A device that can protect a process by shutting it down at a preset “exceed condition”. Limit controllers work independently of the normal process controller, in order to prevent damage to equipment and products, or in some cases to prevent a hazardous condition. A fail-safe latching relay is fitted, which is reset by the operator once the process is returned to an acceptable condition.
Limit controllers are highly recommended for any process that could be damaged or become hazardous under fault conditions. Depending on the process and local regulations, they may need approval by a standards authority such as Factory Mutual in the USA, or comply with a safety directive such as EN14597 in Europe. Ensure that you select a product that has the required standards/approvals for you application.