Abstract: A circuit and method for measuring resistance in an active and high temperature environment is provided using a low frequency square wave as an input. The square wave input is fed through the unit under test into a full-wave rectifier and RMS circuit. The full-wave rectifier and averaging circuit cancel out errors caused by the Seebeck effect and noise. The resulting d.c. signal is proportional to the resistance of the unit under test and can be displayed.

Abstract: A soldering system includes M soldering tools, where M is .gtoreq.1 and is an integer and N soldering tips where N is .gtoreq.1 and is an integer with one of the N tips attached to one of the M soldering tools. The soldering system also includes a control circuit connected to the one tool having the one tip attached to it. The control circuit maintains the one tip at a desired temperature. The control circuit has a device for inputting the desired temperature at which the control circuit maintains the temperature of the one tip. In a preferred embodiment, each of the N tips have an identity and each of the M tools have an identity. The control circuit maintains the one tip attached to the one tool at a desired temperature which is inputted into the control circuit through the input device. The control circuit identifies which of the N tips is attached to the tool by the identity of the one tip attached to the one tool being inputted into the control circuit through the input.

Abstract: A temperature probe using a first thermocouple junction at the end of a metal tip for measuring the temperature of an object is also provided with a second thermocouple junction on the metal tip at a predetermined distance from the first thermocouple for detecting heat flow in the tip from the first thermocouple toward the second thermocouple. Electronics responsive to both themocouples drive a heater which maintains the second thermocouple at substantially the same temperature as the first thermocouple, thereby to eliminate heat loading by the probe on the object being measured. A single adjustable resistance temperature detector electronically connected in series with the metal tip is used to calibrate the probe and compensate for errors in the temperature readings of the first and second thermocouples. The resistance temperature detector is made up of a wire located in the handle of the probe and is adjusted by stretching the wire to reduce its diameter and bulk resistance.