Problem with the bypass switch
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This post was last edited by zhoudingshengs on 2023-12-25 at 12:36. Please engage actively in the discussion: 1. When switching the bypass switch from the engaged position to the bypass position, it is necessary to \"close first and then open.\" If there is only a \"two-position\" switch available, how should it be wired to achieve this goal (the field device requires a 24VDC power supply when it is in normal operation)?
To address this issue, we can meet the requirement of \"closing first and then opening\" through the design of the control circuit. Since there is only a \"two-position\" switch available now, a relay or a time relay can be used to design a control logic. Specifically, first ensure that the switch at the bypass position is connected to a 24VDC power supply; this way, when the bypass switch is switched to the bypass position, the power can be supplied first through the activation of the relay, and then the power to the normal operation position can be disconnected. Such wiring ensures that the bypass switch follows a \"close first, then open\" operation sequence. .
The setting of the MOS (Maintenance Bypass Switch) in the SIS system, for reference.
The maintenance bypass switch is a mechanical switch (DI point); the switch key must be set to 1 in order to activate the interlock switch, while it must be set to 0 to disable the interlock. Why make it so complicated?
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