Questions regarding SIS interlock system

The diagram cannot be uploaded for now; it’s roughly like this: a low flow rate in the branch pipe of the heating furnace leads to the furnace shutting down as a result of the associated safety measures. In the interlock logic diagram, a low flow rate in this branch pipe results in the blower stopping as well. I would like to ask whether, if production is to resume and the blower does not return to its normal operating state via the SIS system, the heating furnace will also be unable to resume operation? I’m not sure if my explanation is clear; there are no images available for now, I’m sorry

Everything depends on the decisions regarding process and equipment safety. According to the interlock logic description in the process package, if manual reset or reset under other conditions is required, the interlock signal for stopping the blower is a hold signal; otherwise, it is a one-shot action.

The blower on the SIS does not return to its normal state – how can I start the blower? Without turning on the blower, it’s useless to just reset the heating furnace; the heating furnace can’t be started either. The blower here should be closely related to the heating furnace, right?

I know that the blower needs to be turned on first. What I’m asking now is, setting aside the furnace startup process and focusing solely on this interlock logic: if the blower doesn’t reset, can the furnace still reset? Is it logically impossible to reset?

I still don’t quite understand what you mean. I’m basically a complete beginner in this area; could you explain it more simply? Thank you

In short, it can only be determined by looking at the design diagram of the interlock logic. Different patent holders have different approaches to the same device design.

I see, thank you. Then I’ll look for that diagram

Following the approach used in power plant boilers, when shutting down the furnace, it is generally necessary to cut off the fuel supply while keeping the blower operating to purge the furnace. If the blower also fails, it should be started before the next ignition, and the furnace should be purged; once the purging is complete, the furnace failure signal will be automatically reset. The skip furnace signal does not have a manual reset button.

I don’t know the specific process; giving a general description may not be helpful. All interlocking actions can be roughly divided into two categories (of course, there are different ways of classifying them). Single-action and holding actions. A single action consists of sending a 0 pulse or a 1 pulse; in most cases, it is a 0 pulse that is used to activate the corresponding component, such as closing a valve or stopping a motor, etc. Maintaining the action means sending a continuous 0 signal or a 1 signal. For example, the interlock logic is used to switch the corresponding PID module to manual mode and set the PID’s AO value to 0%; this is usually a one-time action, after which manual operation is allowed to make changes. For another example, in some process packages, the interlock logic shuts down a shut-off valve by means of a hold signal; therefore, this valve cannot be opened until the interlock logic is reset.