Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
  • G01R27/08—Measuring resistance by measuring both voltage and current

Definitions

• the present disclosure relates to resistance measurements. More particularly, the present disclosure relates to methods of making in-situ resistance measurements and methods for monitoring equipment based on the measurements. For example, the present disclosure can relate to methods of measurements on a resistive heating element while operating in a furnace and to real-time diagnostics and predictive failure mechanisms.
• An exemplary embodiment of a method to determine an instantaneous resistance value of an electric circuit comprises measuring an in-situ instantaneous voltage of the circuit, measuring an in-situ instantaneous current of the circuit, and calculating the instantaneous resistance based on the measured in-situ instantaneous voltage and the measured in-situ instantaneous current.
• Another exemplary embodiment of a method to determine an instantaneous resistance value of an electric circuit comprises measuring an in-situ instantaneous voltage of the circuit, measuring an in-situ instantaneous current of the circuit, measuring an in-situ instantaneous temperature of the circuit, and calculating the instantaneous resistance based on the measured in- situ instantaneous voltage and the measured in-situ instantaneous current and relating the calculated instantaneous resistance to the measured temperature.
• An exemplary embodiment of a measurement system comprises a circuit to be measured, an EI measurement module, and a controller, wherein the EI measurement module is operatively connected to the circuit to be measured to measure an in-situ instantaneous voltage of the circuit and to measure an in-situ instantaneous current of the circuit, wherein the EI measurement module is operatively connected to the controller to communicate a measurement to the controller, and wherein the measurement system calculates an instantaneous resistance based on the measured in-situ instantaneous voltage and the measured in-situ instantaneous current.
• FIG. 1 depicts an exemplary measurement technique applied to a phase angle fired load.
• FIG. 2 illustrates an example phase angle measurement pattern over a set of cycles.
• FIG. 3 depicts an exemplary measurement technique applied to a zero-cross (time proportioned) load
• FIG. 4 illustrates an example zero-cross fired measurement pattern over a set of cycles.
• FIG. 5 is a block functional diagram representing an exemplary embodiment of a measurement system.
• AC voltage is typically a circular function where the instantaneous voltage is approximately the Peak Voltage multiplied by the sine( ⁇ ) where ⁇ is in radians and a complete AC cycle (encompassing both the positive and negative half cycles) occurs over a period of 2 ⁇ radians or 360 degrees.
• An exemplary method to determine an instantaneous resistance value of an electric circuit comprises measuring an in-situ instantaneous voltage of the circuit and measuring an in- situ instantaneous current of the circuit. Based on the measured in-situ instantaneous voltage and the measured in-situ instantaneous current, the instantaneous resistance is calculated. The measured in-situ instantaneous voltage and the measured in-situ instantaneous current are measured simultaneously.
• the reference point is a zero crossing point of an AC waveform.
• the predetermined time is about 6,250 ⁇ sec ( ⁇ 10%). In a still further exemplary embodiment, the predetermined time is at or after a peak voltage value has occurred in the cycle.
• An exemplary method to determine an instantaneous resistance value of an electric circuit can optionally comprises verifying a presence of voltage in the circuit prior to measuring. Verifying the presence of the voltage contributes to avoiding erroneous measurement which would occur by including a measurement when the circuit is idle to the averaging process. Verifying can be done by, for example, a comparator circuit, either a separate circuit or incorporated into the voltage input section of the EI measurement module or into another module. In one exemplary method, a delay is implemented between verifying and measuring to avoid noise in the measurement. An example of a suitable delay is about 1,000 ⁇ sec ( ⁇ 10%). [0021] As used herein, all measurements are taken during normal operating conditions by simultaneously sampling the instantaneous voltage and current values.
• an exemplary method to determine an instantaneous resistance value of an electric circuit comprises measuring an in-situ instantaneous voltage of the circuit, measuring an in-situ instantaneous current of the circuit, and measuring an in-situ instantaneous temperature of the circuit. The instantaneous resistance based on the measured in-situ instantaneous voltage and the measured in-situ instantaneous current is calculated and the calculated instantaneous resistance is related to the measured temperature.
• the measured in-situ instantaneous voltage, the measured in-situ instantaneous current, and the measured in-situ temperature are measured simultaneously.
• the method is similar to that described herein above.
• the measurement can be taken at by a thermocouple positioned proximate the circuit.
• EXAMPLE A circuit for a heating element is electrically connected to a power supply to supply 120 vac at 60Hz to the circuit.
• a sync event is generated at the AC zero- crossing point and the measurement is taken after a period determined by an adjustable time delay. This insures that the measurements are always taken at the same point in time during the AC cycle and allows optional averaging over time of consecutive measurements.
• the measurement window is designed to be very small, e.g., less than 1%, (in one exemplary embodiment) as compared to the AC half-cycle so as to minimize the effects of the varying AC voltage during the measurement period.
• an exemplary embodiment has a 50 ⁇ sec measurement window for an AC half-cycle of 8,333 ⁇ sec for 60Hz and has a 50 ⁇ sec measurement window for an AC half-cycle of 10,000 ⁇ sec for 50Hz.
• the cycle time(/ O ⁇ + t ojr ) is equal to 20 cycles or 333 msec.
• the minimum applied power in this case is usually 1/20 or 5% as can be seen in the following equation: fzcc Von ⁇ off ) - . , l °" ⁇ £ t ⁇ ZJ - '"/ " 1 ⁇ n ZJ - f ⁇ ⁇ 0 " ' t °ff ) ⁇ 5 ° / ⁇ t on + o ff 60/fe W 60HZ
• any application of power to the resistive load creates a measurable (at least half- cycle) event.
• the preferred measurement point for zero-cross fired elements is at the peak of the AC half-cycle which occurs 4,167 ⁇ sec after the zero-cross event for a 60 ⁇ z AC source.
• the (change in voltage over time) is at a minimum, yielding the most stable dT measurements.
• phase-angle controlled loads delaying the point at which the voltage is applied to the load proportions each AC half cycle.
• the portion of the AC cycle during which voltage is applied to the load is commonly referred to as the conduction angle while the point that the conduction angle begins is referred to as the phase angle.
• the conduction angle encompasses the portion of the AC cycle from the phase angle to the next zero-crossing event. Since R is constant with respect to E and I and I is a function of E (the load is primarily resistive in this
• the percentage of power can be expressed as — h 2_ 2r .
• the percentage of power can be expressed as — h 2_ 2r .
• E waveform of the voltage is irregular, a more accurate representation of the power can be obtained by integrating the voltage over time.
• the percentage of power then becomes:
• Sync pulses can be generated by monitoring the AC supply before the energy regulation devices in the circuit.
• this monitoring point can be a pair of SCRs connected in parallel opposition.
• the incoming voltage is tested to verify power has been applied.
• the instantaneous voltage is equal to approximately 40% of the peak voltage.
• the exemplary system internally generates it's own period sync pulses to sample the voltage and current multiple times and average the readings. There is no issue with taking DC measurements on this system since it essentially measures peak values anyway.
• FIG. 1 depicts an application of an exemplary measurement technique applied to a phase angle fired load.
• an AC power supply 10 having a line frequency of 60Hz that is sinusoidal in shape, has a mean voltage 12 of 0 volts with recurring zero-crossing points 14a, 14b, 14c.
• the AC power supply 10 consists of half-cycle portions 16a, 16b that are 180 degrees or 8,333 ⁇ sec in length and having a peak voltage 18 occurring at 90 degrees or 4,166 ⁇ sec after the zero crossing points.
• the half-cycle portions 16a, 16b are proportioned such that the angle of conduction 20a, 20b produce a desired output power.
• the desired output power can be at least 10% of the maximum power.
• the proportioning of power is accomplished by delaying the firing angle 22 to approximately 133.4 degrees or 6176 ⁇ sec in the case of 10% power output. Measurement synchronization occurs from the zero crossing points 14a, 14b, 14c.
• Other desired output power can be selected, such as 2%, 3%, 8%, 15%, 25%, 30%, 50%, 60%, 80% and more.
• FIG. 2 illustrates an example phase angle measurement pattern over a set of cycles.
• the multiple consecutive AC cycles 100a, 100b, 100c have multiple zero crossing points 102a, 102b, 102c, 102d, 102e, 102f, 102g and multiple conduction angle events 104a, 104b, 104c, 104d, 104e, 104f.
• the firing angle 106a, 106b is 133.4 degrees or 6,176 ⁇ sec yielding angles of conduction 104a, 104b, 104c, 104d that produce an output power of approximately 10% of the maximum available power.
• voltage is present at the test points 108a, 108b and therefore after delays 110a, 110b a subsequent measurement 112a, 112b is taken.
• the firing angle 106c is 143.8 degrees or 6,657 ⁇ sec yielding angles of conduction 104e, 104f that produce an output power of approximately 5% of the maximum available power.
• voltage is not present at the test point 108c and therefore no measurement is attempted.
• the result of this method is that voltage and current measurements are taken simultaneously at consistent points during the AC cycles allowing subsequent measurements to be averaged over time to reduce noise since the instantaneous voltage is consistent at the point of measurement.
• each of the delay parameters may be adjusted and therefore power levels of less than 10% could be accommodated if desired. Conversely, a higher minimum measurable power level could be selected or a shorter noise delay implemented to take ⁇ V measurements where the rate of change ( ) is at a lower value, which could also increase ⁇ T overall accuracy. In addition, in cases where the line frequency is different, such as 50Hz, the time delays can be adjusted appropriately.
• FIG. 3 depicts an exemplary measurement technique applied to a zero-cross (time proportioned) load.
• the voltage is zero cross fired.
• An AC power supply 200 having a line frequency of 60Hz that is sinusoidal in shape is shown. The AC power supply
• the 200 has a mean voltage of Ov with recurring zero-crossing points 202a, 202b, 202c with half- cycle portions 204a, 204b that are 180 degrees or 8,333 ⁇ sec in length and having a peak voltage 206 occurring at 90 degrees or 4,166 ⁇ sec after the zero crossing points.
• the proportioning of power occurs by selectively applying voltage on alternate cycles or half-cycles over time. Measurement synchronization occurs from the zero crossing points 202a, 202b, 202c. The presence of voltage is tested at the zero crossing point 202a. After a delay 208, the voltage is sampled during sampling period 210. Here, a delay 208 of 4,166 ⁇ sec and a sampling period 210 of 50 ⁇ sec are shown. At the time of sampling, the measured voltage is at approximately 100% dV of its peak value, at which point the change in voltage ( ) is approximately zero. dT
• the current is measured such that the instantaneous values are taken at the same point in time. Division of the voltage measurement by the current measurement yields the instantaneous resistance measurement.
• FIG. 4 illustrates an example zero-cross fired measurement pattern over a set of cycles.
• multiple consecutive AC cycles as described in FIG. 3 are shown.
• the multiple consecutive AC cycles 300a, 300b, 300c have multiple zero crossing points 302a, 302b, 302c, 302d, 302e, 302f, 302g with voltage proportioned over time.
• voltage has been selectively applied to the load.
• subsequent measurements 304a, 304b are taken at the peak of the half-cycles at the peak voltage 306.
• the peak dV voltage is 169.7 volts and the change in voltage ( ) is approximately zero.
• An exemplary measurement system comprises a circuit to be measured, an EI measurement module and a controller.
• the EI measurement module is operatively connected to the circuit to be measured to measure an in-situ instantaneous voltage of the circuit and to measure an in-situ instantaneous current of the circuit.
• the EI measurement module is also operatively connected to the controller to communicate the measurements to the controller for further analysis.
• the measurement system calculates an instantaneous resistance based on the measured in-situ instantaneous voltage and the measured in-situ instantaneous current.
• An optional temperature measurement module can be included in the exemplary measurement system. The temperature measurement module is operatively connected to the circuit to measure instantaneous temperature.
• FIG. 5 is a block functional diagram representing an exemplary embodiment of a measurement system 400.
• the dashed components 402, 404, 406, 408 are part of the circuit being measured, which itself is part of a larger system such as a heating element or thermal processing system.
• the dashed components 402, 404, 406, 408 are representative in nature, are not inclusive of the measurement system, per se, and are included in FIG. 5 to show the interface of the measurement system 400 to the system under measurement.
• an AC voltage 402 is reduced to a desirable voltage and isolated from the load by transformer 404.
• the reduced voltage is proportioned to the resistive load 408 by the power-proportioning device 406.
• the measurement system 400 consists of an EI (voltage - current) measurement module 410 comprised of a sync input detector 412 that monitors the reduced voltage prior to the power-proportioning device 406.
• the sync input detector detects the zero-crossing event to which all of the subsequent timing is related.
• the voltage input section 414 both provides confirmation of the signal voltage being present via a comparator and the actual signal conditioning for the voltage input measurement.
• Instantaneous current input is obtained by current input section 416 from the current transformer 418 (or alternately a resistive shunt - not shown).
• the dual S & H circuit (sample and hold circuit) 420 simultaneously measures the instantaneous voltage and current signals and provides its output to the A/D converter 422.
• a micro controller 424 performs the resistance calculation as well as all measurement timing, scaling and communications to the main controller 430 across a galvanic isolation barrier 440 via communications bus 450.
• Optional temperature measurements are synchronously measured by the temperature measurement module 460.
• the temperature measurement module 460 includes one or more TC input amplifiers 462 which condition the temperature measurement signal provided by the thermocouple 464.
• the A/D converter 466 digitizes the temperature measurement after which it is scaled by the micro controller 468 that in turn communicates the temperature value to the main controller 430 across a galvanic isolation barrier, which may be the same as or different from galvanic isolation barrier 440, via a communications bus, which may be the same or different from communications bus 450.
• a second linear input 470 is provided to facilitate cases where a linear input such as 0-5 vdc can be provided that indicates the resistive element temperature, such as a signal from an optical pyrometer or other similar source.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Measurement Of Resistance Or Impedance (AREA)
• Measurement Of Current Or Voltage (AREA)
• Measuring Temperature Or Quantity Of Heat (AREA)

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• 2006
  • 2006-06-19 US US11/454,922 patent/US7825672B2/en active Active
• 2007
  • 2007-06-04 CN CN2007800271251A patent/CN101490573B/zh active Active
  • 2007-06-04 EP EP07795688.6A patent/EP2038667B1/en active Active
  • 2007-06-04 JP JP2009516498A patent/JP5209617B2/ja active Active
  • 2007-06-04 WO PCT/US2007/013093 patent/WO2007149205A2/en not_active Ceased
  • 2007-06-04 KR KR1020097000785A patent/KR101359232B1/ko active Active

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