Banner Safety Mat Monitoring Modules - Manual (Page 4)

Safety Circuit Integrity Levels
Safety circuits in international and European standards are segmented into categories, depending on their ability to maintain their integri-
ty in the event of a failure. The most recognized of these standards is ISO 13849-1 (EN954-1), which establishes five levels: Categories
B, 1, 2, 3, and the most stringent, Category 4.
In the United States, the typical level of safety circuit integrity has been called "control reliability." Control reliability typically incorporates
redundant control and self-checking circuitry and has been loosely equated to ISO 13849-1 Categories 3 and 4 (see CSA Z432 and ANSI
B11.TR4).
If the requirements described by ISO 13849-1 are to be implemented, a risk assessment must first be performed to determine the appro-
priate category, to ensure the expected risk reduction is achieved. This risk assessment must also take into account national regulations,
such as U.S. control reliability or European "C" level standards, to ensure the minimum mandated level of performance is complied with.
Fault Exclusion
An important concept within the category requirements of ISO 13849-1 is the "probability of the occurrence of the failure," which can be
decreased using a technique termed "fault exclusion." The rationale assumes that the possibility of certain well-defined failure(s) can be
reduced to a point where the resulting fault(s) can be, for the most part, disregarded – that is, "excluded."
Fault exclusion is a tool a designer can use during the development of the safety-related part of the control system and the risk assess-
ment process. Fault exclusion allows the designer to design out the possibility of various failures and justify it, through the risk assess-
ment process, to meet the intent requirements of Category 2, 3 or 4. See ISO 13849-1/-2 for further information.
Safety Mat Requirements
The following are minimum requirements for the design, construction, and installation of four-wire safety mat sensor(s) to be interfaced
with the SM-xA-5A Module. These requirements are a summary of standards ISO 13856-1, ANSI/RIA R15.06 and ANSI/B11.19. Review
all relevant applicable regulations and standards and apply the Module and any sensors in full compliance.
Design and Constructions
The safety mat system [Safety Module, sensor(s), and any additional devices] must have a response time that is fast enough (less than
100 to 200 ms, depending on the relevant standard) to reduce the possibility of an individual stepping lightly and quickly over the mat’s
sensing surface, without being detected.
For a safety mat system, the minimum object sensitivity of the sensor must detect, at a minimum, a 30 kg (66 lb.) weight on an 80 mm
(3.125") diameter circular disk test piece, anywhere on the mat’s sensing surface, including at joints and junctions. The effective sensing
surface or area must be identifiable and can comprise one or more sensors. The safety mat supplier should state this minimum weight
and diameter as the minimum object sensitivity of the sensor.
User adjustments to actuating force and response time are not allowed (ISO 13856-1). The sensor should be manufactured to prevent
any reasonably foreseeable failures (e.g., oxidation of the contact elements) which could cause a loss in sensitivity.
The sensor must meet a minimum environmental rating of IP54. When the sensor is specified for immersion in water, the sensor’s mini-
mum environmental rating must be IP67. Special attention may be required to the interconnect cabling; wicking action may result in the
ingress of liquid into the mat, possibly causing loss of sensor sensitivity. The termination of the interconnect cabling may need to be
located in an enclosure that has an appropriate environmental rating.
The sensor must not be adversely affected by the environmental conditions for which the system is intended. The effects on the sensor of
liquids and other substances which can be expected must be taken into account. For example, long-term exposure to some liquids can
cause degradation or swelling of the sensor’s housing material, resulting in an unsafe condition.
The sensor’s top surface should be a lifetime non-slip design, or otherwise minimize the possibility of slipping, under the expected operat-
ing conditions.
The four-wire connection between the Module interconnect cables and the sensor must withstand dragging or carrying the sensor by its
cable without failing in an unsafe manner (e.g., broken connections due to sharp pulls, steady pulls, or continuous flexing). If not, an
alternate means must be employed to avoid such a failure, for example, a cable which disconnects without damage and results in a safe
situation.
Installation
The mounting surface quality and preparation for the sensor must meet the requirements stated by the sensor’s manufacturer. Irregulari-
ties in the floor (or other mounting surfaces) may impair the function of the sensor and therefore should be reduced to an acceptable
minimum.
SM-xA-5A Safety Mat Monitoring Modules
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