Fault Repair/FAQ

Frequently asked questions about using inductive sensors are looked at in this section.

The Target Is Not Detected, What Am I Doing Wrong?

Check all settings, properties, and distances relating to the sensor and the target. In particular ... 

Sensor properties

• Operating distance: The operating distance can be found in the product technical data and the product marking.
• Switching element function: Check whether the specified switching element function is being observed: NPN or PNP? NC contact or NO contact?
• Electric voltage: The voltage should be between 10 V ... 30 V.

Target

• Material: The sensor only detects metals. Take the reduction factor into account!
• Size: The operating distance refers to the size of the standard target.
• Sensor-target relationship: Is the target moving past the sensor and at what speed? → Take the response curve into account: The switching frequency must not be exceeded.

Why Is the Sensor Switching Too Early?

Check the sensor and the ambient conditions for possible interference.
In particular ...

Sensor properties

• Switching element function: Check whether the specified switching element function is being observed: NPN or PNP? NC contact or NO contact?
• Installation conditions: Is the sensor flush or nonflush mounted according to the specifications in the technical data? Have the specified installation conditions been correctly implemented? 
• Recessed installation results in predamping of the sensor and an increase in the operating distance. It is essential to avoid recessed installation. It can lead to unpredictable sensor behavior. In some cases, lateral detection can also occur.

Electromagnetic influences

• Is the electromagnetic field of the sensor being influenced? By other electromagnetic fields? By a second sensor installed too close to it?

Ambient influences

• Metal interference: Check whether there is another metal object in the vicinity.
• Contamination: Check the sensor for contamination. If necessary, clean with a cloth and a nonabrasive agent.

Is the Selected Sensor Chemically Resistant to a Particular Cleaning Agent, Coolant, or Lubricant?

Unfortunately, we cannot give a definitive answer to this question. 

This is because the composition of cleaning agents, coolants, and lubricants, i.e., the formulation, is known only to the relevant manufacturer. Lubricating oils usually contain additives, which, even in small quantities, can change the chemical behavior of the lubricating oil. Even if the sensor housing material specified in the technical data promises to be oil-resistant, the additives can make the lubricant aggressive as a whole.

It is therefore essential to carry out your own tests to check chemical compatibility. Please note that the manufacturer of a cleaning agent, coolant, or lubricant can change its formulation without notice. This can cause a combination of materials that has worked for a long period of time to suddenly stop working.

Must Existing EC-Type Examination Certificates Issued in Accordance with EU Directive 94/9/EU Be Replaced by New EU-Type Examination Certificates, which in turn Cite EU Directive 2014/34/EU?

The new EU Directive 2014/34/EU provides clear information in this regard under Article 41, paragraph 2, and states that EC-type examination certificates issued under EU Directive 94/9/EU remain valid.

Citation 2014/34/EU
Article 41 Transitional Provisions

(1) Member States shall not impede the making available on the market or the putting into service of products covered by Directive 94/9/EC which are in conformity with that Directive and which were placed on the market before April 20, 2016. 

(2) Certificates issued under Directive 94/9/EC shall be valid under this Directive.

Can I Connect a Sensor with Two-Wire Function to the Digital Input on my Controller (PLC)?

This depends on the type of digital input and the type of sensor you are using. 

Individual types
Type 1: Digital inputs for mechanical contacts and three-wire sensors. Sensors with two-wire function cannot be connected to type 1 inputs.

Type 2: Digital inputs for two-wire sensors. This input type is suitable for signals from semiconductor switches, e.g., two-wire sensors according to the standard for proximity sensors (IEC 60947-5-2). These inputs have an increased current consumption of up to 30 mA for two-wire sensors per channel and are therefore more suited for PLC modules with a lower channel density.

Type 3: Digital inputs for two-wire and three-wire sensors. Type 3 digital inputs have a lower power consumption than type 2 digital inputs. These inputs are intended for the use of three-wire sensors according to the standard for proximity sensors (IEC 60947-5-2). Sensors with two-wire function can also be used on type 3 digital inputs if they have a low current in the off state.
For this case, Pepperl+Fuchs has developed sensors with two-wire function and extremely low residual current. They contain a capital "L" in the description of the two-wire output (see output type "Z4L" or "Z8L"). The "L" stands for "Low", i.e., low residual current. The residual current via the open contact is between 100 µA ... 200 µA, compared to 0.4 mA ... 0.6 mA of conventional two-wire sensors from Pepperl+Fuchs. These two-wire sensors can replace three-wire sensors on type 3 digital inputs of programmable logic controllers (PLCs) according to IEC EN 61131-2.

Does Pepperl+Fuchs Offer Inductive Sensors According to NEC 500?

Inductive sensors according to NAMUR from Pepperl+Fuchs are suitable for use in Class I - III, Division 1; see the information in the Control Drawing, which can be downloaded from the Pepperl+Fuchs website.

Background knowledge ...
NEC 500 is a combination of the designation for the only legally binding standard for electrical equipment in the USA (the NEC) and an article (500) thereof. The abbreviation "NEC" stands for National Electrical Code and is considered law in the USA as NFPA 70 (National Fire Protection Association No. 70). Article 500 of this Code describes the classification of explosion-hazardous areas according to Classes and Divisions in the USA. Similarly to the zone classification according to Directive 2014/34/EU in Europe, plants are divided into different areas—Classes and Divisions—according to the duration and frequency of the occurrence of a hazardous potentially explosive atmosphere.

Can Inductive NAMUR Sensors with SIL Rating (e.g., SIL 2) from Pepperl+Fuchs Be Used in High Demand Mode? Where Can I Find This Information?

Inductive sensors from Pepperl+Fuchs may also be used in high demand mode. However, the PFH value is not always included in the SIL documents from Pepperl+Fuchs (e.g., Exida report). Nevertheless, the value can be deduced.

Deriving the PFH value—in detail
High demand mode refers to an operating mode with a high demand rate or a continuous demand on the safety instrumented system (SIS). The key characteristic for assessing an SIS in high demand mode is the PFH value (PFH= probability of failure per hour). The PFH value indicates the probability that an SIS will perform its function over a specified period of time (e.g., one hour). Inductive sensors from Pepperl+Fuchs may be used in high demand mode; however, the PFH value is not always included in the SIL documents from Pepperl+Fuchs (e.g., Exida report). Nevertheless, the value can be deduced:

Assuming that the user is building a single-channel system, the value for ʎ_dangerous (ʎ_d) is always the PFH value. The failure rate of the dangerous failures ʎ_dis the sum of the failure rates of the detected dangerous failures ʎ_dd and the undetected dangerous failures ʎ_du:

ʎ_d = ʎ_dd + ʎ_du

For single-channel systems, the probability of a dangerous failure is

PFH = ʎ_du.

In SIL considerations from Pepperl+Fuchs for NAMUR sensors (N) and NAMUR sensors with safety function (SN), detectable dangerous failures ʎ_dd are not included, i.e.,

ʎ_dd = 0.

Therefore: PFH = ʎ_d