In-situ Resistometry for Heat Treatment Monitoring and Control

Measurement technique

The sample to be measured is sealed inside a quartz tube being continuously evacuated by a vacuum pump, to avoid sample oxidation. This quartz tube is supported inside the alumina tube of a furnace, which is heated under the control of a Eurotherm temperature control (itself optionally under computer control).

To detect small changes of resistance, we use an alternating current (AC) four-wire method with a lock-in amplifier. An AC current source is set to provide a stable 30 mA current at a frequency of around 63 Hz (to avoid mains noise whilst still avoiding problems with the skin effect), and to provide a suitable reference signal to the lock-in amplifier. Band-pass filtering is applied to the measured signal, and the resulting voltage is recorded by the computer. The temperature measured by a thermocouple near the sample is also logged.

The schematic below illustrates the entire equipment set-up. Hover your mouse pointer over a section of the equipment for more detailed information about it. Click on the quartz tube, or follow this link, to view an enlargement of the sample connections.

Schematic illustration of the equipment used for in situ resistance measurements during heat treatment.