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Automating Surge Current Measurement

IP.com Disclosure Number: IPCOM000060831D
Original Publication Date: 1986-May-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Schirmer, EC: AUTHOR

Abstract

Measurement of electrical surge currents is automated using unattended synchronization of an oscilloscope external single sweep with an external device, such as a relay, and the programmability feature of the scope. One-shot turn-on waveforms are captured on a repetitive unattended basis and the worst case displayed. The measurement of electrical surge currents is sometimes done in laboratories using a totally attended process which, in short, involves having an operator turning on and off the piece of equipment under testing to be able to capture the current waveform on an oscilloscope. The process has to be repeated many times until the operator is reasonably sure that the highest surge current has been found. In effect, the process is lengthy and inefficient.

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Automating Surge Current Measurement

Measurement of electrical surge currents is automated using unattended synchronization of an oscilloscope external single sweep with an external device, such as a relay, and the programmability feature of the scope. One-shot turn-on waveforms are captured on a repetitive unattended basis and the worst case displayed. The measurement of electrical surge currents is sometimes done in laboratories using a totally attended process which, in short, involves having an operator turning on and off the piece of equipment under testing to be able to capture the current waveform on an oscilloscope. The process has to be repeated many times until the operator is reasonably sure that the highest surge current has been found. In effect, the process is lengthy and inefficient. This process is easily automated by using the hardware and software described herein. The scheme involves interfacing the circuit shown in Fig. 1 to a programmed Tektronix 7854 oscilloscope, for example. The program for the oscilloscope is shown in the flow chart of Fig. 2. The circuit of Fig. 1 has two major functions: (1) turn-on and off the equipment under testing in a continuous fashion, and (2) generate a signal to reset the single sweep of the oscilloscope. Turning on and off is accomplished by using an AC relay driven by a 555 timer, and resetting of the single sweep is obtained from the collector of transistor Q5 which is a switch to ground. The duty cycle of the relay can be adjusted by changing resistors R4 and R5. R4 controls the time that the relay is closed, and R5 controls the time the relay is open. An approximation formula is Time = .67 x R x C5. Safety of the whole design is enhanced by using the light-emitting diodes (LEDs) to indicate the status of the AC relay. The program shown in Fig. 2 inspects the current waveform acquired on single sweep mode and makes logical decisions based on the peak value of the absolute value of the waveform. The program takes as input the number of times that the user wants the surge current test to be performed. Then, the program waits, and when the oscilloscope is triggered, it acquires the first current waveform. Then a loop is executed until the test is performed as many times as the user indicated. While in the loop, the program waits and acquires a current waveform each time the oscilloscope is triggered. Each time a waveform is acquired the program gets the peak value of the absolute value of the curre...