IO-Link: End to Analog Sensors

With most sensors now coming out with an IO-Link output, could this mean the end of using traditional analog sensors? IO-Link is the first IO technology standard (IEC 61131-9) for communications between sensors and actuators on the lower component level.

Analog sensors

A typical analog sensor detects an external parameter, such as pressure, sound or temperature, and provides an analog voltage or current output that is proportional to its measurement. The output values are then sent out of the measuring sensor to an analog card, which reads in the samples of the measurements and converts them to a digital binary representation which a PLC/controller can use. At both ends of the conversion, on the sensor side and the analog card side, however, the quality of the transmitted value can be affected. Unfortunately, noise and electrical interferences can affect the analog signals coming out of the sensor, degrading it over the long cable run. The longer the cable, the more prone to interference on the signal. Therefore, it’s always recommended to use shielded cables between the output of the analog sensor to the analog card for the conversion. The cable must be properly shielded and grounded, so no ground loops get induced.

Also, keep in mind the resolution on the analog card. The resolution is the number of bits the card uses to digitalize the analog samples it’s getting from the sensor. There are different analog cards that provide 10-, 12-, 14-, and 16-bit value representations of the analog signal. The more digital bits represented, the more precise the measurement value.

IO-Link sensor—less interference, less expensive and more diagnostic data

With IO-Link as the sensor output, the digital conversion happens at the sensor level, before transmission. The measured signal gets fed into the onboard IO-Link chipset on the sensor where it is converted to a digital output. The digital output signal is then sent via IO-Link directly to a gateway, with an IO-Link master chipset ready to receive the data. This is done using a standard, unshielded sensor cable, which is less expensive than equivalent shielded cables. And, now the resolution of the sensor is no longer dependent on the analog card. Since the conversion to digital happens on the sensor itself, the actual engineering units of the measured value is sent directly to the IO-Link master chipset of the gateway where it can be read directly from the PLC/controller.

Plus, any parameters and diagnostics information from the sensor can also be sent along that same IO-Link signal.

So, while analog sensors will never completely disappear on older networks, IO-Link provides good reasons for their use in newer networks and machines.

To learn about the variety of IO-Link measurement sensors available, read the Automation Insights post about ways measurement sensors solve common application challenges. For more information about IO-Link and measurement sensors, visit www.balluff.com.

Sensing Types of Capacitive Sensors

Similar to inductive sensors, capacitive sensors are available in two basic versions.  The first type is the flush or shielded or embeddable version however with capacitive sensors they are sometimes referred to as object detection sensors.  The second type is the non-flush or non-shielded or non-embeddable version however again with capacitive sensors they are sometimes referred to as level detection sensors.

CapacitiveTypes1

The flush or object detection capacitive sensors are shielded and employ a straight line electrostatic field.  This focused field is emitted only from the front face of the sensor allowing the sensor to be mounted in material so that only the face of the sensor is visible.

The highly focused electrostatic field is perfect for detecting small amounts of material or material with low dielectric constant.  The typical range of a flush 18mm capacitive sensor is approximately 2 to 8mm depending on the objects dielectric constant.  As with any capacitive sensor the sensor should be adjusted after installation.

CapacitiveTypes2

If the sensors are mounted adjacent to each other the minimum gap should be equal to the diameter or the adjusted sensing distance whichever is less.  These sensors can also be mounted opposing each other however the distance should four times the diameter of the adjusted sensing distance whichever is less.

CapacitiveTypes3Shielded or flush capacitive sensors are perfect for detecting solids or liquids through non-metallic container walls up to 4mm thick.  If you are detecting liquid levels through a sight glass with the sight glass mounting bracket then the flush mounted sensor is the preferred choice.

CapacitiveTypes4The non-flush or level detection capacitive sensors are not shielded and employ a spherical electrostatic field.  This field is emitted from the front face of the sensor and wraps around to the sides of the sensor head.  Unlike the flush sensor this version cannot be mounted in material where only the face of the sensor is visible.  Non-flush sensors have better characteristics and better performance in applications with adhering media.

CapacitiveTypes5The spherical electrostatic field provides a larger active surface and is perfect for detecting bulk material and liquid either directly or indirectly.  The typical range of a flush 18mm capacitive sensor is approximately 2 to 15mm depending on the objects dielectric constant.  As with any capacitive sensor the sensor should be adjusted after installation.

CapacitiveTypes6If the sensors are mounted adjacent to each other the minimum gap should be equal to three times the diameter or the adjusted sensing distance whichever is less.  These sensors can also be mounted opposing each other however the distance should four times the diameter of the adjusted sensing distance whichever is less.

Shielded or flush capacitive sensors are perfect for detecting solids or liquids through non-metallic container walls up to 4mm thick.  If you are detecting liquid levels through a sight glass with the sight glass mounting bracket then the flush mounted sensor is the preferred choice.

Capacitive sensors are perfect for short range detection of virtually any object regardless of color, texture, and material.

To learn more about capacitive sensors visit www.balluff.com.

Flush or Non-Flush – What’s the Difference?

In a previous blog Flush or Non-Flush, Looks Can Be Deceiving, Jeff mentions the two common housing designs of inductive sensors, flush and non-flush. So what does this mean to you when you are applying an inductive or even a capacitive sensor?

Flush-style sensors actually have a shield that restricts the magnetic field so that it only radiates out of the face of the sensor. Flush-style, or shielded sensors, can be mounted flush in a metal bracket or even in your machine without the metal causing the sensor to false trigger. When mounting two shielded inductive proximity sensors next to each other, you should typically leave one diameter of the sensor between adjacent sensors. The shielded-style of sensor will typically have approximately one-half of the sensing distance that a non-shielded version will have. For example, a 12mm shielded inductive sensor will have a sensing distance 2mm whereas a non-shielded version will have a sensing distance of 4mm. Although shielded style sensors have a shorter sensing range they can be buried in a machine or a bracket that will offer protection against damage.

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