Safety instrument systems typically incorporate emergency shutdown valves which are normally in a fully opened or a fully closed state and are controlled by a logic solver, a Programmable Logic Controller (PLC), or an emergency shutdown controller of some type to change states in the event of an emergency situation. To ensure that these valves can function properly, process control system operators typically periodically test the emergency shutdown valves by running these valves through a stroke test, which partially or completely opens or closes the valve. Because these tests are typically performed while the process is operating on-line or is operational, it is important to perform any test reliably and then return the valve to its normal state as quickly as possible. In this context, the term “normal state” refers to the position or state of the emergency shutdown valve when there is no emergency and the emergency shutdown valve is not being tested, i.e., when the process is operating normally.
In many cases, the emergency shutdown tests are performed at predetermined intervals by remotely located controllers. For example, emergency shutdown tests may be performed only a few times each year due to cumbersome test procedures and issues related to manpower. Also, during emergency shutdown tests, the emergency shutdown valve, or other emergency shutdown device being tested, is not available for use if an actual emergency event were to arise. However, limited, periodic testing is not an efficient way of verifying the operability of an emergency shutdown test system. As a result, digital valve controllers have been, in some cases, programmed to assist in the operation of the valve test to make the testing more automatic, user friendly and reliable.
Additionally, it is typically important that any emergency shutdown system be able to activate an emergency shutdown device (an emergency shutdown valve, for example) to its safe condition even when commanded by the emergency shutdown controller to do so in the unlikely but possible situation where an emergency event occurs during an emergency shutdown device test. In this context, the term “safe condition” refers to the position of the emergency shutdown device that makes the process plant or portion of the process plant “safe.” Typically, this safe position is associated with a position of the shutdown device that shuts down or halts some portion of the process plant.
While there are many systems that test the ultimate emergency shutdown device, such as an emergency shutdown valve, itself, in many cases there is supporting equipment associated with the emergency shutdown device that should also be tested to assure the complete operability of the emergency shutdown capabilities at any particular plant location. For example, in some pneumatic valve configurations, a solenoid valve is connected between a pneumatic valve actuator of an emergency shutdown valve and an emergency shutdown controller to redundantly control the operation of the valve actuator in response to signals from the emergency shutdown controller. While the emergency shutdown valve may be functional, it is possible for the solenoid device to become defective and therefore not operate properly as a redundant method of actuating the emergency shutdown valve. In some cases, an improperly operating solenoid device may even prevent the emergency shutdown valve from actuating properly when the emergency shutdown controller sends a shut-down signal to the valve controller for the emergency shutdown valve.
While it is possible to develop and provide specialized equipment at each emergency shutdown location within a plant to perform testing of each different emergency shutdown device and its supporting equipment, it is more desirable to provide a universal or generic set of equipment that may be used in many different situations to test different types of emergency shutdown devices and the supporting equipment associated therewith or to perform other functions in the plant. For example, it is desirable if such versatile equipment is able to control and test different types of emergency shutdown valves and solenoid valve configurations while simultaneously or alternatively operating as part of a closed loop distributed process control system.