Apparatus and method for sensing failed temperature responsive sensors

US5834943A · kind A · utility

Inventor

• Mark E. Miller · Versailles, US

Key dates

• Filing date: Nov 25, 1996
• Grant date: Nov 10, 1998
• Expiry date: Nov 25, 2016

Classification

• Technology area (CPC G): Physics
• CPC primary: G08B29/14
• WIPO field: Control
• WIPO sector: Instruments

Abstract

A microprocessor control (10, 24) has one or more temperature responsive thermistor sensors (20, 26, 28) used to provide temperature inputs to control operation of a temperature control system. The microprocessor control subjects the thermistor sensors to a series of diagnostic tests prior to reading the thermistor sensors, the tests including short and open circuits, shorts to ground or power and leakage paths to ground. The thermistors, along with a reference resistor (R11, R26) form an RC charge circuit with a capacitor (C6, C6'). The capacitor is charged through each thermistor and reference resistor for selected open and short tests while a watch dog timer is used to determine the time taken to charge the capacitor via a timer capture port coupled to the capacitor. The temperature control system has a power supply having a logic ground and a chassis ground of different potentials which are utilized in the leakage test by turning off the power source to the thermistors and setting a watch dog period to determine if leakage through a respective thermistor to chassis ground has caused the capacitor (C6, C6') to charge sufficiently to cause a timer capture.