Logical issues with the pump shutdown valve in SIS interlocks
Thread Content
In typical SIS interlocks, sensors are used to detect signals before any action is taken. But in simple SIS interlocks of the type where a pump stop signal triggers the closing of a valve, are there any sensors involved? What is its source of signal?
Pumps have operation signals and current levels transmitted from electrical systems; some larger pumps may also have sensors for measuring temperature and vibration. Motors as well have sensors for temperature and vibration, and all of these can trigger SIS interlock actions.
Both the pump’s fault signal and stop signal can be used for interlocking. If these signal sources are frequency-modulated, they can be connected from the frequency modulation unit. If frequency conversion is not used, the power can only be obtained from contactors or thermal relays, etc. There are also those taken on-site, for pumps or motors, where a rotation sensor is installed. Once it is detected that rotation has stopped, an interlock signal is triggered
It can be understood by expanding the range of the signals; it’s not necessary to limit itself to things that can be seen with the naked eye such as liquid level, pressure, and temperature. Current, vibration, and so on can all serve as signals – anything that exhibits fluctuations can be considered a source of signal
The motor operation signal – the circuit associated with the motor requires a SIL rating, right, like in the case of motor relays
The pump stop signal can monitor the pump’s speed; a value below a certain threshold indicates that the pump has stopped； The valve can receive limit switch signals
The signals for pumps are usually on/off signals. For control valves that are pneumatic, there is an electromagnetic valve connected to the air supply to control the opening and closing of the valve; those that require feedback regarding the valve’s position are equipped with a mechanism for detecting the degree of opening
It usually comes from the electrical system; it’s a dry contact for the motor’s operation, DI
Signals are introduced into the DCS from the electrical cabinet; both fault signals and operational signals can be fed into the DCS. This requirement should be specified to the supplier during the design and selection of the electrical cabinet, so that the necessary wiring and contact signals are provided.
Current, pressure, flow rate, temperature (including monitoring of motors and materials), etc