Abstract: A field device comprising a signal processing unit that generates a digital measurement, control or regulation signal, and comprises an output stage that converts the digital measurement, control or regulation signal into an analog voltage or current signal, The field device also includes a monitoring device which comprises a measuring device that detects the analog voltage or current signal and converts this signal into a digital voltage or current measurement signal, a first digital low-pass filter for filtering the digital measurement, control or regulation signal, a second digital low-pass filter having the same cut-off frequency as that of the first digital low-pass filter, a comparator downstream of the low-pass filters, and an evaluation device that generates an error message when the deviation between the compared signals exceeds a pre-determined level.

Abstract: A method for checking plausibility of digital measurement signals, wherein the method comprises forming a trend function for a prescribed number of successive measurement values of the measurement signal, determining the differential values between the measurement values and the trend function if the leading digit of at least one differential value is equal to zero, multiplying all differential values by a factor so that the leading digits of all differential values are non-zero values, determining a deviation between the frequency distribution of the leading digits of the differential values and the frequency distribution in accordance with Benford's law, and generating a warning message if the deviation exceeds a threshold value.

Abstract: A field device comprising a signal processing unit that generates a digital measurement, control or regulation signal, and comprises an output stage that converts the digital measurement, control or regulation signal into an analog voltage or current signal, The field device also includes a monitoring device which comprises a measuring device that detects the analog voltage or current signal and converts this signal into a digital voltage or current measurement signal, a first digital low-pass filter for filtering the digital measurement, control or regulation signal, a second digital low-pass filter having the same cut-off frequency as that of the first digital low-pass filter, a comparator downstream of the low-pass filters, and an evaluation device that generates an error message when the deviation between the compared signals exceeds a pre-determined level.