Abstract: A frequency error correction device for an OFDM receiver is proposed. The receiver receives an OFDM signal with a preamble section and a payload section including pilot carriers. The frequency error correction device includes a first frequency correction unit for correcting a relative phase error in a predetermined period of time based upon a frequency error in the preamble section of the OFDM signal in time domain, and a second frequency correction unit for correcting a remaining phase error in every predetermined period of time based upon the pilot carriers of the OFDM signal in frequency domain.

Abstract: A frequency error correction device for an OFDM receiver is proposed. The receiver receives an OFDM signal with a preamble section and a payload section including pilot carriers. The frequency error correction device includes a first frequency correction unit for correcting a relative phase error in a predetermined period of time based upon a frequency error in the preamble section of the OFDM signal in time domain, and a second frequency correction unit for correcting a remaining phase error in every predetermined period of time based upon the pilot carriers of the OFDM signal in frequency domain.

Abstract: A welding current measuring apparatus for a resistance welding machine comprises a current detector for use in measuring and detecting welding current flowing through the resistance welding machine, a memory for successively storing and holding the current values detected over the whole energizing time, and a device for specifying a desired energizing cycle interval to compute and display current values after completion of welding, wherein any energizing cycle interval is specified at will after completion of welding so that the current values or the current waveform in the specified interval can be displayed.

Abstract: A secondary conductor supervising device of a resistance welder control system for supervising short-circuit, disconnection, and/or deterioration of a secondary conductor by means of a current flowing through a resistance welder, which comprises a voltage detecting circuit for detecting a voltage from the secondary conductor, inclusive of a secondary cable, of the resistance welder, a current detecting circuit for detecting a current flowing through the resistance welder, a divider for dividing the output of the voltage detecting circuit by the output of the current detecting circuit, an average computer for averaging the output of the divider over a part or the whole of a welding period, a supervisory level setting unit for setting a resistance value such as of the secondary conductor, and a comparator for comparing the output of the setting unit with the output of the average computer based on the welding period.

Abstract: A spot welding control method is disclosed wherein the welding current and welding time are controlled, in response to changes in the shape of the point of the electrode tip. At each weld point, the lowest value of the varying resistance between the electrode tips is detected in an initial welding period, and each detected lowest value is successively held and stored. At each weld point, a running average of the lowest resistance values is computed, bases on the resistance date of a group of weld points composed of the weld point just completed through a number of preceding weld points, the number of which is preset. The weld conditions are changed from one set of predetermined parameters to another when the computed average reaches the then prevailing threshold limit, following which the threshold is reset. The thresholds are preset depending upon the degree of wear of the electrode tip, whereby welding is continued under newly-selected weld conditions corresponding to the present threshold.

Abstract: A control method of resistance welding for controlling weld conditions, such as welding current and welding time, in response to a change in material of weldments, which comprises the steps of detecting the local lowest value of resistance between electrode tips appearing in an initial welding period, comparing the detected lowest value with a plurality of reference resistance values preset correspondingly to materials of weldments of different sorts and divided into plural classes to determine the material of a weldment under process, and changing the weld conditions, such as welding current and welding time, depending upon the determined material.

Abstract: A method of controlling constant-current for resistance welding machines comprising the steps of: detecting the welding current flowing into the primary coil or the secondary coil of a welding transformer, applying a first half-wave current having a predetermined first phase control angle, detecting the current value and the current conduction angle at that time, calculating a power factor angle of the resistance welding machine from the detected conduction angle and the phase control angle, calculating a second phase control angle, by which a current value corresponding to a previously set value of the next half-wave of current is obtained, from the calculated power factor angle, the detected conduction angle and the detected of current value, applying the next half-wave current at the second phase control angle through a thyristor circuit to a work to be welded, and repeating the above control operation during an entire welding cycle.