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Coil Overheating Protection Circuit

IP.com Disclosure Number: IPCOM000060299D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Gareri, A: AUTHOR [+2]

Abstract

Using the coil itself as a sensor to sense its own temperature, by monitoring the change of resistance as a function of temperature, permits the convenient detection of coil overheating in print actuators. The inductance of the coil is compensated by a delay, and a comparator provides the standard for determining the overheat condition. Coil overheating, due to the high usage of a print actuator at high speed, degrades printing quality and may damage the coil. A coil temperature-detecting device senses the temperature of the coil and gives a warning to the control unit to take action, either to slow down or to stop the printing for a period of time.

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Coil Overheating Protection Circuit

Using the coil itself as a sensor to sense its own temperature, by monitoring the change of resistance as a function of temperature, permits the convenient detection of coil overheating in print actuators. The inductance of the coil is compensated by a delay, and a comparator provides the standard for determining the overheat condition. Coil overheating, due to the high usage of a print actuator at high speed, degrades printing quality and may damage the coil. A coil temperature-detecting device senses the temperature of the coil and gives a warning to the control unit to take action, either to slow down or to stop the printing for a period of time. This circuit shown in the figure senses the temperature of the coil and provides a pulse signal to indicate that the coil has reached a predescribed temperature, using the coil itself as a sensor, based on the resistance increase of copper wire which is .39% per degree C. The typical resistance of a wire matrix coil is in the 20-ohm range, and the resistance of a line printer actuator coil is in the 5-ohm range. The comparator 1 gives a low signal if the temperature exceeds the predescribed limit. Delay 2 compensates for the current rise time due to the inductance of the coil, and provides a reliable signal to the control unit to detect the coil overheating. In the circuit, the Rext at resistance 3 is computed based on the current across the coil 4 at the coil- limiting temperature,...