Control components are often designed with redundancy in mind to ensure safety or increased availability. This means that the sensors used to measure a parameter must also be designed and installed with redundancy in mind. In the following article, you’ll learn how to integrate three position sensors into a cylinder with minimal effort.
The piston movement of a hydraulic cylinder is continuously measured so that the control system can track the position of the element being moved by the cylinder at all times. In hydraulic engineering, for example, lock gates are opened and closed using hydraulic cylinders. To monitor and control the gates from the control room, their position must be continuously tracked. Magnetostrictive sensors are used to measure the piston movement of a cylinder. Such a sensor is integrated into a hydraulic cylinder and continuously records the position of the piston rod. A rigid, pressure-resistant rod is inserted into the deep bore of the piston rod, while the sensor electronics are located at the bottom of the cylinder outside the cylinder.
According to the Gertman Federal Institute of Hydraulic Engineering, approximately 30 percent of locks in the field of hydraulic engineering are over 100 years old. Such structures require repair or replacement. In many cases, redundant measurement systems are used to meet the requirements of the Machinery Directive 2006/42/EC. This means that the integrated sensors must also be designed redundantly.
To redundantly measure the piston movement of a hydraulic cylinder, the Temposonics G-Series GT3 magnetostrictive sensor can be used. This sensor incorporates three independent sensors (units) in a single housing. In the event of a replacement, the entire sensor must be removed. It is not possible to replace just one of the three units within the sensor. Additionally, a significant amount of space is required behind the cylinder: the rigid sensor rod is as long as the piston stroke. To remove the sensor from the cylinder and install a replacement sensor, space equivalent to a full piston stroke is required behind the cylinder.
With the goal of optimizing sensor replacement in confined spaces, Temposonics developed a redundant measurement system consisting of three individual position sensors. To integrate three separate sensors into a cylinder with limited space, they must be converged as if in a funnel. This requires sensors whose measuring rods can be bent, such as the Temposonics R-Series V RFV sensor.
Due to the flexibility of their measuring rods, these sensors allow for an arrangement. A holder or sensor carrier is used to mount the three RFV sensors and brings the flexible measuring rods of the sensors together. The three measuring rods are guided through the cylinder in a common pressure-resistant sensor tube. This design offers two key advantages:
Hydrosaar implemented this solution to set up a redundant measurement system in a hydraulic cylinder for two locks on the Main River. The existing hydraulic cylinders used to move the lock gates were modified and equipped with three individual RFV sensors housed in a sensor tube. To this end, the following modifications were made to the existing cylinders:
The H3 sensor tube from Temposonics was used to house the three RFV sensors in the cylinder. The bracket developed by Hydrosaar is designed to accommodate and align the three RFV sensors. This bracket allows for easy insertion of the measuring rods and ensures a secure hold even when the cylinder is vibrating.
The housing protects the three sensor electronics located outside the cylinder from debris in the event of flooding. A distinctive feature of this housing is its two-part design. The sensor carrier separates the upper part from the lower section and serves to hold the sensors. To connect the cables to the sensors, simply remove the cover. The lower part of the housing contains the junction of the three RFV sensors. Both parts of the housing can be removed separately or as a single unit. Due to the housing’s low weight of less than 4 kg, it can be held with one hand by an employee during both installation and removal. The unique feature of the flexible measuring rods offers an enormous advantage during on-site installation or removal: due to the flexibility of the measuring rods, the housing with the sensors can be tilted sideways and removed or installed. This requires only about 500 mm of space behind the cylinder.
This design offers the advantage of allowing sensors to be replaced individually. Thanks to the modular housing, a sensor at a lock can be removed and reinstalled on-site in about 30 minutes. This represents a significant time savings compared to the effort required when the cylinder must be removed to replace a sensor. This implementation demonstrates that it is possible to integrate three individual magnetostrictive position sensors into a single tube within a cylinder with minimal effort: Simple with triple!
A magnetostrictive position sensor is integrated into a hydraulic cylinder by inserting the sensor rod into the drilled-out piston rod. The cylinder is sealed via the flange to prevent any hydraulic fluid from leaking out. The position magnet, which marks the position to be detected, is mounted at the bottom of the piston rod and moves with the piston rod. This position is continuously detected and output by the sensor electronics.