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My Old Industrial Sensor has 4 Pins

Posted by Tracy Molnar on Thu, Oct 17, 2013

…and the replacement only has 3 – can I still use it?

It’s always a good idea to double-check that a different-looking industrial sensor will work as a replacement for your currently-installed part, because looks can be deceiving.  Take for example the question above regarding the number of pins in a sensor’s connector. 

Connecting industrial sensors

I hear this question a lot, and usually just have to ask a few of my own to get the answer.

Check the data sheets!

There are three things you need to know to determine if you can use an industrial sensor with a different number of pins in the connector as a drop-in replacement:

  1. Do  the connectors on both sensors have the same basic configuration?
  2. Will the new sensor give you the output you require?
  3. Is the output on the same pin as the old sensor?

All three questions can be answered after a quick comparison of sensor data sheets, with particular attention focused on the wiring diagrams and connector pinouts.

Connector configurations

First, make sure the connector thread matches up. This information should be stated on the data sheets under “Mechanical specifications – Connection type.”  An example is M12 x 1.

Mechanical specifications

Next, look at the physical connectors as well as the pinout diagrams.  Do the key(s) and pin placement match up?  Even if there are fewer pins, are the ones that are present located in the same positions on the connector?  A common example of this examination is shown below.  The three M12 connectors on the left have different numbers of pins, but the same general configuration.  The two M8 connectors on the right have a different number of pins, but also a different pin placement configuration.

Pinout diagram

It’s worth noting that sometimes a pin will be physically present in a connector, but not have any internal connection to the sensor electronics.  If a pin number is not shown in the wiring diagram on the sensor data sheet, then it doesn’t matter if the corresponding actual pin is there or not.

Industrial sensor pinouts

Output types

Compare the output descriptions on the two data sheets.  Are they the same?  Outputs can take many forms – just a few common examples are 3-wire PNP normally open, 2-wire normally closed, and 4-wire NPN (two outputs – one normally open and the other normally closed).  The actual wiring of the sensor to be replaced should also be checked – just because a sensor has two outputs doesn’t mean both are being used.  If your current sensor is a 4-wire type, you may only have the normally open output connected.

Sensor output types

Wiring diagrams and pinout

The final thing to look at is the pin numbers listed on the wiring diagram.  If you’re using the normally open output of a 4-wire NPN sensor, and that output is on pin 4 of the M12 connector, then even if the replacement sensor has a 3-wire configuration with only normally open output, as long as that output is also on pin 4 of the M12 connector, the new sensor will work as a drop-in replacement.  If the output you need from the new sensor is on a different pin than you’re currently using, but the basic connector configurations match, you may still be able to use the replacement sensor. As long as the cordset has a conductor on the new output pin and you’re able to rewire the connection to the control circuit, the replacement sensor will work.

Wiring diagrams


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Topics: Inductive Sensors, Cables/ Cordsets, Capacitive Sensors, Ultrasonic Sensors, Photoelectric Sensors, Ask an Expert, Magnetic Sensors

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