Apparatus for measuring the degradation of a sensor time constant

摘要

Methods and apparatus for on-line detection and measurement of degradation or undesirable changes in the time constants of sensors used in monitoring a system are disclosed. Methods and apparatus of this invention are particularly suitable for use in complex and high-risk industrial processes or other operations where it is undesirable and expensive or dangerous to allow certain parameters of the operation to change above or beyond a predetermined amount. This invention includes a detector for determining when a signal from a sensor crosses a preselected signal level such as for example a zero level. The output of the detector or zero crossing detector is provided to a counter or other means which determines the rate of the zero crossing by counting the number of crossings per a specific time period provided by a timer. The determined rate of the zero crossing is then compared to a preselected acceptable rate to determine whether or not the sensor time constant has increased beyond the preselected allowable value. If the detected crossing rate is less than the acceptable value, (corresponding to a time constant above its acceptable value) an alarm will be sounded to alert the operator of the system of the degraded sensor response time.