Normalized process dynamics
A sensing system includes a filter construction module that constructs a high pass filter for filtering sensor values indicative of a process variable, the filter construction module setting values for parameters of the filter based on a temperature value indicative of a temperature of the sensor that produced the sensor values.
1. A process field device comprising:
a process variable sensor providing a sensor signal indicative of a process variable;
a temperature sensor providing a temperature sensor signal indicative of a temperature of the process variable sensor;
converter circuitry for converting the sensor signal into sensor values and the temperature sensor signal into temperature values;
a processor implementing a digital filter that filters the sensor values to produce filtered sensor values and executing statistical process monitoring instructions that compute a statistical value from the filtered sensor values, wherein the digital filter is temperature-dependent such that the filter changes as the temperature values change.
2. The process field device of claim 1 wherein the processor constructs the digital filter by applying a temperature value to an equation determined by fitting a curve to parameter values determined for filters constructed for a plurality of temperature values.
3. The process field device of claim 2 wherein the filters constructed for a plurality of temperature values are each constructed to produce a target frequency response.
4. The process field device of claim 3 wherein the target frequency response comprises a frequency response of a standard deviation of filtered sensor values.
5. The process field device of claim 3 wherein the target frequency response comprises a frequency response associated with a model sensor operating in a different range from the sensor and at a selected temperature.
6. The process field device of claim 3 wherein the target frequency response comprises a frequency response of a model sensor with a constant frequency response at all temperatures.
7. A control system comprising:
a filter that filters a series of sensor values to produce filtered values; and
a statistical process monitoring unit that determines a statistical value from the filtered values and that issues an alert when the statistical value crosses a threshold, wherein the filter filters the sensor values to achieve a desired frequency response in the statistical value that matches a frequency response in the statistical value produced from sensor values generated by a sensor operating in a selected range.
8. The control system of claim 7 wherein the filter comprises a temperature-dependent filter that is constructed by applying the temperature value to respective equations that each define a separate parameter of the filter.
9. The control system of claim 8 wherein each equation is constructed by fitting a curve to values of a filter parameter determined at different temperatures.
10. The control system of claim 7 wherein the desired frequency response of the statistical value further matches a frequency response in the statistical value produced from sensor values generated by the sensor operating at a selected temperature.
11. The control system of claim 7 wherein the desired frequency response of the statistical value comprises a frequency response produced at least in part by a sensor operating in a different range from a sensor that produced the series of sensor values.
12. The control system of claim 7 wherein the desired frequency response of the statistical value comprises a frequency response produced at least in part by a sensor that was manufactured differently from a sensor that produced the series of sensor values.