Automation Canada - Cables & Connectors Issue - 4

HOW TO CHOOSE A SENSOR CABLE
CONNECTIVITY CORNER BROUGHT TO YOU BY MURR CANADA
BY COLIN CARTWRIGHT
When I started as a controls engineer more than 30 years ago,
choosing a sensor cable was relatively easy because there weren't very
many options to choose from. It was 1990 and if a sensor had a
connector (many were still widely available with screw terminals at that
time), it was either a 7/8 Mini connector or a M12 connector. The
smaller M8 style connector had only just been released so sensor
manufacturers had not really adopted it yet.
Back then, choosing a sensor cable basically came down to four
things: the connector type (7/8 or M12), the connector style (straight or
right angle), the number of poles/pins (3 or 4) and the length of the
cable. Double-ended cables were available, but as we were usually
terminating everything back at the main panel, we rarely used them.
Oh, I nearly forgot - you could choose any colour or jacket material as
long as it was yellow PVC!
These days, you'll struggle to find a sensor with a 7/8 " connector, but
M12 and M8 connectors have truly stood the test of time. They are
definitely the most common connectors found on sensors today. Now
connectors haven't changed much, but there has been a huge advance
in the types of material available to make sensor cable jackets, so we are
no longer stuck with a yellow PVC jacket as our only choice. We'll dig
into this little more later.
Having selected sensor cables for thousands of automation projects
over the years I wanted to share some of the things I always consider
when choosing a sensor cable.
Let's start off with the sensor connector itself. Most sensors have M12
or M8 male connectors with 3 or 4 poles/pins, so choosing the sensor
end of the cable is quite simple. Once you've determined the connector
type and pin configuration, the only other thing you need consider is
the orientation of the cable relative to the sensor. You can choose
straight or right-angle depending on whether you want your cable to
C A N A D I A N A U TO M AT I O N

run inline or perpendicular to the sensor.
You can skip this next step if you only require a single-ended sensor
cable, but if you plan on connecting your sensor to an IP67 I/O module
you will need a double-ended cable, so you will need to know the size
and type of the ports on the I/O module. An I/O module with M12
female ports is simple because the pin configuration/layout is same for
M12 male connectors no matter if they have 3 or 4 pins. However, pay
more attention to IP67 I/O modules with M8 female ports because the
pin configuration on 3-pole and 4-pole M8 male connectors are
different. You cannot plug a M8 male 3-pin connector into a M8 female
4-pole port, or vice-versa. If you ever do run into a situation where your
I/O module has M8 ports with 3 poles and you have sensor with a M8
4-pole connector, you'll need to use a field-connector or a Y-cable to
connect to two ports.
VOLUME 3, ISSUE 2

4
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Automation Canada - Cables & Connectors Issue

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