There are considerable restrictions on the use of the PES, especially for the timing restrictions after faults have been detected. These timing restrictions are depending on calculations or applications. Refer to the detailed test reports of the respective TÜV test institute.

The reference list represents a common list of the working group "Safety Related PES" of IQSE (TÜV Product Service) and ASI (TÜV Rheinland). It has been compiled to give end users an overview of type certified PES. The list will be updated periodically. With this reference list both test authorities fulfil the requirement given by their European standard EN 45001 and EN 45011 accreditations to publish a list of tye approved systems.

All of the above mentioned PES assume that the zero signal of binary inputs and outputs represents the defined safe state for the application.

All of the above mentioned PESs with the system structures 1oo1 (1v1) and 1oo2 (2v2) and test reports dated 1989 or later, provide fault tolerance for the I/O-boards. If independent groups of I/O-boards have been defined during configuration or application programming, depending upon the product, a fault localisation on an I/O-board will lead to a shutdown of the associated safety related group only. Groups of I/O-boards can only be mutually independent, if the I/O-signals connected belong to independent parts of the application. Independent means that a part of the application has no safety relation with any other parts of the application.

Beginning with the publication of DIN V 19250 and DIN V VDE 0801 in January 1990 the classification and certification have been performed according to the safety categories of DIN V 19250 and the safety requirements of DIN V VDE 0801.

All executed certifications take into consideration requirements of a typical application standard, e.g. furnace control. As an alternative, typical application requirements (e.g. fault models, test methods, process reaction time, fault tolerance) are used. The specific application sectors covered by the certification are listed in the test report.