Training manual. Connection technology ± ±²

Transcription

1 Connection technology º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³

2 You will find further information, data sheets, prices etc. at: Training manual connection technology for binary sensors (March 2003) H:\STV\INTERN\Sc- und Se-Unterlagen alt\deutsch\sc\sc100\sc100.doc :24 Guarantee note This manual was written with the utmost care. However, we cannot assume any guarantee for the contents. Since errors cannot be avoided despite all efforts we appreciate your comments. We reserve the right to make technical alterations to the products so that the contents of the training manual may differ in this respect.

3 Connection technology Contents 1 Introduction Proximity switches in industrial processes Layout On the contents 6 2 The basics Binary sensors wire units wire Supply Further electrical characteristics Analogue sensors Sensors with a built-in interface 18 3 Notes on the practical use Supply Circuits General Series connection Parallel connection Mechanical and electronic switches Electrical data 24 Annex 25 Glossary of technical terms 26 Index 28 3

4 1 Introduction 1.1 Proximity switches in industrial processes Sensors Automated production processes require sensors to supply information. They provide signals about positions, limits, levels or serve as pulse pickups. Without reliable sensors even the best controller is not able to control processes. In general, all these sensors consist of two components: The first one registers the change in the physical conditions (basic sensor), the second one converts the signals of the basic sensor into electrical output signals (signal processing). Figure 1: Structure of a sensor In general, a distinction is made between binary sensors which provide a definite high-low signal and analogue sensors which are preferably used for temperature, distance, pressure, force measurement, etc. The sensor supplies an analogue signal which is further analysed for measurement and control. Binary and digital In order to avoid misunderstandings this is to give a short explanation of the difference. Binary means "two values" also in the original sense of the word. An analogue signal which can have any value within certain limits is often digitalised today so that it can be further processed in electronic controllers. This is done via an A/D converter (analogue into digital). It divides the analogue signal into steps. The number of steps results from the number of bits used. One bit can only have two values, but with 8 bits there are already 256, with 10 bits there are 1024 steps. This is also called resolution. Fewer than 8 bits are seldom used because the resolution is too coarse in this case. More than 12 bits are also rarely used because it does not make sense if the resolution is much higher than the measuring accuracy. º «¼»² ± ²¼ ¼ ¹²± ½»³ 4 ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³

5 Connection technology Shaft encoders are an exception. They provide digital signals from the start, see Training manual Shaft encoders. This text deals especially with binary electronic sensors as replacement for mechanical switches. It is to give an overview of the characteristics and criteria for the use of such sensor systems. There are many names for inductive and capacitive sensors: Proximity switch, initiator, inductive sensor, non-contact position sensor, but there are also manufacturerspecific names like e.g. efector (registered trademark of ifm electronic gmbh). The expression proximity switch, however, is the standard term which will be used in the following. Division With the initially confusingly large number of sensors with different operating principles it helps to keep the overview if they are divided according to their applications. Position This can mean simple presence, reaching of an end stop or end position, exceeding or not reaching a level etc. Thus, in this application more mechanical movements are monitored. In most cases binary sensors are used. They are also called limit switches. Typical examples are inductive and capacitive proximity switches, photoelectric sensors etc. Shaft encoders can also be included. Fluids In case of liquid and sometimes also gaseous media levels, but also other parameters are monitored, like exceeding or not reaching a limit speed, a limit pressure, a limit temperature etc. Thus fluid sensors are also often used as binary sensors. Analogue output signals, however, are more important. Typical examples are level, flow, pressure, and temperature sensors. This division should not be seen as a rigid scheme. There are also borderline cases, e.g. a binary level sensor can be seen as position sensor or as fluid sensor. Binary sensors are mainly connected to electronic controllers. There are also cases, however, in which other loads are switched or in which attempts are made to connect the sensors to each other (connection in series or in parallel). This manual is to give useful information on this topic. Further electrical data and characteristics of binary and analogue sensors will be discussed. There is a series of electrical characteristics which are the same for all electronic, binary position sensors, e.g. inductive and capacitive proximity switches, photoelectric sensors, etc. This is also valid for analogue sensors. Therefore they are discussed in detail separately. Outputs To switch the output signal semiconductor switches like transistors and thyristors are now widely accepted on the market. They have clear advantages over mechanical switches as regards life, the number of reliable switching operations, the switching frequency, and the bouncefree switching characteristics. The few disadvantages, i.e. leakage current in the switched-off state, voltage drop in the switched state and higher sensitivity as regards overvoltage and overcurrents can usually be tolerated or to a large extent 5

6 avoided by means of suitable protective measures. This manual is to provide helpful information. 1.2 Layout For a better understanding a few explanations regarding terms used in the text will be given to make reading the text and location of information easier. Keywords What does FAQ mean? Keywords are given in the left margin. They refer to the topic to be dealt with in the following section. This means Frequently Asked Questions. This term is also used in modern electronic media. Almost every beginner has the same questions. Occasionally they will be put before a section instead of a keyword. To differentiate them from simple keywords, they are written in italics. (4) A figure in round brackets in the left margin refers to a formula used in the following text, e.g. see (4). Of course these formulas are not meant to be learnt by heart. They are to make understanding the subject easier because a formula, similar to an illustration, describes a relation more briefly and clearly than many words. 1.3 On the contents This manual is to give basic information on (binary) proximity switches. Important terms and connections will be explained, the state of the art will be described and technical data of ifm units will be presented. This results in the following structure. 1. Introduction The introduction is followed by the chapter: 2. The basics A few basic terms and their context will be described. Consequences for practical use will follow in the next chapter: 3. Notes on the practical use The requirements as regards current and voltage supply are stated. Connection in series or in parallel of electronic sensors should be avoided if possible. If it is unavoidable you can refer to the notes in chapter 3. The knowledge of these features, the advantages and disadvantages, is a prerequisite for successful use. Annex Much success! This manual is to also help you with your self-study. Therefore important terms will be explained again briefly in the short technical glossary. The points which are important for ifm sensors will be discussed in detail in the preceding chapters. The index helps to look them up. The type key and the code for the production date will also be briefly presented. These basics should enable everybody to benefit from the chance that electronic sensors offer and to use them successfully. º «¼»² ± ²¼ ¼ ¹²± ½»³ 6 ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³

7 Connection technology 2 The basics The physical basics are not treated in this chapter; this is done when the individual sensor types are discussed. Here the basics of connection technology are explained and classifications are made. 2.1 Binary sensors Binary sensors can be compared with mechanical switches. The characteristics of these systems are explained in detail e.g. in the Training manual Inductive proximity switches. If you compare all features you can see clearly that electronic proximity switches have advantages over mechanical limit switches so that the use of non-contact sensors is an advantage for the user in any case. It increases the reliability of the plant while at the same time reducing the operating costs. Thus it results in increased competitiveness. Figure 2: Mechanical switch These reasons have led to the electronic proximity switch replacing the mechanical limit switch to a large extent in industrial applications. It has specific characteristics, however, which have to be taken into account. Proximity switches are offered in the so-called 2-wire, 3-wire and (for special cases) 4-wire technologies. 7

8 wire units This is the system which is most similar to the mechanical switches (shown as symbol in Figure 3). The load is connected in series to the sensor. Figure 3: 2-wire Voltage Current For 2-wire switches the operating voltage is the common voltage available for the connection in series of the proximity switch and the load. In this case a slightly lower voltage is applied to the connections of the proximity switch because some of the voltage already drops at the connection, depending on the internal resistance of the load. An important criterion in this case is the voltage drop over the sensor in the switched state. It can be found in the data sheet, see e.g. and depends on the type. Typical values are: 2.5 V for current DC units 6.5 V / 6 V for UC units in AC / DC operation 8.5 V for AC units These three types are described in In the unswitched state the leakage current which the electrical circuit requires for its own operation flows over the load. Depending on the sensitivity of the load this can for example lead to problems (cf. connection in series and parallel, and 3.2.3). For older units it was a few ma. If required, a resistor or an RC combination must be switched in parallel to the load. º «¼»² ± ²¼ ¼ ¹²± ½»³ 8 ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³

9 Connection technology Figure 4: Leakage current DC Figure 5: Leakage current AC In the past usually 3-wire units were used to ensure optimum protection against incorrect switching, e.g. in connection with a plc. For newer units, especially the quadronorm units, it was possible to reduce the leakage current to typically 0.4 to 0.6 ma. The voltage drop in the switched state could also be reduced. There is a trend to replacing 3-wire units with 2-wire units. This enables considerable savings as regards cabling. It has to be considered, however, that especially 2-wire units cannot be compared with mechanical switches. Each step of development, however, tries to make them more similar. 9

10 wire With 3-wire switches the operating voltage is applied between +UB and 0 V and the switching signal is led to the load via an additional wire. Figure 6: 3-wire Voltage Current 4-wire The voltage drop in the switched state is considerably lower, it is typically 1 V. In the unswitched state the output then is virtually de-energised, no current can flow except for the leakage current of a few µa of the transistor and the protective circuitry. The own requirement of the sensor is not important here. It has to be taken into account, however, when dimensioning the power supply. An exception are some 4-wire units. They have two complementary outputs which can both be used for normally open and normally closed function. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 10

11 Connection technology Figure 7: 4-wire Supply This is an overview and an explanation of the designations. For further information see 3.1. Basically there are 3 types: DC units AC units UC units This is the most common type. The operating voltage for sensors which is common in industrial installations is 24 V, usually DC. There are also installations, however, which are operated with alternating voltage. Other nominal operating voltages like 12, 48 or 60 V are found as well. In practice it is not only the nominal voltage which has to be taken into account, but also the operating voltage range in which the sensor works reliably (see 3.1.). It can also be found in the data sheet. Typical values are: V, V, V, V. A wide range is interesting for several reasons: The units can also be operated with unusual voltages, e.g. with a 12 V battery. In industrial applications voltage fluctuations are to be expected. This should not lead to faulty signals. Usually current and voltage fluctuations of any kind are permissible with a DC supply, if the values are not below or above the minimum and maximum voltage of the indicated operating voltage range. This can be 230 V or 115 V. The importance of these units is decreasing, however. If no AC unit is available a UC unit (see below) can be used instead. UC stands for universal current. These units can be used for direct current or alternating current. Typical ranges are V AC/DC. If units for both voltages are used it simplifies storage of spare parts for the user. 11

12 The total harmonic distortion (interference in the range of more than 50 Hz) should not exceed approx. 10% for AC units. The standard IEC defines utilisation categories. They define switchgear in order to better describe the characteristics which are typical of these categories. Utilization categories They are listed and explained in the table below. Switch elements Category Typical applications: Alternating AC 12 control of resistive loads and solid state loads voltage AC 140 control of small electromagnetic loads with holding current < 0.2A, e.g. contactor relays Direct voltage DC-12 control of resistive loads and solid state loads DC 13 control of electromagnets Category AC-140 applies to efectors in AC/DC version, category DC-13 applies to 2 and 3-wire DC efectors and category DC-12 to NAMUR types. Different types of application are permissible if it is agreed between ifm as manufacturer and the user or if it is mentioned in the catalogue. For further information about noise immunity see the Training manual CE marking Further electrical characteristics Energy requirement Load capacity Protective circuitry Short-circuit protection º «¼»² ± ²¼ ¼ ¹²± ½»³ Energy is of course needed for the own supply of the electronics. As an example the 24 V DC units are described assuming that the 24 V are constant. For 2-wire unit the leakage current flows via the sensor (and the load) in the open condition, see It is typically at approx. 0.5 ma. For 3-wire units the current consumption has to be taken into account, see It is typically at approx. 15 ma. This results in typically 10 mw for 2-wire units and 150 mw for 3-wire units. This considerable difference is a further reason why one should consider using 2-wire units instead of 3-wire units. This concerns mainly standard inductive sensors. For photoelectric sensors this is of course not easily possible. In this case even higher values have to be expected. The load capacity of the sensors cannot be compared with the load capacity of electronic relays, among other things due to the housing type. The maximum current of DC units is between 100 and 400 ma, depending on the type. For UC units the maximum current is different depending on the operating voltage. Typical values are e.g. 100 ma DC and 350 ma AC. Most DC units have short-circuit protection. In this case they are also reverse polarity and overload protected. In technical terms the short-circuit protection of proximity switches is normally designed as follows: A precision resistor is inserted into the load circuit and the voltage drop at this resistor is monitored. If the current exceeds a fixed limit value the switch is blocked. ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 12

13 Connection technology Two disadvantages of the short-circuit protection have to be mentioned: On the one hand, the resistor causes a little higher voltage drop in the switched state than a comparable proximity switch without short-circuit protection. On the other hand, the short-circuit protection may respond unintentionally, for example when there are temporary higher switch-on currents(contactors, incandescent lamps), capacitive loads (e.g. when operated with long cables)or transients. The latter case leads to sporadic interferences which are difficult to locate. For this reason some users refuse to use units with short-circuit protection. Should the sensor be destroyed due to overload the fault is localised and appropriate measures can be taken. How does the proximity switch know after being blocked by the shortcircuit protection and with (almost) no current flowing through the load that the short circuit is removed and it can switch on again? There are two different operating principles on the market: For principle 1 the proximity switch remains blocked after the short circuit has been noticed until the operating voltage is interrupted which leads to a resetting of the short-circuit protection circuit. According to the EN switches which work according to this principle can only be called "partially short-circuit protected" because action is required to restore operation. For principle 2 the switch is only blocked for a certain period of time (typically approx. 100 ms) and is switched on again automatically after this period. If there is still a short circuit the current at the precision resistor will again exceed the defined limit value and block the switch again after which the cycle starts again ("automatic checking"). If the short circuit has been removed the proximity switch is operational again immediately (i.e. after 100 ms at the latest) without any further measures. This is the principle of ifm efectors which are protected against short circuits. 1 short circuit 2 short circuit removed Figure 8: Automatic checking Proximity switches fitted with this type of short-circuit protection comply with the requirements of DIN as regards short-circuit-proof electrical equipment. Polarity As mentioned above semi-conductor outputs have considerable advantages over mechanical contacts, but other characteristics have to be taken into account, e.g. the polarity. In many countries pnp-switching 13

14 units are common, in some countries however, npn-switching units are common. In both cases reverse polarity is possible of course due to a wiring fault. Reverse polarity protection Reversed connections If a proximity switch is protected against reverse polarity its connections can be reversed without any damage to the switch. It cannot be expected, however, that the switch functions in all these cases. There are only two ways of connecting a 2-wire proximity switch so that an error can be handled easily (for example by means of a built-in diode in series with the switch which blocks when the polarity is wrong or by means of built-in rectification which permits either polarity). With 3-wire systems there are a number of ways to make a wrong connection of at least 2 wires. The reaction of the switch to the wrong connection, i.e. whether it remains open or permanently closed depends on the type of protective circuitry. A detailed example is given in the table: Connection of the cable brown black blue Reaction of the efector L+ load L- normal function L+ L- load short-circuit protection is activated load L+ L- switch blocked, no function load L- L+ switch blocked, no function L- load L+ switch blocked, no function L- L+ load switch blocked, no function Switches protected against reverse polarity must also be short-circuit proof for 3-wire units because otherwise reversing the output and the 0 V wire would destroy the switch. Overload protection There is a variable difference between the maximum current which is permissible for a certain proximity switch according to the data sheet and the current at which the short-circuit protection becomes effective. This overload range is due to component tolerances. Normally, the proximity switch should not be operated in this range because the data specified by the manufacturer in the data sheet are only guaranteed up to the nominal current. Furthermore the overload range usually depends on the ambient temperature (this effect is called "derating") and varies from one unit to the next. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 14

15 Connection technology I L continuous current rating [ma] T ambient temperature [ C] 1 AC units 3 IF / IFA AC 2 AC/DC for AC 4 short-body types IFB, IGB, IIB Figure 9: Derating A proximity switch is protected against overload if it can be operated in this current range for any period of time and over the whole temperature range. Thus the switch can be connected to any resistor between 0 and without being damaged. If the short-circuit protection operates to the automatic checking principle there is, however, the reservation that normally, in the case of high inductive loads, the overload protection cannot be ensured without an external no-load diode. Standard sensors All efectors of the ifm standard range having the letter "K" at the 11th position of the type key are short-circuit protected according to DIN They are also protected against overload over the whole permissible temperature range, see They are also capable of switching capacitive loads of at least 20 nf in parallel to an ohmic load. As a rule, this value corresponds at least to a cable length of 200 m. The short-circuit protection has been designed following the automatic checking principle. For inductive loads with a time constant >> 1 ms the proximity switch may get damaged in the event of an overload without external protection. When the short-circuit protection circuitry was rated special care was taken that transients frequent in industrial power supplies do not trigger the short-circuit protection. Thus the short-circuit protection does not impair the high noise immunity of the efectors. Order of connection AC and AC/DC switches can be connected in either way. They are fully operational with both connections. All efectors are protected against reverse polarity. So quadronorm switches cannot be damaged by false 15

16 connection either. However, the way they are connected determines their output function. Figure 10: Connection efector quadronorm One goal of developing the efector quadronorm switches was to provide a unit for as many applications as possible. By simply reversing the connection wires the functions normally closed and normally open are reversed. If the connecting wires are inadvertently reversed, this leads to an undesired change of these functions which can cause spurious operations. To prevent this source of error non polarised switches were developed. ¾µ ¾µ Ô õ Ô ó Figure 11: Connection unipolar efector 2-wire DC units except quadronorm switches (programming by reversing the connections) are permanently conductive at the terminals if the polarity is reversed. Output function Some units are available as normally open or normally closed units. For many units a programming possibility is connected additionally to the º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 16

17 Connection technology evaluation stage. In this case the switching function normally open or normally closed can be selected. For quadronorm units this is made by reversing the wires (see Figure 10). For 4-wire units (see 2.1.2) both functions are available simultaneously. 2.2 Analogue sensors The processing of analogue signals was already practised before binary electronic proximity switches replaced the mechanical switches. Thus this application has been known for a long time. In this case there are fewer special characteristics to be taken into account. Current and voltage outputs have to be differentiated. The voltage output is used more seldom in order to avoid measuring errors due to the voltage drop in the wires. Current There are two variants: ma and ma. The advantage of the second solution is the additional possibility of wire break monitoring. This is preferred in practise. Thus most of the units with current output are only available in the version ma. Simple sensor systems, so-called transmitters, virtually consist only of the transducer which transmits an analogue signal. Processing and implementation are carried out in the connected units. Modern sensors with microprocessor integrate this function and help to save production complexity and thus costs. Some of them also allow an adaptation of the measuring range to the application. Thus for e.g. temperature sensors the lower limit of 4 ma can be assigned to a temperature of 0 C and the upper limit of 20 ma to a temperature of 100 C (see Training manual Temperature sensors). The control and display unit to which the analogue output is connected has of course an input resistor. If the resistance is low, even in case of a short circuit, the current regulator should keep the current constant. More critical is the case of too high a resistance. The current regulator in the sensor cannot increase the required voltage to any value. Thus there is an upper limit for the resistance, for efector 600 e.g. max Voltage Supply voltage The range of V is common. This is the opposite of the current output. The resistance must not be too low, otherwise the voltage regulator is not able any more to maintain the voltage. In case of a short circuit the voltage output is blocked. For efector 600 e.g. the resistance should be at least The importance of the voltage interval in which the sensors function reliably was already explained in the chapter about binary sensors, see There are types, especially among the fluid sensors, which are equipped optionally with binary switching outputs, e.g. for triggering a pump or a heating system or with analogue outputs (or mixed), e.g. for a control module. If such a unit has an analogue output the requirements as regards the supply voltage are higher. Thus the permissible range is often smaller than for a unit with binary outputs. 17

18 2.3 Sensors with a built-in interface These sensors are only mentioned here for the sake of completeness. There are e.g. inductive proximity switches with AS-i interface or shaft encoders with PROFIBus interface. Thus they have no switching outputs in the conventional sense. The connection must be made according to the specifications of the bus system. Any standard sensor can also be connected to a bus system, but this requires for example an I/O module. In this sense each sensor "can be connected to a bus system": This is not the same as "with a built-in interface". Intelligent Sensors with a built-in interface often belong to a group called intelligent sensors. This means sensors which provide more information than "object detected" or "object not detected". Photoelectric sensors can signal e.g. that they are soiled. Capacitive sensors can be adjusted by means of a pulse on the programming wire in such a way that the environmental influences are compensated for. With conventional connection this means an additional output or input, an additional wire, more wiring complexity...thus it is not often used. For sensors with a built-in interface, however, the complexity is not higher. Here the sensor can easily be monitored as regards wire break or readiness for operation. It is to be expected that these sensors with a built-in interface will be used more and more in future. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 18

19 Connection technology 3 Notes on the practical use This chapter deals mainly with binary sensors. 3.1 Supply For noise immunity and preventive measures in case of interference see the Training manual CE marking. Electronic sensors have become less sensitive to interference over the years. Their use has become a matter of course. The data sheet is not even consulted. It may also happen that concerning the permissible operating voltage range (see 2.1.3) the addition "including residual ripple" is not considered. Residual ripple This can sometimes cause interference. It means that also short spikes or dips of the supply voltage must be within the permissible range. Otherwise reliable signals cannot be ensured. A quality power supply which supplies a stable and smooth supply voltage for DC should also be used for the supply of the periphery,i.e. the sensors. For AC or UC units there should not be too much interference of the alternating voltage either, of course. Figure 12: Residual ripple and total harmonic distortion Furthermore, when planning it should be taken into account that not only loads, e.g. valves have to be supplied, but also the sensors. The requirement for inductive sensors is in the ma range. Optical sensors require a little more current simply to produce light. Especially for fluid sensors with more complex conditioning and processing of the measuring 19

20 signal the current consumption can exceed 50 ma. If the power supply is underdimensioned there is the risk of falling below the permissible limit of the supply voltage in case of a voltage dip. This can lead to wrong pulses. Periodic higher-frequency AC voltage parts are called residual ripple in case of DC voltage. For AC voltage they are called total harmonic distortion. There are also different types of fluctuation with AC. Figure 13: Voltage fluctuations AC 3.2 Circuits General Electronic units are different Clarity The characteristics which have an unfavourable effect with mechanical limit switches, like wear and tear and corrosion, have led to their replacement by electronic proximity switches as mentioned above. The replacement of contactor controllers by electronic controllers is a similar case. The current solution has considerable advantages. It has to be taken into account, however, that electronic sensors may react differently from mechanical switches. This is especially important in the contexts described below. It is state of the art in automation technology to combine the binary signals provided by the sensors in the plant in an electronic controller. As a rule it is avoided when working with a plc to externally form logical combinations by means of series or parallel connection because this makes tracing of errors more difficult in case of a fault. Sometimes, however, this is done. Thus the wiring complexity in a large-scale plant can be reduced if the switches are connected logically. It is also possible that several switches must be connected together because of modifications to existing plants. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 20

21 Connection technology Time characteristics Better not! Usually electronic proximity switches have considerably shorter switching times than mechanical switches, but they also have a power-on delay time which is much longer than the switching time. The time which elapses between the application of the operating voltage and complete readiness for operation is called power-on delay time. This time must be taken into account if sensors are only supplied with operating voltage after another sensor is switched. These times can add up if several sensors are connected in this way. For reasons of clarity and because of the characteristics described below we advise against the connection of binary electronic sensors with each other! This should only be done if it cannot be avoided, but the notes concerning the maximum number must be observed. It is absolutely necessary to make extensive tests and test runs Series connection 2-wire units In principle, the series connection of 2-wire standard inductive units is not recommended as a safe function cannot be guaranteed. It must be considered that the voltage drops of the proximity switches add up and so less voltage is available to the load. When switching inductive consumers the phase shift becomes effective. If all these points are considered, a maximum of 2 to 3 proximity switches can be connected in series depending on the type. ifm electronic offers some special units for such applications. For information please contact the respective departments. Figure 14: Series connection 2-wire In principle, the series connection of 2-wire optical units is not recommended. As the closed-circuit current consumption of the units can be different the unit with the higher closed-circuit current is not supplied sufficiently which causes problems. At the same time the switched unit needs a higher current; this leads to the output status indication not being lit if one of the units has not switched. In principle series connection is not recommended for the units of the new generation with microprocessor either. 21

22 3-wire units If 3-wire proximity switches are connected in series, the voltage drops on switched units between 1 and 2.5 V add up. Care must be taken that the load can still be operated correctly with the remaining voltage. The first proximity switch must be capable of switching the current consumption of all subsequent proximity switches in addition to the load current. As the operating voltage of the proximity switches connected in series can be turned on or off, the power-on delay time must be considered (up to several 100 ms). If these points are taken into account, a maximum of 5 to 10 proximity switches can be connected in series depending on the type. Figure 15: Series connection 3-wire In principle, series connection of 3-wire optical units is not recommended. Due to their system, photoelectric components have a high inrush current. This current causes triggering of the short-circuit protection of the first sensor connected. We would like to point out that the circuit logic has the same result if parallel connection is selected instead of series connection. The switching function "normally open" must be inverted in this case, i.e. it must be replaced by "normally closed" Parallel connection 2-wire units If 2-wire proximity switches are connected in parallel, the leakage currents of all non-switched units add up. The sum of the leakage currents must be clearly below the holding current of the load (which is important for the connection to programmable controllers). It also has to be taken into account that when one proximity switch is switched the operating voltage is taken off the switches connected in parallel so that they can no longer indicate their true damping status. (Exception: quadronorm units). If all these points are taken into account, a maximum º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 22

23 Connection technology of 5 to 10 proximity switches can be connected in parallel depending on the type. As photoelectric units generally have a high leakage current the connection in parallel of 2-wire photoelectric units is not recommended. When a unit is switched through, operating voltage is taken off the other switches so that the function of the units can be impaired. Figure 16: Parallel connection 2-wire 3-wire units: It is possible to connect a maximum of 20 to 30 three-wire switches in parallel without any problem (depending on the type). The only factor which must be considered is that the (very small) leakage currents of the switches in the unswitched state add up. Decoupling diodes are only required for output stages without open collector circuit. The current consumption of all non-switched units adds up. Proximity switches can be used together with mechanical switches (taking into account 3.2.4). Figure 17: Parallel connection 3-wire units There is no objection in principle to the parallel connection of 3-wire photoelectric units. The number of possible components depends on the type. In principle, this is also valid for function check outputs. 23

24 3.2.4 Mechanical and electronic switches +24 V S1 S2 Load 0 V Figure 18: Mechanical and electronic in parallel An especially critical case is the connection in parallel of a mechanical proximity switch, S1, and an electronic proximity switch, S2. In this case the arguments of have an even stronger effect. Let us have a closer look at the chronological sequence of events: 1. The mechanical switch is closed. Thus the electronic proximity switch has no operating voltage. It is not operational. 2. The proximity switch is damped. Because of 1., however, it does not react. 3. The mechanical switch opens. The power-on delay time of the proximity switch elapses, see Only when the power-on delay time has elapsed, the proximity switch switches. The connection of electronic and mechanical switches can have effects which are not easily forseeable. For reasons of safety this should not be done. 3.3 Electrical data Some data have already been mentioned in the respective contexts. Here they are to be summarised and completed. Power The power consumption which modern proximity switches require for maintaining their sensor function is very low. For 3-wire switches it is approx W; for 2-wire switches there are efectors with power consumption as low as W (3 mw). Any resistive load can be connected to a proximity switch within its nominal data. With the technical data which are common today the use of programmable controllers is possible without any restrictions. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 24

25 Connection technology Inductive loads Inductive loads up to a cos of 0.3 (like e.g. solenoid valves) do not cause any problems either as long as the limit currents are not exceeded. In theory difficulties can arise in case of high switching frequencies which, however, are not common in this context. Usually the low leakage current which flows via the load in the unswitched state as well as the voltage drop over the switch in the switched state do not impair the correct function. Incandescent lamps With incandescent lamps the high inrush current which flows in case of cold filaments must be taken into account like with AC relays or AC contactor relays which have a considerably lower impedance before the contact is closed. ÝØïæ ðòîðê æîð³ Figure 19: Inrush current of an incandescent lamp ÝØïæ ðòîðê æîð³ Figure 20: Inrush current of a contactor Thus some types of switches (especially AC switches) are rated according to the corresponding standard in such a way that they can have six times the nominal current for a short time. For switches with short-circuit protection it must be ensured that the inrush current does not lead to triggering of the short-circuit protection. Incandescent lamps can be preheated by means of a resistor in parallel to the switch if necessary, in order to reduce the inrush current efficiently. As mentioned in these characteristics are important for the utilisation category of the unit. 25

26 Annex Small glossary of technical terms Current consumption of 3-wire units Current rating/continuous Current rating/peak Leakage current of 2-wire units Minimum load current of 2-wire units Normally closed Normally open Operating voltage Power-on delay time The current consumption is the internal consumption of the proximity switch in the blocked state. When the output is blocked a very small leakage current of approx. 0.1 ma (open collector) flows through the output transistor. The continuous current rating indicates the current at which a proximity switch can be continuously operated. The peak current rating is the maximum current which may flow for a short time when power is applied without destroying the proximity switch. Especially DC units are rated in such a way that they can be charged with six times the nominal current for a short time because of the high inrush currents of many DC current loads (signal lamps, contactors...). The leakage current is the current that must flow through two-wire units in their open condition in order to supply the electronics with current. This leakage current also flows through the load. The minimum load current is the smallest current which must flow in the switched state to ensure reliable operation of the proximity switch. Principle of normally closed operation; if there is an object in the area of the active zone the output is blocked. Principle of normally open operation; if there is an object in the area of the active zone the output is switched. The nominal operating voltage is a value for which electrical equipment is rated. For proximity switches it is common to indicate an operating voltage range which determines an upper and a lower limit value. Within these limit values the function of the proximity switch is guaranteed. For DC units the residual ripple of the operating voltage must be included in these limits. If the residual ripple falls below the limit value of the operating voltage of the proximity switch, a smoothing capacitor must be used. A rule of thumb for this is: 1000 mf per 20 A current. The power-on delay time is the time which elapses between the application of the operating voltage and the readiness of the device to generate the correct switching signal. Within this time the internal voltage supply must be stabilised and e.g. in case of the inductive proximity switch the oscillator must start to oscillate. During this time (5 ms to more than 200ms depending on the type) the output is blocked by means of technical measures in the circuitry. º «¼»² ± ²¼ ¼ ¹²± ½»³ ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 26

27 Connection technology Programming Overload protection Reverse polarity protection Short-circuit protection Voltage drop (ON-state voltage) For some efector types the output function normally open or normally closed can be programmed. Depending on the type of efector the output function is programmed via a wire link, a connector or by selecting the pin connection. The output of a proximity switch is protected against overload if it can carry any current between nominal load current and short-circuit current continuously without damage. A switch is protected against reverse polarity if the wires of the proximity switch can be connected in any combination without the switch being damaged. As a rule 3-wire switches which are protected against reverse polarity must be short-circuit protected because otherwise reversing the output and the frame earth terminal (0 V) would lead to the destruction of the unit. The output of a proximity switch is short-circuit protected according to VDE 0160 if it withstands a short circuit of the load or a short circuit to ground at the output permanently without damage and if it is operational again without any switching operation being required after the short circuit has been removed. In the event of a short circuit the output transistor is blocked immediately. When the short circuit has been removed, the unit is immediately ready for operation again. Reversing the connecting wires does not lead to destruction of the units. Short-circuit proof units are at the same time protected against overload and reverse polarity. As the switching output of the proximity switch is equipped with a semiconductor switch (transistor, thyristor or triac), in the switched state a (small) drop in the voltage in series to the load occurs. In two-wire technology the voltage drop also serves to provide energy to the electronics of the proximity switch. The amount of the voltage drop depends on the type (for the IG-2005-ABOA e.g. it is 6.5 V at maximum load). 27

28 Index 2 2-wire units...8, 21, 22, wire units...10, 22, 23, wire... 10, 17 A AC...11 analogue... 4, 17 AS-i...18 automatic checking...13 B basic sensor...4 basics...7 binary...4, 7 built-in interface...18 C capacitive loads...15 common voltage...8 connected to a bus system...18 current... 8, 10, 17 current consumption...26 current output...17 current rating...26 D DC... 11, 12 derating...14 E electrical data...24 F FAQ...6 fluid...5 G guarantee...2 I incandescent lamps...25 inductive loads... 15, 25 information...2 inrush current...25 Intelligent...18 º «¼»² ± ²¼ ¼ ¹²± ½»³ L leakage current...8, 22, 26 level sensor... 5 load... 8 load capacity...12 M mechanical switch minimum load current N non polarised normally closed...16, 26 normally open...16, 26 O operating voltage operating voltage range...11, 19 output... 5 output function overload protection P parallel connection...22, 23 partially short-circuit protected polarity position... 5 power power supply...20 power-on delay time...21, 24, 26 programming protected against overload protective circuitry...12 Q quadronorm...9, 15, 16 R residual ripple...19, 26 resistance reverse polarity protection...14, 27 S sensor... 4 series connection...21, 22 short circuit short-circuit protection...12, 25, 27 smoothing capacitor standard sensors Supply supply voltage...17, 19 ± ±²»² ± ²¼ ±¾»½»½±¹² ±² ¾«ô ¼»² º ½ ±² ²¼ ½±² ±»³ 28

29 Connection technology T time characteristics...21 total harmonic distortion...20 tracing of errors...20 transmitters...17 U UC...11, 12 V voltage...8, 10, 17 voltage drop...10, 21, 27 voltage output