Test contact connection checking method and circuit

• US 5,886,530 A
• Filed: 08/15/1997
• Issued: 03/23/1999
• Est. Priority Date: 08/15/1997
• Status: Expired due to Term

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Keithley Instruments, Inc.
• Inventors: Fasnacht, Glenn, Goeke, Wayne
• Primary Examiner(s): Do, Diep N.
• Application Number:
  US08/911,781
• Time in Patent Office: 585 Days
• Field of Search: 324/421, 324/601, 324/602, 324/609, 324/611, 324/696, 324/704, 324/705, 324/754, 324/756, 324/713, 324/715, 324/537, 324/538, 324/419
• US Class Current: 324/611
• CPC Class Codes: G01R 27/205 Measuring contact resistance of connections, e.g. of earth connections
• CPC Class Codes: G01R 31/66 Testing of connections, e.g. of plugs or non-disconnectable joints testing for incorrect line connections G01R31/55

Abstract

A contact resistance check circuit and method for verifying that a sufficient electrical connection is established between a source and a sense lead of a Kelvin connection. The circuit includes a microprocessor for driving a transformer that is connected to the source/sense probe (i.e., contact resistance) with an input pulse. The input pulse is altered in relation to the magnitude of the contact resistance to produce a check pulse. A comparator is used to compare the check pulse with a threshold voltage and for generating a fault indication signal. A flip flop then stores the fault indication signal so that the fault indication signal may be monitored by the microprocessor.

Claims

1. A method of checking a contact impedance, comprising the steps of:

providing a device under test having a contact point connected to a source lead and a sense lead, said contact impedance being the impedance from the source lead through the contact point to the sense lead;

applying a pulse to the contact impedance to create a check pulse; and

comparing the check pulse with a threshold to produce a signal indicative of a contact fault.

2. A method for checking a contact resistance, comprising the steps of:

generating a pulse by a microprocessor;

driving a transformer connected to the contact resistance with said pulse so as to create a check pulse,

generating a threshold voltage with a voltage divider;

comparing the check pulse and the threshold voltage to generate a contact fault indication signal;

storing the fault indication signal; and

monitoring the stored signal by the microprocessor.

3. The method according to claim 2, further comprising the steps of:

inverting said pulse before driving the transformer; and

inverting the fault indication signal before storing the fault indication signal.

4. The method according to claim 2, further comprising the step of filtering the check pulse with a low pass filter before the step of comparing the check pulse and the threshold voltage.

5. A contact resistance check circuit, comprising:

a microprocessor for generating a pulse;

a transformer having a primary winding connected to be driven by said pulse and a secondary winding connected to the contact resistance, said transformer/contact resistance connection altering said pulse in relation to the magnitude of the contact resistance so as to create a check pulse;

a comparator connected to compare the check pulse and a threshold voltage generated by a voltage divider, said comparator generating a contact fault indication signal; and

a flip flop connected to store the fault indication signal for monitoring by the microprocessor.

6. The circuit according to claim 5, further comprising a low pass filter connected to filter the check pulse before the comparator compares the check pulse with the threshold voltage.

7. A contact resistance check circuit, comprising:

a microprocessor for generating a pulse;

an inverter connected to the microprocessor for inverting said pulse;

a transformer having a primary winding connected to be driven by the inverted said pulse and a secondary winding connected to the contact resistance, said transformer/contact resistance connection having the effect of altering the inverted said pulse in relation to the magnitude of the contact resistance so as to create a check pulse;

a comparator connected to compare the check pulse and a threshold voltage generated by a voltage divider, said comparator generating a contact fault indication signal;

a second inverter for inverting the fault indication signal; and

a flip flop connected to the second inverter and for storing the inverted fault indication signal for monitoring by the microprocessor.

8. The circuit according to claim 7, further comprising a low pass filter connected to filter the check pulse before the comparator compares the check pulse with the threshold voltage.