How Do I Choose The Right Sensor?

All applications have certain specific needs, but, in general, the following steps will help you choose the correct sensor for your application:

Step 1:

What is the sensing distance required?


The sensing distance is the distance between the tip of the sensor and the object to be sensed. The selection guide and the specifications table for each sensor family regardless of the manufacturer will list the sensing distances.

SICK IME12-08NPSZC0S Inductive Proximity Sensors

Some things to keep in mind are:


(A.) In many applications, it is beneficial to place the sensor as far as possible from the sensing object due to temperature concerns. If a sensor is placed too close to a hot temperature source, the sensor will fail quicker and require more maintenance.


Greater distance may be achieved with extended and triple range sensors. In many applications, a sensor may not be mountable close to the sensed object. In this case, longer sensing distances are needed. Certain sensor product lines offer extended sensing distance sensors from 8mm to 30mm, and triple sensing distance sensors in 8mm and 12mm
round formats.


In many cases, using an extended distance sensor to get the sensor farther away from
the detected object can be beneficial to the life of the sensor. For example, without an extended distance sensor you may not be able to place the sensor close enough to the detectable object, or you may need to buy more expensive high temperature sensors.


Another example would be a mechanical overshoot situation, where mounting the
sensor farther from the detection object may eliminate unneeded contact with the
sensor, thereby extending the life of the sensor.


These are just a few examples, but the benefits of using extended distance sensors are obvious in many applications. Think of how extended distance sensors could save you time and money in your application.


(B.) The material being sensed (i.e. brass, copper, aluminum, steel, etc.) makes a difference in the type of sensor needed.

Note: If you are sensing a non-metallic object, you must use a capacitive sensor. Many materials are more difficult to sense and require a shorter distance from the sensor tip to the object sensed.


If sensing a material that is difficult to sense, you may consider using a unique stainless steel sensing technology. This will measure virtually all materials at the specified sensing distances.

Step 2:


How much space is available for mounting the sensor?


Have you ever tried using a round sensor or short body versions, and not been able to make it fit? The rectangular sensors can meet your needs. The same technology used in a standard round proximity sensor is enclosed in a rectangular housing. This technology includes sensing distances, electrical protection and switching frequencies similar to round sensors.

Telemecanique XS8C4A4PCP20 Proximity Sensor

Step 3:


Is a shielded or unshielded sensor needed?


Shielded and unshielded sensors are also referred to as embeddable and nonembeddable. Unshielded sensors allow longer sensing distances but shielded sensors allow flush mounting.

Step 4:


Consider environmental placement concerns. Will the sensor be placed underwater, in a high-temperature environment, continually splashed with oil, etc.?

This will determine the type of sensor you may use. In the selection tables and in the specification tables for each sensor family, the manufacturer lists the environmental
protection degree ratings. Most of the sensors are rated IEC-IP67 and others are
rated IP65 or IP68.


These ratings are defined as:


IP65: Protection from live or moving parts, dust, and protection from water jets from any direction.


IP67: Protection from live or moving parts, dust, and protection from immersion in water.


IP68: Protection from live or moving parts, dust, and protection from submersion in water under pressure.

Step 5:


What is the sensor output connected to?


Note: If using AC sensors, please skip this step.


The type of output required must be determined (i.e., NPN, PNP or analog). Most PLC products will accept either output. If connecting to a solid state relay, a PNP output is needed.


Step 6a:


Do I need 2, 3, or 4-wire discrete outputs?


This is somewhat determined by what the sensor will be connected to. Some simple guidelines to use are:

TypeGuidelines
  2-wireWill work with sinking or sourcing devices.Only 2 wires to terminate. Higher leakage current.
  3-wireMost popular output. Familiar to most users. (Must select between NPN and PNP outputs.)
  4-wireAllows configurability in one device. May have both NPN/PNP selection or NO/NC selection. Allows user to stock one part for numerous applications.
Omron E2E-X2F1-M1 Inductive Proximity Sensors

Step 6b:


Do I need analog outputs?


This is determined by the sensor application and what the sensor will be connected to. Devices with analog outputs produce an analog output signal approximately proportional to the target distance.

tsensors.qxd

TypeGuidelines
1-5mAavailable on analog inductive sensors
4-20mAavailable on analog inductive sensors
0-5VDCavailable on analog inductive sensors
0-10VDCavailable on analog inductive sensors and ultrasonic sensors

Step 7:


Determine output connection type.


Do you want an axial cable factory attached to the sensor (pigtail) or a quick disconnect
cable?


There are many advantages to using a quick-disconnect cable, such as easier maintenance and replacement. All proximity sensors will fail in time and using a Q/D (quick disconnect) cable allows for simple replacement.


Factory attached axial cables come in a pre-determined 2m length. Q/D cables come in 2m, 5m, and 7m lengths. Extension cables are available in 1m and 3m lengths to extend the length
of the standard Q/D cables.


Q/D cables are offered in PVC and PUR jackets for meeting the requirements of all applications. Axial cables typically come with a PVC jacket. PVC is a general purpose insulation while PUR provides excellent oxidation, oil and ozone resistance. PUR is beneficial if the cable is exposed to oils or placed in direct sunlight.


There are also advantages to a factory attached axial cable:


Cost: The cable is integrated into the sensor and included in the price. Q/D
cables must be purchased separately.


Environmental impact: Since the cable is sealed into the sensor, there is less chance of oil, water or dust penetration into the sensor, which could cause failure.

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