Sensing Linear Position in a Telescoping Hydraulic Cylinder
Whether it is raising the bed of a dump truck or a riser tensioner cylinder used on an offshore oil rig, telescoping hydraulic cylinders play a vital role. These cylinders are designed to offer long stroke lengths where the total length required would not fit into the machine. Moreover, telescoping cylinders are multi-stage and they are manufactured for accurate and reliable position sensing, especially in harsh environments.
In telescoping cylinders the stroke must typically be known before the sensor can be made. Moreover, in-cylinder installation generally requires gun-drilling the piston to mount a magnet, which is difficult and adds to the final cost of the cylinder. And the inbuilt cylinder can make LDT’s susceptible to damage from radial shock, heat and excessive vibration.
Telescoping Hydraulics Require a Different Sensor Approach
Enter the SL Series Linear Position Sensors offered at Control Products Inc. The sensor technology is the combination of a few well-known components of linear position sensors put together and manufactured in a new way. The sensor design uses draw-wire technology coupled with a sealed LVDT to deliver an absolute positioning system that is easily mounted internal to the cylinder and highly resistant to shock, vibration and EMI.
For instance, the SL1300 is a new kind of sensor that satisfies telescoping cylinder requirements with a maximum stroke length of 23 feet. The transducer for the 1300 consists of a spring-loaded spool inside a housing and cable. One end of the cable is attached to the moving piston, and the other end wraps around the spool. As a cylinder’s piston changes position, the draw-wire wraps or unwraps around the spring-loaded spool. The inside diameter of the spool is threaded, and the outside diameter of an LVDT has mating threads. Rotational motion of the spool is thus translated into the linear motion of the LVDT, which produces a signal that is a function of absolute piston position.
One of the biggest advantages of the SL Series Sensor is that it is capable of measuring any stroke length over its sensing range with almost no modification to an existing design, most notably without core drilling of the rod. This makes position sensing more practical in long stroke applications especially telescoping cylinders.
About Linear Position Sensors Made By Control Products Inc.
In 2001, CPI introduced its first generation of SL series LVDT based linear position sensors. Its latest offering is a family of sensors that uses the same cable and LVDT technology but the spool and LVDT housing can be mounted outside the cylinder, so no end cap machining is necessary. Instead, the cable attached to the piston is fed through a hydraulic hose that threads into the end cap of the cylinder. The other end of the hose is fitted to a steel enclosure that houses the spool and LVDT assembly.
This setup provides easy installation because all that’s needed is to attach the cable to the cylinder’s piston, thread one hose end into an 18 mm or #8 SAE port in the cylinder, then mount the housing to machine framework of the cylinder itself.
The transducer available in four models to accommodate cylinder strokes up to 120 in. The four models are SL0390, SL1200, SL0391 and SL1201, where SL0390 and SL1200 have high shock and vibration resistance and measure strokes to 40 and 120 inches, respectively. And, the SL0391 and SL1201 are intended as drop-in replacements for in-cylinder mounted magnetostrictive LDTs and measure strokes to 40 and 120 in. The sensor can be operated with any standard signal conditioner, with 0- to 5-Vdc, 0- to 10-Vdc, and 4- to 20-mA outputs and 10 to 30 Vdc input being most common.
To learn more about Linear Position Sensors, visit http://www.cpi-nj.com/
In telescoping cylinders the stroke must typically be known before the sensor can be made. Moreover, in-cylinder installation generally requires gun-drilling the piston to mount a magnet, which is difficult and adds to the final cost of the cylinder. And the inbuilt cylinder can make LDT’s susceptible to damage from radial shock, heat and excessive vibration.
Telescoping Hydraulics Require a Different Sensor Approach
Enter the SL Series Linear Position Sensors offered at Control Products Inc. The sensor technology is the combination of a few well-known components of linear position sensors put together and manufactured in a new way. The sensor design uses draw-wire technology coupled with a sealed LVDT to deliver an absolute positioning system that is easily mounted internal to the cylinder and highly resistant to shock, vibration and EMI.
For instance, the SL1300 is a new kind of sensor that satisfies telescoping cylinder requirements with a maximum stroke length of 23 feet. The transducer for the 1300 consists of a spring-loaded spool inside a housing and cable. One end of the cable is attached to the moving piston, and the other end wraps around the spool. As a cylinder’s piston changes position, the draw-wire wraps or unwraps around the spring-loaded spool. The inside diameter of the spool is threaded, and the outside diameter of an LVDT has mating threads. Rotational motion of the spool is thus translated into the linear motion of the LVDT, which produces a signal that is a function of absolute piston position.
One of the biggest advantages of the SL Series Sensor is that it is capable of measuring any stroke length over its sensing range with almost no modification to an existing design, most notably without core drilling of the rod. This makes position sensing more practical in long stroke applications especially telescoping cylinders.
About Linear Position Sensors Made By Control Products Inc.
In 2001, CPI introduced its first generation of SL series LVDT based linear position sensors. Its latest offering is a family of sensors that uses the same cable and LVDT technology but the spool and LVDT housing can be mounted outside the cylinder, so no end cap machining is necessary. Instead, the cable attached to the piston is fed through a hydraulic hose that threads into the end cap of the cylinder. The other end of the hose is fitted to a steel enclosure that houses the spool and LVDT assembly.
This setup provides easy installation because all that’s needed is to attach the cable to the cylinder’s piston, thread one hose end into an 18 mm or #8 SAE port in the cylinder, then mount the housing to machine framework of the cylinder itself.
The transducer available in four models to accommodate cylinder strokes up to 120 in. The four models are SL0390, SL1200, SL0391 and SL1201, where SL0390 and SL1200 have high shock and vibration resistance and measure strokes to 40 and 120 inches, respectively. And, the SL0391 and SL1201 are intended as drop-in replacements for in-cylinder mounted magnetostrictive LDTs and measure strokes to 40 and 120 in. The sensor can be operated with any standard signal conditioner, with 0- to 5-Vdc, 0- to 10-Vdc, and 4- to 20-mA outputs and 10 to 30 Vdc input being most common.
To learn more about Linear Position Sensors, visit http://www.cpi-nj.com/
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