What are the different types of outputs for sensors?
All sensors have one or more (types of) outputs. An output generally sends the currently known measured value of the sensor. What that signal looks like depends on the output type. What is the difference between all these outputs and when is which output type used? This article explains the most common forms.
Sensors can have many different types of outputs. The possible outputs of a sensors detemine in which applications the sensor can be used. Vice versa, the same can be said: the type of application detemines which sensor you need.
In this article we discuss the different possible outputs. how these work and for which use cases these can be applied.
Digital vs. Analog
First, we make a distinction between two types of outputs: an analog and a digital output. A sensor with a digital output signals a logical value. In other words: Yes or No, 0 or 1, True or False, Valid or Invalid . A digital output is very well-suited to indicate the presence of an object (at a certain distance) or detecting whether a set limit value has been reached. Does the sensor "see" the object or not? Is the value reached or not? During a detection or non-detection the logical value changes from a 0 to a 1, or vice versa! Examples of digital (switching) outputs are PNP/NPN, relay, solid state relay and PushPull.
A sensor with an analog output is capable of giving a signal that is continuously partallel to the measured value. An analog signal is a signal that can register values without intervals. Think of a constantly fluctuating temperature in an outdoor location, such as the conveyor belts in the production of steel beams: the analog output changes parallel en mostly linear with the change of the measurement of the sensor. Another example is the change of a distance from 0 to 1.000 cm or a temperature drops from 200°C to 20°C. Examples of analog outputs are 0-10 Vdc, 4-20 mA, 0-5 Vdc or 0-20 mA.
Types of digital outputs: PNP or NPN
Sensors with a PNP or NPN switching contact make use of a transistor output. The type of transistor output determines whether the sensor switches PNP or NPN. Sensors with a PNP or NPN switching output are equipped with at least three wires; A " + " (Pin 1 / brown wire), a " – " (Pin 3 / blue wire) and a switching wire (Pin 4 / black wire).
PNP switching output
NPN switching output
PushPull switching output
Solid State Relay (SSR) output
Normally Open, Normally Closed or Antivalent output
All sensors with a digital switching contact, whether it is a PNP/NPN, solid state or PushPull contact have the ability to switch Normally Open (NO) or Normally Closed (NC). In some cases the sensors only switch NO or NC. If a sensor is capable of switching NO as well as NC it is called antivalent.