Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-10-02
2003-08-05
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S060000, C702S189000, C702S107000, C307S002000, C307S007000, C307S130000, C323S247000, C323S357000, C323S371000, C341S155000, C700S075000, C700S286000, C700S297000
Reexamination Certificate
active
06604055
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to cooking devices; specifically, it relates to a system and method for AC line voltage analysis.
2. Description of the Related Art
Variations in the AC line voltage supplied to restaurant food service equipment normally degrade cooking performance. These variations may result in incomplete cooking, overcooking, unappealing appearance, and substandard taste. Thus, this equipment may be equipped with devices that measure AC line voltage to detect such variations.
Referring to
FIGS. 1-3
, schematics of known devices to measure AC line voltage are provided. In
FIG. 1
, device
100
includes resistors
102
and
104
that lower a high line voltage to a low voltage that is safe for input to A/D converter
112
. Bridge rectifier
106
half-wave rectifies the AC waveform. Resistor
108
and capacitor
110
filter the half-wave rectified waveform to a DC voltage. This signal is input to A/D converter
112
, and the digital information is processed by microprocessor
114
.
Although it is a relatively simple device, device
100
has its drawbacks. Specifically, device
100
does not have line isolation, which makes agency approvals, such as those from Underwriter's Laboratories, Inc. (“UL®”), difficult to obtain. In addition, because five distinct components are required, device
100
is costly.
Referring to
FIG. 2
, a second device for measuring AC line voltage is provided. Device
200
includes dedicated step-down transformer
202
that drops a high line voltage to a lower voltage. Bridge rectifier
204
full-wave rectifies the AC waveform. Resistor
206
and capacitor
208
filter the output of bridge rectifier
204
to a constant DC voltage, which is input to A/D converter
210
, and processed by microprocessor
212
.
Device
200
provides the line isolation that device
100
failed to provide. Transformer
202
, however, is very large, heavy, and expensive. Further, the transfer function for transformer
202
is not tightly specified.
Referring to
FIG. 3
, a third known device for measuring AC line voltage is provided. Device
300
includes resistor
302
, which limits the current input to optical isolator
304
. Output
306
is a rectified AC waveform. Resistor
308
and capacitor
310
filter this waveform. Signal conditioning circuit
312
provides gain and offset to present a correct and suitable voltage to A/D converter
314
, the output of which is processed by microprocessor
316
.
Device
300
provides optical isolation from the line voltage. Resistor
302
, however, must be a high-power resistor, which is inherently large and generates heat. Optical isolator
304
has transfer characteristics that are poorly controlled and change over time. Finally, signal conditioning circuit
312
adds an additional part and increases overall manufacturing costs.
SUMMARY OF THE INVENTION
Therefore, a need has arisen for a system and method for AC line voltage analysis that overcomes these and other deficiencies in the related art.
According to one embodiment of the present invention, a system for AC line voltage analysis is disclosed. The system for AC line voltage analysis on an AC line includes a transformer that steps down the AC line voltage, a rectifier that rectifies the stepped down AC line current, a filter that filters the rectified AC line current, a voltage divider that reduces the AC line voltage; and an A/D converter that converts the reduced AC line voltage to digital bits. According to another embodiment of the present invention, a system for AC line voltage analysis on an AC line includes a device that calibrates equipment for measuring AC line voltage analysis, a device that adjusts for at least one load, a device that filters an adjusted measurement, and a device that determines an actual line voltage.
According to another embodiment of the present invention, a method for AC line voltage analysis is disclosed. The method for AC line voltage analysis of an AC line includes the steps of calibrating equipment for measuring AC line voltage analysis, adjusting for at least one load, filtering an adjusted measurement; and determining an actual line voltage.
The method determines the loading effect of loads, such as the heat relay and the pressure solenoid, as well as LED light bars and alphanumeric displays. It may not be necessary to determine the loading effect for all loads.
The net result of the first calibration step is a table of offsets, in A/D bits, which are applied during subsequent AC voltage measurement.
Two known, constant AC line voltages are applied to the transformer, and the process control measures the A/D bit outputs at these two voltages and performs a two-point calibration. The resulting equation is then later used during normal operation to calculate the AC line voltage from the A/D measurement.
After the calibration is performed, the AC line voltage measurement is carried out by the process control. The control software reads the A/D converter.
The control software modifies the A/D reading by the appropriate offsets for load which were one during the A/D measurement.
The control software calculates the AC line voltage from the transfer function found during calibration.
The control software converts the AC line voltage measurement to a percent of nominal line voltage, for the purposes of comparison and indication. This is a user-interface convenience in that the end user need not know the nominal line voltage: if the control reports a line voltage of 100%, the user knows that the line voltage is correct, regardless of the actual nominal line voltage.
REFERENCES:
patent: 4721906 (1988-01-01), Ferguson et al.
patent: 5546331 (1996-08-01), Matthews
Burkett Douglas A.
Landwehr Tim A.
Baker & Botts L.L.P.
Desta Elias
Henny Penny Corporation
Hoff Marc S.
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