Proximity Switches Get With the Program

You will also be able to be much more flexible in the design of your machine. Sensors can be programmed either at the sensor or externally on the PLCs. The tolerance of the teached switching point on a programmable sensor is much better than a nonprogrammable sensor (less than 5%). The reason for this is that the customer programs the sensor at a certain target distance. In general, a nonprogrammable sensor has a tolerance of +/-10% of the sensing distance. Upgrading from a standard to a programmable proximity sensor would be well worth it.

Alex Gasser
Business Development Manager
Baumer

You’re All Setpoint

While it is not clear which characteristics of the proximity switch need to be fine-tuned, some capacitive and inductive (eddy-current) devices do offer a level of programmability. Some sensors offer an adjustable setpoint. The setpoint determines the nearness of the object required to activate the proximity switch. Depending on the sensor, this adjustment may be made with a screw adjustment, a push button or remotely from a PLC or other controller output. If the sensing application requires more than simple presence/absence but requires an adjustable setpoint, these sensors are a good solution. The typical setup sequence involves positioning a target at the location where the proximity switch is to trigger and adjusting the sensor to trigger at that point.
While these sensors do cost more, if the alternative requires a large stock of different sensors and the labor to change them for different runs, then the programmable sensors can pay for themselves.

Don Martin
President
Lion Precision

Proximity switches can be used for detecting metal slide carriers at the production line.

Remove the Mask

The machine builder’s description does not reveal the underlying reasons for needing to fine-tune the switch characteristics with a frequency that necessitates doing it via software. It could be production runs of materials of different metallic composition, inconsistent formulation, vibration in the line or compensation for temperature changes, flexibility and ease of operation, to name a few.

The trade-off here goes beyond choosing a programmable proximity switch that costs 4 or more times the cost of a standard proximity switch. It also adds an engineering labor component to the process—fine-tuning via software—that further increases customers’ cost of operating the machines. It is worthwhile to test one of the programmable proximity sensors to see if it actually improves efficiency, accuracy and quality in production enough to offset the increased hardware and labor costs. The choice also ties the machine builder to a single vendor that can add a potential for line shutdown if the specialized parts are not readily available. In today’s competitive marketplace, where reliable standard proximity sensors are widely available from a range of suppliers, most machine builders are looking to decrease the cost of their control solution and not lock in their customers to a single part number or supplier.

Certainly, there are applications that call for the flexibility and adaptability offered by a programmable proximity switch, but those are often niche applications that require increased precision or fine positioning not offered by a standard proximity switch. Is the fine-tuning requirement masking what is actually the need for an edge control or measurement type of solution? These types of applications often require an analog output in addition to a discrete output. In these cases, the increased performance, quality and throughput delivered by the machine or system employing programmable or measuring proximity switches justifies the increased cost and convenience. The machine builder will want to make sure the system is easy to maintain for the customer to keep the cost of ownership down.

Gilbert Guajardo
Product Marketing Manager for Proximity Sensors
Omron Electronics

Stay Off the Field

It makes sense to fine-tune sensors based on application requirements via software. There are two things that users should focus on.

1. Fine-tuned sensors can increase productivity and efficiency, while decreasing the failures.
2. Setting up fewer part numbers in the parts pool can reduce the inventory cost and makes it easier to select a sensor.

There are two ways we can do this: the method that Sick recommends and the method that it does not recommend.

Sick does not recommend having a field-programmable sensor programmed in the field via software by the user.
Why don’t we recommend this method?

1. Cost of setting up sensors: Each sensor needs to be programmed to a specific parameter by the user. The technicians need to be trained to use the programming tool. This increases the cost of installation.
2. Cost of sensor: Field-programmable sensors are more costly than standard inductive sensors. The market pricing of field-programmable sensors is substantially higher than a proximity sensor that can do the job.
3. Cost of repair:  During the time it takes to find the right technician and the right programming tools and to figure out the right parameter settings for the sensor, you lose very valuable machine time, man time and material while paying more money for the sensor.