A method of measuring a desired frequency by comparing it with a standard frequency. The zero crossings of both frequencies are detected. A command pulse is generated at each coincidence and is used to start and stop a pair of frequency counters adapted to count the desired and standard frequencies. A measure of the desired frequency is obtained by multiplying the known standard frequency by the ratio between the desired count and the standard count obtained in the two frequency counters.
Signal comparison arrangement for comparing a first and a second analog signal with each other. For each of these signals the number of zero-crossings occurring within each measuring interval of a sequence of N consecutive measuring intervals T(1), T(2), . . . T(N) is counted. The N numbers x(1), x(2), . . . x(N) which represent the numbers of zero-crossings of the first analog signal in the consecutive measuring intervals T(1), T(2), . . . T(N) and the N numbers y(1), y(2), . . . y(N) which represent these numbers of zero-crossings of the second analog signal in the said measuring intervals, are applied to a programmable computer which determines the value of a statistical quantity by means of these 2N numbers and compares this value with a threshold value. This statistical quantity may be formed by the directional coefficient of a straight line which is closest to either the N numbers x(n), or the N numbers y(n), but may alternatively be formed by the correlation coefficient.
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.
A frequency discriminator circuit is provided having increased resolution for detecting the frequency of a data input signal above and below a predetermined frequency threshold by monitoring a count value. The output signal of the frequency discriminator circuit remains at a first logic state provided the count value is reset by the data input signal before reaching a predetermined count value signifying that the frequency of data input signal is above the predetermined frequency threshold. The output signal of the frequency discriminator circuit switches to a second logic state if the count value reaches the predetermined count value before receiving a reset signal thereby indicating that the frequency of data input signal is below the predetermined frequency threshold.
A frequency of a signal, particularly a frequency, partly varied as time passes, of a signal is counted in real time by producing a delay signal by delaying the signal as much as a predetermined time, detecting delayed zero-cross pulses from the delayed signal, detecting zero-cross pulses from the non-delayed signal, counting a first number of the delayed zero-cross pulses after the predetermined time is over, counting a second number of the zero-cross pulses during and after the predetermined time, producing a number difference between the first number and the second number by subtracting the first number from the second number and halving the number difference. The predetermined time is designated longer than a half period of the signal frequency to be counted. When the predetermined time is set long, the average frequency of the signal is counted, and when that is set short comparing with the partly varied interval of the signal frequency, the partly varied frequency of the signal is counted in real time.
An arrangement for coarse and vernier measuring of the delay or phase shift introduced by a delay path by generating a recurrent pseudorandom signal at an original chip clock rate derived from a reference clock. At the receiving end of the delay path, a delay locked loop regenerates the chip clock and the pseudorandom signal at a phase established by the delay. The coarse count is measured by the number of chip clock cycles. The vernier delay is measured in terms of a fractional portion of a chip clock cycle. The vernier measurement is made by starting a counter which counts reference clock signals in response to a coincidence of the original chip clock and the reference clock, and by ending counting and latching the count in response to coincidence of the regenerated chip clock and the reference clock.
