Abstract: A diagnostic test unit for deterministically measuring one or more parameters, such as dead band, dead time, response time, gain, or overshoot, of a process control device that is connected in a process control loop during operation of a process includes a switch controller, a signal generator, a switch, a response accumulator mechanism, and an analyzer mechanism. The switch controller monitors a process signal during operation of the process to determine whether the process signal is substantially stable. In the event that the process signal is substantially stable, the switch replaces a control signal with a diagnostic test signal generated by the signal generator. The response accumulator is in communication with the process control loop to obtain an indication of the response of the process control device to the diagnostic test signal. The analyzer unit then determines the device parameter from the test signal and the response indication.

Abstract: An apparatus for nonobtrusively determining one or more parameters, such as dead band, dead time, or response time of a process control device that is connected on-line in a process control loop includes a measurement unit and a processing unit. The measurement unit is coupled to the process control loop to detect stochastic changes in a control signal sent to the process control device and to detect an indication of the response of the process control device to the changes in the control signal while the process control device is operating on-line. The processing unit calculates the device parameters from one or more sets of the detected changes in the control signal and the detected response indication.

Abstract: Disclosed herein are valve seals wherein an annular metallic seal member is retained in an annular recess in a valve body wall, the seal member being resiliently deformable in both axial and radial directions. A resilient annular Belleville spring portion is provided linking an inner sealing portion and an outer flange portion which is sealingly engaged by the valve body. When a valve employing this seal arrangement is closed, differential pressure acting from either direction urges a valve closure member and the seal member in a downstream direction, and forces the seal member and the valve closure member into tighter sealing engagement.