US-12618873-B1 - Partailly guarded switching matrix for automatic electronic test equipment

Abstract

Systems and Methods for capacitance testing of a unit under test with parasitic capacitance directed to a guard rail. The system includes test points, wherein the plurality of test points are divided into at least two groups; a stimulus source; a first group guard relay electrically connected to each of the test points in a first; a second group guard relay electrically connected to each of the test points in a second; a guard rail coupled to the first group guard relay and the second group guard relay; a first group return relay electrically connected to each of the test points in a first group; a second group return relay electrically connected to each of the test points in a second group; a current measurement rail coupled to the first group return relay and the second group return relay; a current meter coupled to the measurement rail; and a controller.

Inventors

• DAVID ALAN SHIER
• Patrick Noll

Assignees

• DIT-MCO INTERNATIONAL LLC

Dates

Publication Date

20260505

Application Date

20251106

Claims (20)

1. 1 . A system for capacitance testing of a unit under test (UUT), comprising: a plurality of test points, each test point associated with an input relay and an output relay, such that the number of test points is equivalent to the number of input relays and the number of output relays, wherein the plurality of test points are divided into at least two groups; a stimulus source configured to provide a stimulus signal; a stimulus rail, the stimulus rail electrically connected to each of the test points via the associated input relays, wherein the stimulus rail is electrically connected to the stimulus source; a first group guard relay electrically connected to each of the test points in a first group via the associated output relays; a second group guard relay electrically connected to each of the test points in a second group via the associated output relays; a guard rail, the guard rail coupled to the first group guard relay and the second group guard relay; a first group return relay electrically connected to each of the test points in a first group via the associated output relays; a second group return relay electrically connected to each of the test points in a second group via the associated output relays; a current measurement rail, the current measurement rail coupled to the first group return relay and the second group return relay; a current meter coupled to the current measurement rail; and a controller operably coupled to the stimulus source, the input relays, the output relays, the guard relays, the return relays, and the current meter.
2. 2 . The system of capacitance testing according to claim 1 , wherein, in response to a test request between a first point in the second group and a second point in the second group, the controller is configured to: (i) actuate the input relay for the first point to a closed position and the output relay for the first point to an open position; (ii) actuate the output relay for the second group to a closed position; (iii) actuate the input relays for the test points in the first group to an open position; (iv) actuate the output relays for the test points in the first group to a closed position; (v) actuate the remaining input relays associated with test points in the second group to an open position; (vi) actuate the remaining output relays associated with test points in the second group to an open position; (vii) actuate the first group guard relay to a closed position; (viii) actuate the first group return relay to an open position; (ix) actuate the second group guard relay to an open position; (x) actuate the second group return relay to a closed position; (xi) provide a stimulus via the stimulus source; and (xii) measure a return signal with the current meter.
3. 3 . The system of capacitance testing according to claim 2 , wherein the controller is further configured to actuate all of the input relays of a group of test points not associated with a current test to an open position and all of the output relays of a group of test points not associated with the current test to a closed position.
4. 4 . The system of capacitance testing according to claim 1 , further comprising a first group stimulus relay and a second group stimulus relay; wherein the stimulus rail comprises a first group stimulus rail and a second group stimulus rail, the first group stimulus rail electrically connected to each of the input relays for the test points in the first group via first group stimulus relay, the second group stimulus rail electrically connected to each of the input relays for the test points in the second group via second group stimulus relay.
5. 5 . The system of capacitance testing according to claim 1 , the controller is further configured to implement a test by actuating a subset of input relays and a subset of output relays for only the test points associated with the measurement, leaving all other input or output relays in a state such that parasitic currents are redirected to the guard rail.
6. 6 . The system of capacitance testing according to claim 1 , wherein the number of groups is greater than two, and the system further comprises a corresponding group guard relay and a group return relay for each group.
7. 7 . The system of capacitance testing according to claim 1 , wherein the guard rail is connected to a ground.
8. 8 . The system of capacitance testing according to claim 1 , wherein each input relay and each output relay comprises a solid-state relay or an electromechanical relay.
9. 9 . The system of capacitance testing according to claim 1 , wherein there are at least eight test points.
10. 10 . The system of capacitance testing according to claim 1 , further comprising a memory element operably coupled to the controller, wherein the memory element is configured to log results of multiple capacitance measurements.
11. 11 . The system of capacitance testing according to claim 1 , wherein the system is configured to measure capacitance in picofarads.
12. 12 . A system for capacitance testing of a unit under test (UUT), comprising: a plurality of test points, each test point associated with an input relay and an output relay, such that the number of test points is equivalent to the number of input relays and the number of output relays, wherein the plurality of test points are divided into at least two groups; a stimulus source configured to provide a stimulus signal; a first stimulus rail, the first stimulus rail electrically connected to each of the test points in the first group via the associated input relays, wherein the first stimulus rail is electrically connected to the stimulus source via a first group stimulus relay; a second stimulus rail, the first stimulus rail electrically connected to each of the test points in the second group via the associated input relays, wherein the first stimulus rail is electrically connected to the stimulus source via a second group stimulus relay; a first group guard relay electrically connected to each of the test points in a first group via the associated output relays; a second group guard relay electrically connected to each of the test points in a second group via the associated output relays; a guard rail, the guard rail coupled to the first group guard relay and the second group guard relay; a first group return relay electrically connected to each of the test points in a first group via the associated output relays; a second group return relay electrically connected to each of the test points in a second group via the associated output relays; a current measurement rail, the current measurement rail coupled to the first group return relay and the second group return relay; a current meter coupled to the current measurement rail; and a controller operably coupled to the stimulus source, the input relays, the output relays, the guard relays, the return relays, and the current meter.
13. 13 . The system of capacitance testing according to claim 12 , wherein, in response to a test request between a first point in the second group and a second point in the second group, the controller is configured to: (i) actuate the input relay for the first point to a closed position and the output relay for the first point to an open position; (ii) actuate the output relay for the second group to a closed position; (iii) actuate the first group stimulus relay to a closed position; (iv) actuate the second group stimulus relay to an open position; (v) actuate the input relays for the test points in the first group to an open position; (vi) actuate the output relays for the test points in the first group to a closed position; (vii) actuate the remaining input relays associated with test points in the second group to an open position; (viii) actuate the remaining output relays associated with test points in the second group to an open position; (ix) actuate the first group guard relay to a closed position; (x) actuate the first group return relay to an open position; (xi) actuate the second group guard relay to an open position; (xii) actuate the second group return relay to a closed position; (xiii) provide a stimulus via the stimulus source; and (xiv) measure a return signal with the current meter.
14. 14 . The system of capacitance testing according to claim 13 , wherein the controller is further configured to actuate all of the input relays of a group of test points not associated with a current test to an open position and all of the output relays of a group of test points not associated with the current test to a closed position.
15. 15 . The system of capacitance testing according to claim 12 , the controller is further configured to implement a test by actuating a subset of input relays and a subset of output relays for only the test points associated with the measurement, leaving all other input or output relays in a state such that parasitic currents are redirected to the guard rail.
16. 16 . The system of capacitance testing according to claim 12 , wherein the number of groups is greater than two, and the system further comprises a corresponding group guard relay and a group return relay for each group.
17. 17 . The system of capacitance testing according to claim 12 , wherein the guard rail is connected to a ground.
18. 18 . The system of capacitance testing according to claim 12 , wherein each input relay and each output relay comprises a solid-state relay or an electromechanical relay.
19. 19 . The system of capacitance testing according to claim 12 , wherein there are at least eight test points.
20. 20 . The system of capacitance testing according to claim 12 , further comprising a memory element operably coupled to the controller, wherein the memory element is configured to log results of multiple capacitance measurements.

Description

RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63/717,797, filed Nov. 7, 2024, the content of which is incorporated herein by reference in its entirety. FIELD Embodiments herein relate to systems and methods that analyze electrical wiring harness assemblies. BACKGROUND Switching matrices are well known in the design of automatic electronic test equipment. In the case of wire/harness test systems, these matrices consist of a large number of electro-mechanical relays. Typically, two relays are required for each test point connected to the Unit Under Test (UUT). The first relay provides the stimulus output, and the second relay is used for the return side of the circuit. As these test systems utilize DC, or very low frequency AC stimulus, in order to minimize cost, the relays and the surrounding circuits are unshielded. Such designs are typical for continuity, resistance, and isolation testing. However, when measuring capacitance, the parasitic capacitance of the circuits associated with the open relays, and the isolated wiring in the UUT, can overwhelm the measurement. SUMMARY One method for reducing the effect of parasitic capacitance is to connect circuits that are to be isolated from the measurement to a guard network that connects directly to the return side of the stimulus source, bypassing the current measurement circuit. This method requires a third relay for each test point. While the result is a fully guarded network, this arrangement is typically considered prohibitively expensive, given the 50% premium in relay count simply for the single use case of capacitance measurements. Generally, there is a need to provide the ability to reduce the amount of parasitic capacitance during capacitance testing without requiring a third relay for each test point. Methods and systems to provide a level of guarding without the need for the extra relays are therefore desirable. In an embodiment, a system for capacitance testing of a unit under test (UUT), can be included having a plurality of test points, each test point associated with an input relay and an output relay, such that the number of test points can be equivalent to the number of input relays and the number of output relays, wherein the plurality of test points can be divided into at least two groups, a stimulus source configured to provide a stimulus signal, a stimulus rail, the stimulus rail electrically connected to each of the test points via the associated input relays, wherein the stimulus rail can be electrically connected to the stimulus source, a first group guard relay electrically connected to each of the test points in a first group via the associated output relays, a second group guard relay electrically connected to each of the test points in a second group via the associated output relays, a guard rail, the guard rail coupled to the first group guard relay and the second group guard relay, a first group return relay electrically connected to each of the test points in a first group via the associated output relays, a second group return relay electrically connected to each of the test points in a second group via the associated output relays, a current measurement rail, the current measurement rail coupled to the first group return relay and the second group return relay, a current meter coupled to the current measurement rail, and a controller operably coupled to the stimulus source, the input relays, the output relays, the guard relays, the return relays, and the current meter. In an embodiment, wherein, in response to a test request between a first point in the second group and a second point in the second group, the controller can be configured to (i) actuate the input relay for the first point to a closed position and the output relay for the first point to an open position, (ii) actuate the output relay for the second group to a closed position, (iii) actuate the input relays for the test points in the first group to an open position, (iv) actuate the output relays for the test points in the first group to a closed position, (v) actuate the remaining input relays associated with test points in the second group to an open position, (vi) actuate the remaining output relays associated with test points in the second group to an open position, (vii) actuate the first group guard relay to a closed position, (viii) actuate the first group return relay to an open position, (ix) actuate the second group guard relay to an open position, (x) actuate the second group return relay to a closed position, (xi) provide a stimulus via the stimulus source, and (xii) measure a return signal with the current meter. In an embodiment, the controller can be further configured to actuate all of the input relays of a group of test points not associated with a current test to an open position and all of the output relays of a group of test points not associated with the current test to a closed position. In an embo