Difference between NPN and PNP output types of proximity switch sensors and their corresponding wiring methods

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This post was last edited by Wang Tianze on 2015-9-29 at 22:21. As a new member of the “Haichuan Forum,” I’ve noticed over the past couple of days that many forum members have been asking questions and discussing how to wire proximity switches and photoelectric sensors, as well as how to determine whether they are active or passive types. Some people also aren’t clear about the wiring methods for connecting loads. Here, we would like to share our experience from DOKAI Technology to help analyze and discuss these issues. If there are any shortcomings, feel free to contact us directly. There are differences between the NPN and PNP output types of proximity switches, as well as corresponding wiring methods. Among various types of proximity switches, aside from two-wire switches, it is necessary to consider the way in which the sensor connects to the system (PLC) both during design selection and during installation. In most proximity switch output circuits, whether they are of the NPN or PNP type, the output is of the open-collector type (with the AC type being an exception). These circuits have three basic signal lines, namely (VCC ； GND ； OUT), and there is also a 4-wire OUT (NO+NC). I. Definition elements of NPN and PNP output lines First, let’s explain the definitions or names of these 3 signal lines: 1. VCC: This refers to the power supply, also known as +V ； (Commonly known as the positive terminal of the power supply; connected to the red or brown wire). 2. GND: refers to the ground wire, also known as 0V ； (Commonly known as the negative terminal of the power supply, connected to the blue wire). 3. OUT: This refers to the signal output line, also known as the load ； (Connect to the black (or white) wire). Simply put, the meanings of NPN and PNP types are as follows: NPN type: can also be referred to as type N, where N indicates that the signal terminal outputs a negative voltage ； The internal switch is connected to the signal terminal and the negative pole. PNP type: Can be abbreviated as P type, where P indicates that the signal terminal outputs a positive voltage ； The internal switch is connected to the signal terminal and the positive pole. Meanwhile, both types come in NO (normally open) or NC (normally closed) variants, with different default output states; therefore, choosing solely between NPN or PNP output types does not provide a complete description when making a selection. From the perspective of the signal terminal, NPN or PNP types should strictly speaking be as follows: http://down1.hcbbs.com/album/201509/25/133841qzxfx2d1fed2wdpx.jpg. However, in practical applications, it is not sufficient to simply know the output type at the signal terminal in order to determine whether the wiring methods for proximity switches, photoelectric switches, sensors, etc. are correct; it is also necessary to understand the input and output signals as well as the power supply required for the specific application. As a professional sensor manufacturer, Duokai Technology has found through years of working with clients that, in practice, sensors can be connected either directly to relay devices or to microcontrollers, or they can also be connected to PLCs. Depending on the method of connection, the wiring for the signal lines varies accordingly; the various applications are summarized below. II. Wiring methods for proximity switches and photoelectric switches: A proximity switch is a type of sensor, and its connection methods are not limited to just one; the most common configuration is the three-wire type ； The two-wire configuration is relatively simple, while the other four-wire connection method also arose as a necessity based on the three-wire system. Overall types are as follows: 1. Two-wire sensors: 1-1, NO (normally open); 1-2, NC (normally closed). Note: Two-wire sensors can be AC (alternating current) or DC (direct current). 2. Three-wire sensors: 2-1, NPN – NO (normally open); 2-2, NPN – NC (normally closed); 2-3, PNP – NO (normally open); 2-4, PNP – NC (normally closed). 3. Four-wire sensors: 3-1, NPN (NO + NC), i.e., normally open + normally closed type; 3-2, PNP (NO + NC), i.e., normally open + normally closed type. 4. Wiring diagrams: http://down1.hcbbs.com/album/201509/25/133927nq7losul5ua7oooi.jpg http://down1.hcbbs.com/forum/201509/22/170051wlbg4lhybbkqwo2a.jpg. 4-1. Operation of NPN-type sensors: NPN-type proximity switches use a common positive terminal (COM). The internal switch in such sensors connects the signal output line OUT to the GND (0V) terminal, which results in a low-level signal output from OUT. NPN – NO normally open type: In the absence of a signal trigger, that is, when the signal output line OUT is disconnected from the GND (0V) negative terminal of the power supply, it is as if the OUT signal output is at a high level ； When a signal is triggered, the signal output line OUT is connected to the GND (0V) power supply’s “–” terminal, resulting in a low voltage of 0V being output. NPN—NC normally closed type: When there is no signal to trigger it, the output takes a low voltage level of 0V, which is the same as GND; in other words, the signal output line OUT is connected to the GND (0V) terminal ； When a signal is triggered, the signal output line OUT is disconnected from the GND (0V) power supply’s “–” terminal, which means the OUT signal output is effectively open. 4-2, PNP operating mode: In a PNP proximity switch, the negative terminal is common (COM); the internal switch connects the signal line OUT to the positive pole of the VCC (+V) power supply, which means that the OUT signal output terminal outputs a high-level voltage. PNP—NO normally open type: This is the state of a proximity switch when there is no signal trigger, that is, when the signal output line OUT is disconnected from the positive terminal of the VCC (+V) power supply; in this case, the OUT signal output is considered to be at a low level ； When a signal is triggered, the output takes on the same voltage as the \"+\\" terminal of the VCC (+V) power supply; in other words, the signal output line OUT is connected to the \"+\\" terminal of VCC (+V), resulting in a high-level output. PNP—NC normally closed type: When there is no signal to trigger it, the output of this proximity switch has the same voltage as the \"+\\" terminal of the VCC (+V) power supply; in other words, the signal output line OUT is connected to the \"+\\" terminal of VCC (+V), resulting in a high-level output ； When a signal is triggered, the signal output line OUT is disconnected from the ‘+’ pole of the VCC (+V) power supply, which means the OUT signal output is effectively at a high level. For the 4-wire NPN—NO normally open + NC normally closed types 4LR12-P5N and 4LR18-L6N, as well as the PNP—NO normally open + NC normally closed types 4LR12-L3P and 4LR18-P9P, an additional output wire OUT is provided on top of the three-wire configuration; users can choose to install and connect it according to their needs. 4-3: Connected via PLC or relays, the PLC can be connected to either the positive terminal VCC or the negative terminal GND of the power supply, with COM ports being of the single-point common type; the input types include active and drain types. The source type input is of the NPN type: when a signal is present, current is supplied from the PLC to the sensor. Either an external power supply is used to provide the input signal, or the power supplied by the PLC itself is utilized for the input circuit; all input signals are \"active\" signals, and they are connected to the PLC’s inputs in an independent manner. The leaky input type is PNP: when the sensor generates a signal, current is output to the PLC. In this configuration, the PLC provides the input signal source, and all input signals are gathered at the common connection point COM; this type of input is also known as a junction input ； Generally, for Japanese PLCs* that use a common positive terminal (COM) the most, an NPN proximity switch is required. European and American series PLCs* typically have a common cathode, requiring PNP-type proximity switches. With the continuous advancement of automation, single-ended common-emitter (S/S) versions are now available to meet the requirements of different applications. When the S/S terminal on the PLC serves as the common terminal for the power supply of the input signals to the PLC, this terminal must be connected to the positive pole of the power supply; in such a case, an NPN type proximity switch is required. Conversely, if this terminal must be connected to the negative pole of the power supply, then a PNP type proximity switch is needed. Note: The two major PLC manufacturers, Siemens and the Japanese-based Mitsubishi, have opposite definitions for source-type and sink-type, which can easily lead to confusion and incorrect judgments when using or understanding these concepts. Among sensor manufacturers, DOKAI, Shenzhen Duokai Technology Co., Ltd., specializes in the production of inductive proximity switches and photoelectric sensors; the stability of its product quality is highly reliable. At the same time, we can customize professional proximity sensors and other products with different specifications, voltages, and performance requirements for you. DOKAI Technology adheres to the principle of specialization, aiming to provide users with efficient, stable, and reliable products. The product types are classified by specifications into ultra-short, ultra-small, extended, general-purpose, round, square, and U (groove) shapes. Classified by wiring method: two-wire, three-wire, four-wire, aviation plug type, and terminal direct connection type. Classified by voltage: DC direct current output type, AC alternating current output type. Classified by performance: economy version, high-end version. Models such as 3LR5-L08N1, 3LR12-P5N1, 3LR12-P5P1, 3LS8-W2N1, 3LS10-W5N1, 3LS17-W6N1, 3LS18-Q6N1, 3LR6-L1N1, 3LR8-P2N1, 3LR6.5-P2N1, 3LS17-Q6P1, 3LR4-L08N1, C4L12-P5N, P3LR12-P5N1, and so on. In terms of performance, these products are of high quality and can serve as substitutes for imported products; they feature comprehensive protection functions. They are comparable to a wide range of products from renowned imported brands such as AUTONICS, OMRON, PANASONIC, KEYENCE, BALLUFF, P+F, SICK, and Schneider.