Reset, automatic manual

Otirrent Volta nc Cycles Reset Automatic Manual ... 

There are many kinds of thermal switches. Some are normally open some closed. Different switches have different preset action temperatures. Some operate one time, whereas others reset automatically after the temperature returns to a preset value. Others have a manual reset button. 

Preparation for use, including setting and adjustment Startup Communicate Automatic Manual Semiautomatic Steady state of operation Resetting Shutdown Maintenance... 

Reset A manual or automatic operation that restores a mechanism or device to its prescribed state. 

Since excess pressure indicates malfunction of part of the system - usually a condenser fault or incorrect closure of a valve - the high-pressure switch should be reset manually, not automatically. 

Some machines by nature generate transients that can affect machine operation if they contain sensitive circuits. Figure 3.25 shows a waveform produced by a foodprocessing machine. The transients occurred several times each day as the machine automatically turned on and off. Severe transients caused the machine to go into a lockout mode which required the operator to manually reset the machine. The problem was fixed by providing a dedicated circuit of low impedance for the machine. This reduced the transient to levels that could be lived with. 

Tuning. Typical values are K.. = O. IK, Tj = 0.75 (0 + x), and = 0.0. The proportional band (lOO/A" ) and the reset time (1/T,) can be calculated from these. When fine tuning, observe the behavior of both the controlled and manipulated variables. Always use an implementation that includes antireset windup protection for use when the manipulated variable encounters a constraint. Use an implementation that includes initialization that starts automatic control bumplessly from the last manual condition. The digital execution period should be fast with respect to the feedback dynamics, with At < 0.05 (0 -i- x) where possible. 

This subclause addresses the potential hazard that may be created if a SIS automatically restarts the process immediately after the trip condition is corrected. Each SIF should be analysed to determine how it should be reset once the trip condition is corrected. Normally restarting should only be possible after a manual action of the operator. 

The nuclear system protection system initiates the rapid insertion of the control rods to shut down the reactor. The system is of the fail-safe design where it will trip on loss of electrical power but will not trip and cause a scram on the loss of a single power source. The four trip channels are physically separated from each other and from other equipment precluding the possibility of interactions that could cause possible false scrams or failure to scram. The logic requires a manual reset by the operator, which is automatically inhibited for 10 s. One reset switch is used for each trip channel. Failure of a single trip channel, division logic, or a system component will not prevent the normal protective action of the nuclear system protection system. 

This resetting can be done manually or automatically. With manual reset, a potentiometer is used to electrically shift the proportional band. The amount of shifting has to be done in small increments until the controller power output matches the process power demand as setpoint temperature. 

Provide for manual override and reset capability for automatic control fimctions utilized within the system ... 

Nuclear power plants include engineered safety features (ESF) that initiate automatically to perform required safety functions. These safety systems allow also for operator intervention and control during operating events. Once the operator intervenes and takes manual control, many ESFs will not automatically re-initiate until the ESF is restored to a standby configuration with the actuation logic reset or rearmed. 

The reactor protection system shall be designed in such a way that necessary automatic actions, once initiated, cannot be impeded or prevented by manual actions and that no manual actions are necessary within a short period of time following an accident. Protective actions, once initiated automatically by the reactor protection system, shall be designed to proceed to completion. Such automatic actions by the reactor protection system shall not be self-resetting and a return to operation shall require dehberate operator action. 

The priority of automatic actions over manual operator actions was ensured in the original design. In the course of development of the new symptom based EOPs some operator actions were identified as significant. An example is the reduction of safety injection flow the operator cannot take this action in the wide range of pressure below 8.3 MPa and temperature above 180°C. The safety signal reset capability is to be implemented when justified. 

The operation of the robot from the outside of the fence by unauthorised manual operation is assumed to have to be deliberate This would require the keyswitch to be reset to the auto position and the programming terminal to be used before a program could be executed in the automatic mode ... 

Manual—automatic switching is not necessary since both controllers have anti reset-windup. 

Anti reset-windup for loops with overrides (also simplifying manual-automatic switching)... 

A true cascade system (see Figure 12.3) has at least two controllers a primary or master one and a sectMidary or slave one, whose set point is normally set by the primary controller. An example would be column-top temperature control cascaded to reflux flow control. C5ur preferred scheme uses the secondary variable for external reset feedback to the primary ccxitroller. This gieady minimizes the need for manual—automatic switching—none is needed in the primary control station. 

Controls (all on the front panel) meter calibrated 0-60 and 0-600itA potentiometer for current selection manually reset timer with automatic cut-off... 

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