Autographic determination of thermally-induced linear changes in ceramic bodies

The determination of changes in length of ceramic compositions as a function of temperature is frequently required in ceramic research and testing. With the use of an observer, excellent means are available for determination of changes in length over moderate ranges of temperature. However, the extended period required for some tests makes desirable the automatic recording of length change as a function of temperature. There has been in use in the Ceramic Engineering Department a furnace arranged for determination of length changes; this furnace, shown in Figure 1, is so arranged that change in sample length causes linear displacement of a refractory rod in contact with the test piece. The temperature of this furnace is determined in the usual way by use of either a thermocouple or a radiation pyrometer. For the purpose of recording changes in one variable as a function of another, there is available a Leeds and Northrup X-Y Recorder. This instrument consists of two self-balancing potentiometers so connected that change in one measured voltage moves a recording pen in a horizontal direction, while the other produces a vertical motion of the recording chart, thus recording one voltage as a function of the other. The problem of this work has been to design and construct a device to permit the use of the X-Y Recorder for obtaining, automatically, a plot of change in length as a function of temperature, using the existing furnace and a standard thermocouple or radiation pyrometer for temperature-voltage conversion --Introduction, page 1