Can the DCS perform an emergency stop when the pump is in local mode?
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This post was last edited by su_fairy on 2016-1-22 at 10:42. In DCS, the remote/local status of the pump is set, as well as the interlock logic; the pump stops automatically when the temperature of its stator bearings becomes too high. However, if the operation button on the pump at the site is set to the local mode, can the pump still be stopped when the stator temperature is high? If this can be achieved, is it a DCS configuration issue or a problem with the electrical circuits?
Generally, it’s not possible – the local mode cannot receive remote signals; however, this is not always the case with an emergency stop, as it depends on the drawings
Should I look at the electrical circuit diagram or the DCS configuration for the instruments?
Check the electrical system – see if the stop signal from the DCS can still control the motor after switching to local control
It can be stopped; the high stator temperature is a DCS interlock protection feature that is part of the configuration. The permissions for this are available at the engineer station, and they are higher than those granted to operators for local/remote switching； As for electrical appliances, it generally only provides protection for electrical components, such as protection against overload or no-load current
When the selection switch is set to local control, whether the pump can be stopped when the temperature is high depends on how the secondary control circuit diagram of the electrical cabinet is designed. If the pump shutdown contact for DCS shutdown is located before the selector switch, then regardless of whether the selector switch on the control panel is set to remote or local, DCS can shut down the pump.
It can be stopped; regardless of whether the selector switch on the control panel is set to remote or local, the DCS can shut down the pump.
Look at the primary control circuit diagram of the electrical system in this way. From what I’ve seen, if it’s connected to the electrical system via a single DO point, then once it’s set to local control, it can’t be stopped ； If it has two DO points, it can stop even when hit in place.
Can it stop? It doesn’t matter who says it; it depends on your settings. Whether local control or remote control has a higher priority than interlock protection is something that can’t be determined. No one can give you an exact answer to whether it’s possible to stop the operation. If the protection level of the electrical equipment design is higher than that for local and remote control, then the DCS must maintain the highest level of interlocks. It’s possible to perform a high-temperature shutdown even when cutting at the site
Generally, when it’s in local mode, the DCS shouldn’t be able to be shut down; otherwise, there would be no difference between remote and local modes. But ultimately, it depends on the electrical control circuit