{"id":14735,"date":"2025-04-15T08:28:00","date_gmt":"2025-04-15T13:28:00","guid":{"rendered":"https:\/\/blog.misumiusa.com\/?p=14735"},"modified":"2025-04-15T14:51:46","modified_gmt":"2025-04-15T19:51:46","slug":"npn-and-pnp-io-module-terminology","status":"publish","type":"post","link":"https:\/\/us.misumi-ec.com\/blog\/npn-and-pnp-io-module-terminology\/","title":{"rendered":"NPN and PNP: IO Module Terminology"},"content":{"rendered":"\n
\"\"<\/a><\/figure><\/div>\n\n\n\n

NPN and PNP are terms used to classify transistors and their mode of operation. These terms are often also used to classify PLC I\/O modules, as well as their associated devices. It is important to understand this classification, as it can affect component compatibility and setup within a PLC system<\/a>.<\/p>\n\n\n\n

Despite being an essential factor to consider when choosing PLC components, manufacturers are not always clear about how their product is classified. Adding to the confusion is the terminology used; NPN-type modules are often referred to as \u201csinking\u201d or \u201cactive-high,\u201d while PNP-type ones are often called \u201csourcing\u201d or \u201cactive-low.\u201d<\/p>\n\n\n\n

In this article, we\u2019ll discuss what these terms mean, as well as what to look for when purchasing I\/O devices for your next PLC system.<\/p>\n\n\n\n

Basic Explanation<\/h2>\n\n\n\n

In general, sinking and sourcing refer to the positioning of a given device relative to the power supply and ground\/common line. The following concepts are best explained by examining the flow of current within a DC (direct current) circuit. Please keep in mind that I will be using conventional current notation, where current flows from positive (higher voltage) to negative (lower voltage).<\/p>\n\n\n\n

<\/p>\n\n\n\n

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Mitsubishi Electric PLC Input\/Output Unit, iQ-R Series<\/a><\/figcaption><\/figure><\/div>\n\n\n\n

The circuit on the top shows an input module connected to a 24Vdc power supply and switch. The input module has an uninterrupted connection to the positive end of the power supply, referred to as the common line.<\/p>\n\n\n\n

When the switch is closed, the electrical current will flow from the power supply\u2019s positive terminal, through the closed switch, and into the input module before returning to the power supply\u2019s negative terminal via the common line. This current flow is represented on the circuit with the black arrow.<\/p>\n\n\n\n

You can think of the closed circuit as a river with current flowing from upstream to downstream. The input module would be considered sinking as it is the closest device \u201cdownstream,\u201d while the switch would be considered sourcing as it is the furthest \u201cupstream.\u201d<\/p>\n\n\n\n

In electrical terms, the input module will only activate when it detects a positive voltage signal at the input, in this case +24Vdc. This is where the term \u201cactive high\u201d stems from, as the module activates when the voltage at the input end is higher than the voltage on the common line.<\/p>\n\n\n\n

Now let us look at the other circuit. This circuit uses the same elements as the one above, except that the switch is now located near the negative terminal of the power supply. As a result, the common line now rests at the positive terminal of the power supply. Closing the switch in this circuit now connects the input module to the negative terminal, completing the circuit and allowing current to flow through the module in the same direction as the previous circuit. <\/p>\n\n\n\n

In this case, the input module would be considered \u201csourcing,\u201d while the switch would be considered \u201csinking.\u201d In other words, it will only activate when the voltage at the input end is lower than the voltage on the common line\u2014hence the term \u201cactive low.\u201d<\/p>\n\n\n\n

These terms also carry over to output modules, and the idea is the same: sinking output modules will share a common line with the negative end of the power supply, while sourcing output modules share their common line with the positive end.<\/p>\n\n\n\n

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Product: <\/strong>Mitsubishi Electric Automation: PLC Output Unit, L Series<\/a><\/figcaption><\/figure><\/div>\n\n\n\n

One final thing to note: <\/strong>These terms do not apply to modules that use alternating current for logic signals. As the voltage waveform changes polarity, the direction of the current within the circuit will reverse, meaning that would-be sinking devices become sourcing and vice versa.<\/p>\n\n\n\n

What should I use?<\/h2>\n\n\n\n

By now you probably have a robust idea of the differences between NPN and PNP I\/O modules. The question now is picking the right one for your PLC system.<\/p>\n\n\n\n

One of the main deciders is the polarity of the logic signal. Say that you decide to configure your system to run on positive logic, wherein a positive voltage signal will trigger a component to energize.<\/p>\n\n\n\n

In this case, it may be ideal to go with a sinking NPN input module and sourcing PNP output module, as both modules are designed for positive logic signals. Conversely, many power supplies can be configured for negative logic; these systems would benefit from a sourcing PNP input module and a sinking NPN output module. (It is possible to have both positive and negative logic within a system, but I would strongly recommend against this.)<\/p>\n\n\n\n

Keep in mind that NPN and PNP configurations also apply to I\/O devices like sensors and switches, so if you\u2019re looking for a drop-in replacement for an I\/O module, you may need to check those devices as well. When in doubt, always refer to the device\u2019s datasheet.<\/p>\n\n\n\n

It\u2019s worth noting that some I\/O modules are not limited to either a PNP or NPN configuration. Some modules, like the QX70 from Mitsubishi<\/a>, have compatibility for either positive or negative logic. Modules like these are excellent for when you\u2019d like to have guaranteed compatibility with both NPN and PNP devices.<\/p>\n\n\n\n

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Mitsubishi Electric PLC
Input Unit, DC Sensor, MELSEC-Q Series<\/a>
<\/figcaption><\/figure><\/div>\n\n\n\n

Conclusion<\/h2>\n\n\n\n

Hopefully this information has proved useful for helping you understand what sinking and sourcing mean and how they apply to your PLC system. Knowing the difference can save you from a ton of headaches when building your next control cabinet.<\/p>\n\n\n\n

Be sure to check out MISUMI\u2019s inventory of I\/O modules. <\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

Explore the difference between NPN and PNP modules and learn what \u201csinking\u201d and \u201csourcing\u201d mean to avoid costly PLC setup mistakes.<\/p>\n","protected":false},"author":85,"featured_media":14780,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"om_disable_all_campaigns":false},"categories":[1137,6],"tags":[],"aioseo_notices":[],"gutentor_comment":0,"_links":{"self":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/14735"}],"collection":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/users\/85"}],"replies":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/comments?post=14735"}],"version-history":[{"count":4,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/14735\/revisions"}],"predecessor-version":[{"id":14804,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/posts\/14735\/revisions\/14804"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media\/14780"}],"wp:attachment":[{"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/media?parent=14735"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/categories?post=14735"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/us.misumi-ec.com\/blog\/wp-json\/wp\/v2\/tags?post=14735"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}