Discussion on GDS independence
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When implementing interlocks for flammable and toxic substances (other than fire-related interlocks), can the alarm digital signal from the gauge head be sent directly to the DCS for use in these interlocks, or should the GDS output DO signals to the DCS? However, it has been suggested that the combustible and toxic gas alarm system should be independent. In my opinion, GDS is primarily used for centralized display of alarms; it is not intended for use in interlocking functions. If GDS were to output DO signals to directly control devices such as dampers, it would be quite complicated, as electrical circuits would need to be modified. Moreover, since fan and valve controls are usually handled via the DCS system, this would add even more complexity. By independence, does it mean that the system should be separate from other systems, or does it also mean that the signals from the combustible and toxic gas detectors must be independent and can only be connected to GDS?
Please refer to the **standard specification GB/T 50493-2019 Design Standards for Detection and Alarm of Flammable and Toxic Gases in Petrochemical Industries**. The independence of the GDS system means that the flammable and toxic gas monitoring and alarm systems are installed separately; detector signals cannot be fed into the DCS/PLC system for alarm purposes. The new version of the standard requires integration with the fire protection system, with the GDS system sending DO signals to the fire protection/SIS system as triggers for coordinated action.
The combustible and toxic distributed system uses 4-20mA signals to connect to the GDS system; does the gauge also have alarm output points that can be connected to a DCS system for interlocking purposes? The systems are definitely independent of each other. In the new version, interlocking with fire protection equipment requires going through an alarm module first. The combustible and toxic monitoring system is set up independently and connected to the SIS system. What I want to ask is: since this gauge is already connected to the GDS system for alarm functions, are there any other points on this gauge that can be connected to a DCS system for interlocking purposes? Or can the GDS system output DO signals to the DCS system as control signals?
GDS interlock equipment: signals go directly to the equipment, without passing through the DCS. If DCS control is available, modify the electrical equipment schematic by adding remote control points; install solenoid valves on pneumatic valves. Give priority to GDS interlocks, and for electric valves, choose those equipped with SIS/ESD contacts connected to GDS.
Okay, thank you. If the combustible and toxic alarm signals have been transmitted to the GDS via a distributed or bus system, can the digital alarm outputs from the meters be connected directly to the DCS for interlocking purposes, without going through the GDS? Such interlocking should be considered a process safety interlock, not a fire protection interlock
Also, according to the specifications, GDS is primarily used for alarm monitoring and fire linkage; although other control systems use combustible and toxic substances as sensors, it is not clear whether it is appropriate for the GDS system to handle control functions in such cases
GDS signals are generally not used for equipment interlocking in DCS systems; if interlocking is involved with GDS signals, it is likely related to safety aspects, and in such cases they are usually integrated into SIS or FGS systems. At this point, a separate probe should be used; they cannot be shared. If it is indeed necessary to access the DCS for alarms, communication, DO outputs, or a one-to-two signal distributor can be used for transmission.