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Browse Prior Art Database

Measurement of Motor Time Constant

IP.com Disclosure Number: IPCOM000075795D
Original Publication Date: 1971-Nov-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Lohmeier, WL: AUTHOR

Abstract

This circuit measures the time constant t(c) of a motor, by monitoring the current waveform generated by the motor during a start operation. The current is sensed by monitoring the voltage across the low-resistance shunt 10 in series with the motor. The time constant t(c) is defined as the time for the motor currant to reach 63 % of the peak current, minus the run current after the motor is energized. These currents can be detected by monitoring the shunt 10.

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Measurement of Motor Time Constant

This circuit measures the time constant t(c) of a motor, by monitoring the current waveform generated by the motor during a start operation. The current is sensed by monitoring the voltage across the low-resistance shunt 10 in series with the motor. The time constant t(c) is defined as the time for the motor currant to reach 63 % of the peak current, minus the run current after the motor is energized. These currents can be detected by monitoring the shunt 10.

In operation, timing circuits 12 activate relay 14 to pass a drive voltage from the power supply 16 to the motor 18. Effectively of voltage is applied to the motor. The current through the motor will rise to a peak and exponentially decay to the run-current value.

The motor current waveform is detected by monitoring the voltage across shunt resistor 10. This voltage is amplified by the operational amplifier 20 and passed to the peak detect-and-hold 22 and the sample-and-hold 24.

The sample time of the sample-and-hold 24 is controlled by the timing circuits
12. When the motor has been operating long enough to reach the run-current value, timing circuits 12 trigger the sample-and-hold 24 to sample the amplified voltage from across the shunt 10.

The peak detect-and-hold 22 monitors the amplified voltage from shunt 10 and stores the value of the peak voltage V(p). With the peak voltage stored at circuit 22, and the run current voltage V(r) stored at sample-and-hold 24, the resi...