (PCB) diagnostics, or fault finding. The process of finding the cause of a failure on a circuit or PCB.
The test of a Printed Circit Board using the edge connectors and verifying the fucntionality.
The process of repairing a Printed Circuit Board by rectifying any faults diagnosed.
Similar to PCB repair but more generally applicable to a new board.
The test, fault detection and identification of a Printed Circuit Board. The test could be functional, in-circuit, boundary scan, VI.
A test equipment that is designed to automatically test a Printed Circuit Board.
A range of electronic circuit test and fault finding systems designed and manufactured by Diagnosys.
One of the Diagnosys PinPoint range of products.
A variant of the PinPoint II R systems and part of the PinPoint range of products from Diagnosys.
A fault finding and test system for electronic PCBs designed and built by Diagnosys
Based on Universal Design Architeture the PinPoint UDA system is a module, circuit card and component test and fault finding system. It is part of the Diagnosys PinPoint range of test systems.
The process of fault finding an electronic circuit (PCB). The PinPoint range of system and the AutoPoint DT are excellent PCB test and Diagnostic systems.
The test of an electronic PCB to verify its function. The S790, S500, Pinpoint and AutoPoint DT systems provide this capability.
Finding the cause of a failure in an electronic circuit card or PCB. The PinPoint range of systems from Diagnosys are excellent for troubleshooting Printed Circuit Cards (or PCBs)
Testing an electronic circuit or module during the manufacturing or production process. The S790, S500, PinPoint and AutoPoint DT can all be used for production testing depending on the application and volumes.
Generally referring to test equipment that has been designed specifically for higher volume manufacturing environments. See also MDA systems.
The provision of services to create test programs for test systems (ATE). Diagnosys offers a range of services which includes test programming services.
PCI Extensions for Instrumentation (PXI) defines a standard for modular instrumentation. PXI instruments are used in the Diagnosys S500 and PinPoint systems.
A term used to commonly describe an early type of test equipment that was mounted in an industry standard 19" rack and instruments were "stacked" in the rack. The term is still used sometimes to loosely describe todays more integrated and designed functional test solutions.
When a BGA device fails or has a soldering fault then it must be removed from the circuit. Prior to re-fitting the BGA it has to be re-balled with balls of solder so that it can be connected to the circuit.
The term is generally used to describe the process of creating a netlist and a circuit schematic form a physical circuit. The Diagnosys PinPoint performs thisautomatically guiding the user to move clips around the circuit as it learns the interconnections.
Part of the reverse engineering process where the netlist, or list of interconnections is learnt, prior to creating the schematic.
The process of creating the circuit schematic from a physical circuit.The Diagnosys PinPoint has this capability.
Radio Frequency (RF) test - performing a set of electronic tests on a circuit designed to work at RF frequencies. The Diagnosys S500, S790 and PinPoint UDA systems can be configured to have this capabillity.
A complete test solution involving RF (Radio Frequency) circuits. The solution includes test system, test program and fixturing.
See RF Test
A manually held or automatic probe that can be used to access networks on a circuit.
A functional test system designed by Diagnosys that can be configured to test electronic modules and circuits. Several differnet types of circuit can be supported by one system.
A legacy test system which is now superceeded by the PinPoiint range. Diagnosys has the ability to re-host test programs.
A multi-strategy high performance test system for mission and safety critical applications. The system is supported and developed by Diagnosys.
The latest variant of the S790 high performance test system from Diagnosys. Supporting multiple test strategies which include; functional, in-circuit, boundary scan, ananlog, mixed signal and RF the system is a cornerstone for many test and repair environments.
A predecessor of the S790 Series 2 test system
Part of the S790 family that has now evolved to the S790 Series 2 system.
The creation of an electronic schematic diagram from a physical circuit.
See 2nd line or intermediate line maintenance
See 2nd line or intermediate line repair
The routing of signals within an ATE. The S790, S500 and PinPoint systems all have dedicated signal switching resources. In this way analog sgnals can be routed to various points on the UUT (Unit Under Test)
The creation of a Cyclic Redundancy Code signature using the data changing on a network. The data clocks a register with feedback which then produces a count that can be expressed as a hexadecimal number. The number is stored as part of the test program and used to determine if the data on the network is correct.
The rate of change of a test channel is described as the slew rate and expressed in volts per micro second.
Shop Replaceable Assembly (SRA), a term used by the US defense organisations.
Shop Replaceable Assembly (SRA) testing using the edge connector to validate the operation of the circuit.
Shop Replaceable Unit (SRU), an electronic circit that can be replaced in a workshop. A defense related term.
The testing of a Shop Replaceable Unit (SRU)
A way to achieve the physical test connection between a test systems and an indvidual device. An alternative robust and reliable test interface is available using the Diagnosys DTI (Device Test Interface)
A set of test resources designed and assembled to perform the test and fault finding of electronic circuits.
The physical connection between a test system and the UUT (Unit Under Test)
The creation of a set of stimulus and responses for the test of an elelctronic circuit or module. This often involves the debug of the test program against the physical UUT.
See test program development.
The service offered by Diagnosys to create test programs and also supplied as part of a test solution.
The speed at which test data is applied to and received from a UUT
The provision of services to test electronic circuits and modules. Diagnosys has a range of services it offers which includes testing circuits and modules.
A complete solution for the test of electronic circuits and could mean using an elelctronic test service or purchasing the equipment test interfaces and test programs to perfrom the function in-house.
The rate at which data and signals are applied to and received from a UUT.
The input signals applied to an UUT. These are created manually by a skilled technician or engineer and structured so that they exercise the circuit under test so that the function can be verified and any faults detected.
A set of test resources designed into a single platform so that a circuit or module can be tested and faults detected.
Equipment used for the test and fault detection in electronic circuitsor modules.
The in-depth maintenance of an electronic equipment or circuit in a workshop.
The in-depth repair of a circuit or electronic module in a base workshop.
Test Program Set (TPS) development is the creation of a complete package for the test of a circuit or module. It can include the test program, the test fixture and documentation - everything that enables the UUT to be tested.
The test, fault finding and repair of elelctronic modules and circuits related to trains. The S500 system is used by major rail and mass transit authorities and organisations for the support of electonic modules such as door controlers, HVAC, ATO etc.
The process of fault finding an electronic or electrical system.
The process of fault finding an electronic circuit or module.
Identifying an electronic fault to the component causing the failure.
A term used to describe a complete solution that is ready to use and generally includes a test system, test programs, test fixtures and documentation.
Universal Design Architecture (UDA) is a flexible and powerful system architecture which is based on the PinPoint II R hardware. It enables the following implementations of the systems:
UDA System - a complete flexible test system for the test of modules and PCBs with integrated diagnostic capabilities.
UDA Diagnostic Subsystem - for integration into third party test systems to provide a diagnostic capability.
Unit Under Test (UUT) describes the electronic module or circuit that is being tested.
Short form expression for Voltage / Current analog signature testing. This is a power-off test technique in which the voltage and current response of a network are measured and displayed as a Lissajous figure.This impedance characteristic is stored as part of a test program. These Voltage (V) and Current (I ) measurements are commonly refered to as VI, V/I or V-I signatures
Very high speed integrated circuits Hardware Description Language (VHSIC HDL --> VHDL) is a hardware description language used in electonic design automation to describe digital and mixed-signal circuits.
A logic simulator that uses VHDL models to build a software model of a circuit. This software model can then be used to predict the behaviour of a circuit to applied stimulus.
See "Impedance signatures" and "V/I"
See "Impedance signatures" and "V/I"