Problems with flammable and toxic detectors
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This post was last edited by zhoudingshengs on 2024-1-22 at 11:53. Discussion: The skid manufacturers have integrated these flammable and toxic signals into their own PLC systems. The client requires that these toxic and flammable signals be fed into the GDS system in the control room. Is it compliant to have the PLC generate AO signals of 4-20mA?
It is necessary to consider the type of modules in the GDS system; the GDS system used in our project supports 4–20mA signals as well as Modbus communication
Let the PLC output an AO signal of 4-20mA type; GDS receives an AI signal
Hello, 1. As long as your PLC outputs a 4-20mA signal, it is considered a field instrument, and the corresponding AI card of the GDS can receive it. 2. However, you need to consider whether the above solution is feasible. The specification requires that the GDS system be set up independently from other systems, so that in the event of problems with other DCS or PLC systems, the GDS system can still operate and the alarms can still function as intended. Therefore, although your system is independent, your alarm signals are routed through the PLC; once the PLC stops working due to a fault, your alarm signals disappear as well, and thus no protection is provided. 3. If possible, have the alarm signal go directly into the GDS; if the PLC requires the alarm signal for control purposes, use a two-input one-output safety barrier to address this issue. The above are my personal opinions; I hope they are helpful to you.
This post was last edited by cww9521 on 2023-6-15 at 10:22. The safety verification requirements stipulate that the GDS must be independent of the process control system; it is recommended to install additional gas alarm terminals on site. The gas alarm functionality should be separated from the PLC system and connected to these terminal units, which in turn communicate with the GDS platform in the CCR. No more worries ahead; for reference only. For a detailed architecture, refer to the system configuration diagram examples in GB50493:
Yes, if the PLC outputs an AO signal in the 4-20mA format, the GDS system can receive that AO signal. Since the AO signal is an analog signal, it can generally be received and processed by various devices and systems. Furthermore, to ensure the accuracy and reliability of data transmission, it is also necessary to calibrate and tune the signals to ensure they meet the design requirements. .
Be careful about the installation location of this skid-mounted PLC; it must be in a safe area
The gas detector signal from the skid unit is now sent directly to the GDS system.
No. The detector probe of the GDS must be independent of the process control system. If the PLC is to use the data from flammable and toxic detectors, it is better to set up another set, with each set operating in its own system; of course, this incurs higher costs. Alternatively, the probe goes into the GDS, which sends a signal to the PLC.