In this paper, we show how to navigate through some important specifications in a typical data sheet of a three-wire induction sensor. Let’s also look at two data sheets of three-wire induction sensor information from 2 different vendors, Pepperl + Fuchs and Schneider Electric, and discuss the common specifications.
3-wire induction proximity sensor
Before we get into the 2 proximity sensor data datasheets, let’s quickly look at what a three-wire induction sensor is, discuss the different types of output, and the schematic symbol of a 3-wire inductive proximity sensor. A three-wire induction sensor is an electronic device that can detect Fe (Fe) targets without any physical contact. An internal electronic switch works when it detects the target. Because the sensor is an electronic device, it requires a DC power supply.
Today, induction proximity sensors are used in the industry to replace devices such as mechanical switches. There are two different types of NPN and PNP three-wire induction sensors.
IEC induction sensor symbol
The symbol that best represents the induction sensor was developed by the International Electrotechnical Commission (IEC).
There are a number of shapes inside the symbol that represent the three-wire induction sensor:
– Diamond indicates a proximity sensor
– Fe indicates that it is an induction sensor
– The transistor indicates that it is an NPN output type
– The switch usually indicates that the internal electronic switch closes when the sensor detects the proximity of a target
Three-wire induction sensor data sheet
Now we have to look at the 2 data sheets of the proximity sensor of 3 ordinary wires.
Output type specifications
Let’s discuss the specifications of the output type. The output type can be PNP or NPN, which determines how the load is connected to the sensor. Although both can look the same, they are not interchangeable.
Current or switching capacity
Current current or switching capacity in mA is another specification discussed. Unlike mechanical limit switches or other similar devices, the proximity sensor can transmit only a small current before being damaged. The maximum allowable current for these sensors is 200 mA.
Operating voltage or power supply voltage limit
An important characteristic is the operating voltage or voltage range of the power supply. As previously described, a three-wire induction sensor is an electronic device that requires a DC power supply. Sensor data sheets always provide a wide range of power supply voltages in which the sensor operates as designed.
Switching function or discrete output function
Let’s look at the switching feature or discrete output function. Just like any switch, proximity sensors can have normally open (NO) or normally closed (NC) contacts. This data sheet indicates the status of the switch before it is activated.
Voltage drop or maximum voltage drop
Another important characteristic is the voltage drop or maximum voltage drop. Many of us think that a closed switch drops to zero volts when it is closed. In most cases this is true. Unfortunately, this is not the case in the world of electronic proximity sensors.
This data sheet specification shows how much voltage can be reduced when the proximity switch is closed. This may or may not be a problem, but be aware that voltage drops do occur.
Another feature to consider is the Switching Frequency. Whenever the target approaches the proximity sensor, the internal switch works and generates a voltage pulse.
Can a proximity sensor be used to measure speed?
It is not intended for this purpose but may be slow. Each time a gear passes through the sensor, a voltage pulse is generated. The speed or rpm of the gear is determined by converting the pulse capture frequency. The proximity sensor has switching frequency characteristics that limit its use for speed measurement. Speed sensors are designed to act exactly as proximity sensors.
Operating distance or nominal sensor distance
An important feature is the operating distance or nominal sensor distance. Simply put, distance is the ideal condition in which the sensor can detect the target and operate its internal switch successfully. Keep in mind that this specification does not take into account external conditions such as voltage and temperature source.
Change status or LED
Status Let’s talk about a specification called the Switching State Indicator or Status LED. Almost every vendor has an LED indicator as part of the physical body of the proximity sensor. The purpose of the LED is to indicate when the proximity sensor is activated.
Be careful that the LED lights up even if the load is connected incorrectly.
In the review, it is better to say that vendors use slightly different names for the proximity sensor specifications in the data sheets. Fortunately, similarities help us determine the important values needed to use and troubleshoot them correctly.
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