Manual hardware separation

The human factors audit was part of a hazard analysis which was used to recommend the degree of automation required in blowdown situations. The results of the human factors audit were mainly in terms of major errors which could affect blowdown success likelihood, and causal factors such as procedures, training, control room design, team communications, and aspects of hardware equipment. The major emphasis of the study was on improving the human interaction with the blowdown system, whether manual or automatic. Two specific platform scenarios were investigated. One was a significant gas release in the molecular sieve module (MSM) on a relatively new platform, and the other a release in the separator module (SM) on an older generation platform. 

The key to effective troubleshooting is expressed in the old adage, divide and conquer. It is important to locate the portion of the control loop hardware that is causing the poor performance the hnal control element, the sensor system, the controller, or the process. The place to start is to test each system separately to determine whether that portion of the control loop is operating properly. The hnal control element can be evalnated by applying a series of input step tests. That is, the input to the hnal control element, which is normally set by the controller, can be manually adjusted. The test allows the determination of the dynamic response and deadband of the actuator system. If the performance in these two areas is satisfactory, there is no need to evaluate the actuator system further. 

The control computer/DCS system consists of controllers, A/D and D/A converters, and the signal conditioifing hardware and software, i.e., filtering and validation. Each of these components requires separate evaluation. Table 15.5 lists possible problems with the controller/DCS system. One way to initially check controller tuning is to place the control loop in manual (open the control loop) and observe whether the controlled variable lines out to a steady-state or near steady-state value. Comparing the open-loop and closed-loop performance indicates whether the controller is upsetting the process. If not, disturbances to the control loop in question are the primary source of the upsets. 

An outline of the process is shown in Fig. 1. Our discussion will include a general description of the hardware to generate the MS raw data (the introduction of the sample at atmospheric pressure into the mass spectrometer, which is under vacuum), the formation of the mass fragments and their separation from one another, focusing, and detection. The raw data thus obtained require some form of evaluation to become intelligible, a process that calls for automatic and/or manual computer work. A few examples of real-life forensic studies will help explain common approaches used in such a pursuit. 

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