Inductive sensors Enhanced Durability for the Deep-Freeze Industry

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FAULHABER Drive Systems

Wuxi InfiMotion Technology Co., Ltd.

Inductive sensors are particularly suitable for use in harsh industrial environments. However, permanently low temperatures can cause extreme damage to standard sensors over time, which increases the failure rates and very quickly separates the wheat from the chaff among the possible alternatives.

On a production area of around 5,000 square meters, a company specializing in frozen baked goods primarily produces pretzels and various types of bread rolls. The dough is produced on site and the baked goods are either ready-baked, pre-baked or deep-frozen as dough pieces and then stored for dispatch.

Preservation of around 15,000 baked goods per hour

The baked goods are preserved in a system with two blast freezers. Each blast freezer consists of five cooling towers, each with a paternoster system. The trays with the baked goods are transported through this cooling section, which has a constant temperature of -24° C (-11.2°F).

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"The individual towers with the paternosters are used to achieve the time required for deep-freezing, with each tray taking around 40 minutes for a complete system cycle. Each blast freezer offers space for around 140 trays for deep-freezing in a continuous process. This means, for example, that up to 7,500 pasta products can be preserved per hour with just one cooling section," explains the company's technical manager.

Position sensing ensures smooth sheet transfer

A plate chain system is located around the system, on which the trays with the baked goods are placed in order to automatically load the blast freezers. Once a tray has passed through a cooling tower via the paternoster, it is transferred to the next tower via a chain conveyor. For this purpose, one chain of the conveyor has a carrier that positions the tray accordingly. The carrier position is monitored by an inductive sensor. "If we didn't monitor the position, the carrier could jam the sheet metal and block its onward transportation to the next tower," says the technical manager.

For this reason, a sensor is installed at each transfer station to the individual towers and at the inlet of the first tower and the outlet of the last tower, so that a total of six sensors are in operation. If a sensor detects a carrier, the drive of the carrier chain is de-energized and the motor brake is activated so that the chain is at the desired end position for transferring the sheet to the next tower.

System downtimes due to frequent sensor failures

The inductive sensors previously used in the blast freezers were part of the original standard system equipment and consisted of commercially available devices with an operating temperature range of -25° C to +70° C (-13°F to 158°F) . However, these sensors could not withstand constant low temperatures along the cooling section over the long term. However, these sensors could not withstand the constantly low temperatures along the cooling section in the long term and therefore failed almost regularly. In this case, the PLC stopped the chain conveyor and the entire system was at a standstill until the defective sensor was replaced. According to the technical manager, this ended up happening every three weeks on average, which meant that the system was down regularly. As sensor solutions from IPF were already being used elsewhere in the plant, the technical manager asked the sensor specialist for an alternative to the vulnerable devices."

Solution specialist for extended ambient temperatures

The inquiry ultimately proved to be the right decision, as IPF is one of the leading suppliers in the field of inductive sensor technology with a comprehensive portfolio of more than 750 devices in various designs and sizes and with standard and extended switching distances. In addition, IPF is a specialist for solutions that have to be designed for extended ambient temperatures. This includes the IA30012W with M12 connector in a robust metal housing (protection class IP67) with integrated amplifier, which ultimately proved to be the ideal solution for the application at the manufacturer of frozen baked goods with an operating temperature range of -40° C to +100° C (-40°F to 212°F) and a range of up to 10 mm.

Sustainably increased availability of blast freezers

The technical manager recalls the first experiences: "In 2017, we initially installed two new sensors in a cooling section in order to test the devices extensively. As these sensors no longer failed, a year later we retrofitted the entire system with both cooling sections with the solutions from IPF."

According to the technical manager, downtimes have improved significantly since then. "Whereas previously we were confronted with the need to replace defective sensors within just a few weeks, we are now talking about years. Of course, sensors still fail from time to time. But not due to the low temperatures, but due to unintentional mechanical damage, and therefore no longer with the frequency that was the case with the old devices. With the inductive sensors from IPF, we have been able to significantly reduce system failures and sustainably increase the availability of the blast chillers."