Safety switch with imbalance test

Patent metadata

Field	Value
Publication number	US-10072997-B2
Application number	US-201715592399-A
Country	US
Kind code	B2
Filing date	May 11, 2017
Priority date	Nov 17, 2015
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

An apparatus for an imbalance test includes a strain measurement module that measures a strain voltage across terminals of a strain gauge. The strain voltage is representative of an amount of force on the strain gauge. The apparatus includes a test measurement module that measures a test voltage across the terminals of the strain gauge while a test resistor is connected in parallel with a resistor of the strain gauge. The test resistor is connected while the test measurement module measures the test voltage and is disconnected while the strain module measures strain voltage. The apparatus includes an average module that calculates an average strain voltage from two strain voltage measurements. The strain voltages are measured preceding and after the test voltage measurement. The apparatus includes a difference module that determines a difference voltage. The difference voltage is a difference between the average strain voltage and the test voltage.

First claim

What is claimed is:

1. An apparatus comprising:
a strain measurement module that measures a strain voltage across terminals of a strain gauge, the strain voltage representative of an amount of force on the strain gauge;
a test measurement module that measures a test voltage across the terminals of the strain gauge while a test resistor is connected in parallel with a resistor of the strain gauge, the test resistor connected while the test measurement module measures the test voltage and disconnected while the strain module measures strain voltage;
an average module that calculates an average strain voltage from two strain voltage measurements, the strain voltages measured preceding and after the test voltage measurement;
a difference module that determines a difference voltage, the difference voltage comprising a difference between the average strain voltage and the test voltage;
a difference average module that determines an average difference voltage from a plurality of difference voltages measured by the difference module;
a difference limit module that compares the average difference voltage and a difference threshold; and
a difference alert module that sends an alert if a magnitude of the average difference voltage is greater than the difference threshold,
wherein said modules comprise one or more of hardware circuits, a programmable hardware device and executable code, the executable code stored on one or more computer readable storage media.

2. The apparatus of claim 1 , wherein the test measurement module and the strain measurement module alternate measurements of voltage across terminals of the strain gauge for a plurality of measurements and wherein, for each test measurement, the average module calculates an average strain voltage from two strain voltage measurements measured preceding and after a particular test voltage measurement and wherein the difference module determines a difference voltage corresponding to each test voltage, each difference voltage comprising a difference between the average strain voltage of the strain voltage measured before the particular test measurement and the strain voltage measured after the particular test measurement.

3. The apparatus of claim 2 , further comprising:
a strain average module that determines an average strain voltage from a plurality of strain voltages measured by the strain measurement module, wherein the average strain voltage transmitted to a strain monitoring device.

4. The apparatus of claim 1 , wherein, for each strain voltage measurement, the strain measurement module measures voltage of the strain gauge a plurality of times and averages the plurality voltages to determine the strain voltage, and wherein, for each test voltage measurement, the test measurement module measures voltage of the strain gauge a plurality of voltages and averages the plurality voltages to determine the test voltage.

5. The apparatus of claim 4 , wherein the plurality of voltages measured by the strain measurement module comprises three voltages and wherein the plurality of voltages measured by the test measurement module comprises three voltage measurements.

6. The apparatus of claim 4 , wherein the test measurement module and the strain measurement module alternate measurements of voltage of the strain gauge at a measurement sample rate and a rate of measurement of voltages by the strain measurement module for each strain voltage and by the test measurement module for each test voltage is much less than the measurement sample rate.

7. The apparatus of claim 1 , wherein the test measurement module and the strain measurement module alternate measurements of voltage of the strain gauge at a measurement sample rate during an imbalance test, wherein the imbalance test results in a plurality of test voltage measurements and strain voltage measurements of a cycle of a fundamental frequency of power provided to the apparatus comprising the strain gauge.

8. The apparatus of claim 7 , wherein a length of time of the imbalance test is within 10 percent of a cycle of the fundamental frequency.

9. The apparatus of claim 1 , further comprising:
a test activation module that connects the test resistor after the strain measurement module measures strain voltage and prior to the test measurement module measuring a test voltage; and
a test deactivation module that disconnects the test resistor from the resistor of the strain gauge after the test measurement module measures the test voltage and prior to the strain measurement module measuring a next strain voltage.

10. The apparatus of claim 9 , wherein the test activation module connects and the test deactivation module disconnects a first test resistor in parallel with a first resistor of the strain gauge during a first imbalance test and connects and disconnects a second test resistor in parallel with a second resistor of the strain gauge during a second imbalance test, wherein each of the first imbalance test and the second imbalance test comprise a plurality of test voltage measurements and strain voltage measurements.

11. The apparatus of claim 1 , wherein the strain gauge measures force of a cable pull switch.

12. A method comprising:
measuring a strain voltage across terminals of a strain gauge, the strain voltage representative of an amount of force on the strain gauge;
measuring a test voltage across the terminals of the strain gauge while a test resistor is connected in parallel with a resistor of the strain gauge, the test resistor connected while measuring the test voltage and disconnected while measuring the strain voltage;
calculating an average strain voltage from two strain voltage measurements, the strain voltages measured preceding and after the test voltage measurement;
determining a difference voltage, the difference voltage comprising a difference between the average strain voltage and the test voltage;
determining an average difference voltage from a plurality of difference voltages;
comparing the average difference voltage and a difference threshold; and
sending an alert if a magnitude of the average difference voltage is greater than the difference threshold.

13. The method of claim 12 , further comprising alternating measurements of test voltage and strain voltage for a plurality of measurements and wherein calculating an average strain voltage comprises, for each test measurement, calculating an average strain voltage from two strain voltage measurements measured preceding and after a particular test voltage measurement and wherein determining a difference voltage comprises determining a difference voltage corresponding to each test voltage, each difference voltage comprising a difference between the average strain voltage of the strain voltage measured before the particular test measurement and the strain voltage measured after the particular test measurement.

14. The method of claim 12 , wherein, for each strain voltage measurement, further comprising measuring voltage of the strain gauge a plurality of times and averaging the plurality voltages to determine the strain voltage, and wherein, for each test voltage measurement, further comprising measuring voltage of the strain gauge a plurality of voltages and averaging the plurality voltages to determine the test voltage.

15. The method of claim 12 , further comprising:
connecting the test resistor after measuring strain voltage and prior to measuring a test voltage; and
disconnecting the test resistor from the resistor of the strain gauge after measuring the test voltage and prior to measuring a next strain voltage.

16. A cable p

Assignees

• Rockwell Automation Tech Inc

Inventors

• Bubar Todd
• Tsang Andrew L
• Sacherski Burt
• Tambeau Steven Robert
• Ananthanarayanan Arvind
• Dogul James Edward
• Wolfe Timothy P

Classifications

• G08B29/185

  Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system · CPC title

• G01L1/225

  Measuring circuits therefor · CPC title

• H01H17/16

  having a single flexible operating part adapted for pulling at one end only · CPC title

• H01H2235/01

  Spiral spring · CPC title

• G01L5/10 Primary

  using electrical means · CPC title