| 摘要 |
<p>In a surface reflectance meter (Fig. 2) for directing light to a surface (201, 202, 203) receiving light reflected from the surface (209, 210) and measuring the rate of change of light flux upon withdrawal of a light chopper (204) from the optical path (103), a fault detection means (Figs. 9, 10) which detects and indicates a fault in the flux rate of change measurement. In the preferred embodiment the rate of change of flux is detected by measuring the time (630) for the light intensity to increase from a first predetermined intensity (610) to a second predetermined intensity (620) and the fault detector means (Figs. 9 or 10) detects and indicates a fault when the light intensity does not reach the second predetermined intensity (620) within a predetermined period of time (630). The surface reflectance meter is reset for repetition of the measurement upon indication of a fault. This invention is useful in portable surface reflectance meters which must be hand held to the surface to be measured, because instability in holding the meter to the surface can cause the fault.</p> |
