This paper presents results of work aimed at characterising the zero offset stability in novel thick film strain gauges. Some theories are presented to explain the apparent lack of repeatability exhibited by thick film strain gauges when they are subjected to cycling of load or temperature. The devices studied are z-axis (k{sub}33) load sensors fabricated on insulated stainless steel substrates and include examples of novel commercially developed force sensors. Devices loaded with compressive strains using a purpose designed test jig were found to exhibit a significant zero offset shift, which is negative up to a certain level (typically 1000 micro strains) and then increasingly positive when strained beyond this point. Repeated cycles of loading then produced a certain level of stability until the previous maximum value of applied strain was exceeded. The gauge factors of the devices exhibited a strong inverse dependence on applied strain and apparent super high gauge factors of up to 250 or more were obtained at low levels of strain. Temperature coefficient of resistance (TCR) measurements showed the devices to exhibit characteristics that depend significantly on the device geometry. The TCR was found to increase positively with increasing device thickness and surface area. The effect of overglazing the devices was found to decrease the TCR. In general the TCR of thick film resistors on stainless steel substrates exhibit positive TCRs at room temperature. However, it was noted that if a device was thin, had a sufficiently small surface area and was overglazed, then the TCR could exhibit a negative value at room temperature.
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