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Accurate Digital Thermal Monitoring System

IP.com Disclosure Number: IPCOM000035327D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Baudrion, PY: AUTHOR [+3]

Abstract

This article describes a device for monitoring the temperature of two TCMs by means of a microprocessor interface. The invention provides an accurate monitoring system using no precise voltage reference.

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Accurate Digital Thermal Monitoring System

This article describes a device for monitoring the temperature of two TCMs by means of a microprocessor interface. The invention provides an accurate monitoring system using no precise voltage reference.

With respect to the figure, the invention includes a dividing bridge made of a very accurate resistor R and the thermal resistors Rth1 and Rth2. The voltage of this bridge V1 is transformed with a resistor R1 in current I1: Vref. Rth V1 = ___________ Rth + R Vref. Rth 1 I1 = (__________ ) . ___ Rth + R R1

This current is compared with the output current, I2 of a digital- to-analog converter (DAC) (8 bits, for instance). 8 Ci Vref I2 = K S ____ with K = ______ i=1 2i

R3 where Vref is the voltage reference for the DAC and R3 the resistor which guarantees the maximal output current.

The comparator changes its status when: I1 = I2 Vref Rth 1

Vref 8 Ci (__________) ____ = ______ ( S ____) Rth + R
R1 R3 i=1 2i Rth R1 8 Ci <===> _________ = ____ S
____ Rth + R R3 i=1 2i Rth 8 Ci if R1 = R3 ===> _________ = S ____ Rth + R i=1 2i

Thus, the accuracy of the system depends on the accuracy of the bridge resistor and the accuracy of the DAC conversion; no voltage reference is needed.

When the comparator changes its status, a positive front appears on its output which clocks the status at the input DAC counter into an 8-bit 3-state latch. The status of the latch is refreshed every 256 counter clock pulse cycle.

The code corresponding to...