Frequently asked questions about using inductive sensors are looked at in this section.
Inductive sensors offer many advantages over traditional mechanical switches.
Comparison of inductive sensor vs. mechanical limit switch
|Mechanical (Limit) Switch
|Fast signal processing
|The electrical output signals can undergo further processing directly in electronic circuits.
|Issues a mechanical signal, which is then transmitted electrically, hydraulically, pneumatically, or mechanically as required.
|Operation without touching the objects being measured.
|Operation only possible with mechanical contact: objects to be measured can be manipulated or obstructed.
|Quick detection and thus short response and switching times, i.e., high switching frequencies are possible.
|The mechanical sequence takes time and sets narrow limits on the maximum switching frequency.
|There are no moving contacts that can become contaminated or worn.
|Mechanical contacts can become contaminated and worn over time. The contact transition resistances can change unpredictably.
|Insensitive to contamination (humidity, oil, dust, etc.)
|Sensitive to contamination and humidity. Even slight contamination can lead to burn-off.
|Reliable signal generation
|The electronic output prevents contact bounce.
|Contact bounce may occur at signal output. As a result, a mechanical contact may supply multiple switching pulses per switch event.
|Low energy consumption
|Very small switching currents are also possible.
|The contact resistance and the risk of oxidation of the contact surface mean that a certain minimum current is necessary.
Simple integration into an application
|No calculation of the start-up curve is necessary.
|The start-up angle and start-up path must be calculated. Depending on the direction of actuation, different mechanical versions of the switch lever are required.
The wear resistance means that the switch points remain stable over time.
The number of switching cycles therefore does not affect the sensor service life.
Mechanically moving parts of the switch are subject to wear and lead to switching errors.
This means that the switching rate limits the switch service life.
|Applications with little space
|Extremely compact designs are possible.
|There are structural limits to the implementation of compact designs.
special designs as required
One design available for use in different applications requiring different movements.
Numerous sensor designs modeled on the mechanical limit switch assembly concept are available. This makes it easier to replace a mechanical limit switch with a sensor.
|Different applications require completely different designs or various sensing elements (rollers, tappets, levers, etc.).
Check all settings, properties, and distances relating to the sensor and the target. In particular ...
Check the sensor and the ambient conditions for possible interference.
In particular ...
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.
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.
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.
This depends on the type of digital input and the type of sensor you are using.
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.
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.
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 ʎdangerous (ʎd) is always the PFH value. The failure rate of the dangerous failures ʎdis the sum of the failure rates of the detected dangerous failures ʎdd and the undetected dangerous failures ʎdu:
ʎd = ʎdd + ʎdu
For single-channel systems, the probability of a dangerous failure is
PFH = ʎdu.
In SIL considerations from Pepperl+Fuchs for NAMUR sensors (N) and NAMUR sensors with safety function (SN), detectable dangerous failures ʎdd are not included, i.e.,
ʎdd = 0.
Therefore: PFH = ʎd
The various connection types can be quickly identified by referring to the type code.
|Sensor Identification (cf. Type Code)
If applicable, order designation "KK" in the second block of the order designation.
|Sensor without connection identifier at the end of the order designation.
|One of the following connector identifiers at the end of the order designation: "V1", "V3", "V5", "V13", "V16", "V18."
Identifier "B3" or "B3B" in the third block of the order designation.
|Sensors with FASTON® connector "V3" ... "V5" or sensors with solder connection etc.
Take a look at the range of Pepperl+Fuchs inductive sensors.