Concept of Product Lifetime of Non-contact Safety Switch

Necessity of considering the entire configuration

Non-contact safety switches are characterized by their structure, where the actuator and switch do not come into direct contact, resulting in no mechanical wear and the ability to maintain stable detecting performance over a long period of time. In particular, this advantage is evident in dusty environments and in equipment where frequent opening and closing operations are required.

On the other hand, it is important to consider not only detecting method, but also the entire configuration of the device when we think about "product lifetime" of safety switches.

- Difference in Detecting Method & Output Method -
Non-contact method, such as magnetic sensing, brings no mechanical wear on detecting unit. This is a big advantage with regard to long-term stability.

However, some safety switches have output with relay contacts. Relay contacts require consideration to operating conditions, because their electric durability varies as per voltage and current conditions and the type of loads.

- Electric Durability and Operating Conditions of Relay Contacts -
Generally, the following factors affect the lifetime of relay contacts:
・Applied voltage and current
・Resistive load or inductive load?
・AC or DC?
・Opening/closing frequency

Load on the contact can be particularly significant when it is inductive and DC loads. Therefore, more stable and long-term operation can be achieved by appropriate circuit design, including surge protection etc.

- Consideration for Safety Design -
For the design of safety-related control system, which is based on machine safety standard ISO 13849-1, reliability data such as B10d is used for evaluation.

However, these values also depend on use conditions.
Therefore, it is important to understand "detecting method" and "properties of output configuration" of each safety switch and verify PL of the entire system under appropriate operating conditions.

- Summary -
Non-contact safety switches are equipped with the great advantage to reduce wear on detecting part. On the other hand, when we consider their lifetime and reliability, it is necessary to make a comprehensive evaluation which includes properties of output part and actual use conditions as well as detecting method.

By selecting an appropriate model and designing circuits properly, it becomes possible to establish a safety system which works stably in long-term use.

For details about specifications and configurations of Line Seiki's safety switches, please refer to the product page.