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# Solenoid Current Dip Timing Circuit

IP.com Disclosure Number: IPCOM000060418D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 31K

IBM

## Related People

Bierschbach, JE: AUTHOR [+3]

## Abstract

Performance of a solenoid and its associated hardware is determined by monitoring the solenoid's current vs. time waveform. The purpose of the circuit is to convert the solenoid's DC current vs. time waveform into a pulsed digital signal which can be analyzed by a microcomputer. Prior to energizing solenoid L1, capacitor C1 is charged to +5V through R2. The voltage on the positive input to IC 1 is ground. The voltage on the negative input to IC 1 is -.050 V, as determined by R4 and R5. The voltage at point "B" is +5 V. When L1 is energized, by turning on T1, C1 is clamped to .9 V. This forces the positive input of IC 1 to -.7 V due to the clamping effect of D2 which provides fast recovery. The voltage at point "B" goes to ground. C1 now discharges toward ground through R3.

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Solenoid Current Dip Timing Circuit

Performance of a solenoid and its associated hardware is determined by monitoring the solenoid's current vs. time waveform. The purpose of the circuit is to convert the solenoid's DC current vs. time waveform into a pulsed digital signal which can be analyzed by a microcomputer. Prior to energizing solenoid L1, capacitor C1 is charged to +5V through R2. The voltage on the positive input to IC 1 is ground. The voltage on the negative input to IC 1 is -.050 V, as determined by R4 and R5. The voltage at point "B" is +5 V. When L1 is energized, by turning on T1, C1 is clamped to .9 V. This forces the positive input of IC 1 to -.7 V due to the clamping effect of D2 which provides fast recovery. The voltage at point "B" goes to ground. C1 now discharges toward ground through R3. When the positive input of IC 1 becomes greater than -.050 V point "B" switches to +5V. Current through the coil increases until the solenoid plunger seats. Seating of the plunger increases the back-EMF of the coil and causes the current to "dip", as at point 10. The "dip" in waveform "A" causes waveform "B" to pulse again. Resistor R1 is used to convert coil current into a voltage waveform, point "A". Point "B" is connected to a negative edge sensitive process interrupt point of a microcomputer which measures the current dip timing. Only one circuit is required for any number of solenoids, as long as only one solenoid is activated at a time. The circuit will...