Redundancy issue of I/O cards in DCS
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I remember that the IO cards of HONEYWEYY TDC3000 can achieve N:1 redundancy, with N seemingly being 1, 2, 3, or 6. Are all DCS IO cards currently equipped with 1:1 redundancy? Why?
Based on personal experience, the level of redundancy depends on the importance of the corresponding point: if the signal displayed on-site is simply fed into the system, there is no need for redundancy； If the signal at a particular point disappears, it can cause a failure of the entire system; therefore redundancy is necessary. Additionally, a system can be equipped with 10% to 15% more sensors as spares
Thank you to the person above; maybe I didn’t explain myself clearly. What I want to ask is: are there any DCS manufacturers that use IO cards of the N:1 type? I’ve seen several systems recently that use 1:1 redundancy; why isn’t N:1 redundancy adopted? Is it both economical and flexible – is it a technical issue or unstable usage?
Since DCS cards usually come with interlocks, and to prevent interlock actions resulting from damage to the cards, a 1:1 redundancy design is used; this allows for automatic switching in the event of a failure, and such switching occurs within milliseconds without causing any impact on the system.
The 1:1 redundancy you mentioned is what is commonly referred to as dual redundancy, and it is widely used in the DCS field. The power supply card, CPU card, and communication interface card in the control station are generally equipped with dual redundancy ； For I/O cards, it depends on the situation; control and interlock points should have dual redundancy as required, while monitoring points can be single ； N: 1 Haven’t heard of it; let’s hear what others think
N:1 redundancy was used in early DCS systems, as the hardware for those systems was quite expensive at that time. Later, it evolved into two forms: single-card setups and multi-card setups with 1:1 redundancy, and in recent years single-card setups have also been gradually phased out. Although 1:1 redundancy requires more hardware, hardware is now quite inexpensive; moreover, 1:1 redundancy significantly improves the reliability of the system. In chemical processing systems, IO cards used for regulating circuits are generally redundant. Functions such as device interlock protection are not implemented in the DCS; instead, they are handled by the SIS. In the SIS, the IO cards are also redundant to ensure reliability.