FAQ - Frequently Asked Questions
Here you will find the answers to your most frequently asked questions.
Web Tension
How is web tension measured?
The web tension is measured indirectly via an idler roller over which the web is guided. The tension of the web creates a load on the roller. This load can be measured by two force sensors (load cells) on each side of the idler roller.
What is the unit of web tension?
Web tension is nothing other than a tensile force. The SI unit for force is Newton N (metric), or Pound-force lbf (imperial). A typical unit, independent of the material width is N/m or lbf/in.
What is the torque of web tension?
Web tension and torque are linked by a mathematical formula. Torque = web tension x radius of a roll. If I want to keep the web tension constant, simple rules apply: If the diameter of the rewinder increases, I need increasing torque on the rewind shaft; if the diameter of the unwinder decreases, the torque of the unwind shaft decreases.
Force Sensors
What is a force sensor?
Force sensors are used to measure compression, force, strain and load. Many have internal strain gauges bonded to the metal structure which react to even the smallest deformation causing a change in resistance and giving feedback on these results. Force sensor is an alternative term, depending on the design and application they may also be called load cell, force transducer or force measuring bearing.
Where are force sensors used?
One of the most common uses is for tension control applications. Web type material is fed over an idler roller. Force sensors on each end of this roller detect the force that acts on the roller generated by the material tension. The feedback signal from the force sensors is processed and delivers a direct indication of the strain or tension in the material in Newtons, kilograms, grams or pounds. Applications for wire tension control apply a pulley/sheave and a single force sensor instead of the roller with two force sensors.
What is the difference between dead shaft and live rollers?
Dead shaft rollers are usually made of two separate parts. The non-rotating axis and the roller sleeve are connected via bearings. This allows the sleeve to rotate around the axis. In contrast, live shaft rollers are made from one piece. Bearings sit in each force sensor on either end of the roller. Dedicated types of force sensors are available for both types of rollers.
What is the nominal force of a force sensor / load cell?
The required nominal force FNom of a force sensor must be calculated individually per application. It determines the maximum force that a sensor can measure. Higher loads on the force sensors by web tension and the weight of the idler roller result in higher FNom. For applications where you use two force sensors on each end of an idler roller (typically for web tension measurement) the maximum load is divided by two, as the force is distributed evenly to the left and right. For FMS force sensors, the FNom is always specified in direction of the Red Point as this marking defines the measuring direction with positive sensor signal. The following information is essential for the calculation of FNom:
- entry and exit angle of the web (wrap angle) in relation to the horizontal ((to obtain a reference to the weight force)
- web tension (typically min. and max. values)
- weight of the idler roller.
For easy and quick estimation of the required FNom, FMS offers a free online tool – the FMS Calculator
How does the nominal force affect the measuring range of a force sensor / load cell?
Many specifications of a force sensor refer to its nominal force FNom. This also applies to the measuring range. The measuring range is made up of the upper and lower values. The upper value is the nominal force, the lower value is calculated from the quotient of FNom. Typical specifications for the measuring range of FMS force sensors are 1:30 or 1:100. The following example shows the calculation of a LMGZ-series sensor with a FNom of 1´000 N. The measuring range always refers to the entire measuring range. In case of web tension measurement with two force sensors on an idler roller, the measuring range refers the mean value of both force sensors.
What is the accuracy class of an FMS force sensor / load cell?
FMS defines the accuracy as a function of the nominal force FNom of the respective force sensor and refer to this as the accuracy class. The accuracy class is made is made up of linearity error, hysteresis, and total error. All three influencing factors are verified during the final inspection of a force sensor before shipping. The accuracy class applies in the entire measuring range of the force sensor.
FMS-Calculator
What is FMS-Calculator?
FMS-Calculator is a browser-based program for sizing and selection of FMS force sensors.
Are there restrictions in the FMS-Calculator?
There are many factors you need to consider during the design phase. In addition to supposedly fixed specifications such as environmental influences and installation space, there are also other, often not yet defined boundary conditions that may change in the course of a project. To take these into account, we recommend that you discuss your designs with us. Our specialists can help you even if the application specifications may not lead to a clear result.
Which languages are supported by FMS-Calculator?
FMS-Calculator supports German and English. You can select the language as well as your preferred units in the settings.
Can I save calculations in the FMS-Calculator?
Yes, you can save any calculation. Create a project or add your calculation to an existing project and you can access it again at any time.
Can I exchange calculations with other users?
Projects and corresponding calculations can be shared with other Calculator users. On the project administration mask, you can add the email-address of the users you want to add to the project. Feel free to also add your FMS sales representative to get support with your calculation.
How can I size double-range force measuring of the LMGZD series?
Enter the maximum AND minimum material tension. Go to the Optimization step and select a dual-range force sensor of the LMGZD series. Select the size and nominal force and check in the force diagram (on theleft) whether the force sensor is suitable or not.
How are the results displayed in the FMS-Calculator?
After successful sizing completion, you can output the result as a file in a pdf format. The file is ideal for your internal documentation or further optimization.
What are the system requirements for the FMS-Calculator?
A computer with web browser and internet access.
Measuring Amplifiers
What are the advantages of ethernet communication over power outputs on a measuring amplifier?
The resolution of sensitive force sensors and amplifiers can be used much better using a 16 bit word instead an analogue signal (with a measuring range of 1:50 the signal is as small as 20 mV at lowest measurable point). Wiring of machines can be reduced a lot, and especially modular machines are much easier to connect from module to module.
What’s the difference between analogue and digital measuring amplifiers?
Analogue amplifiers use many more components that are temperature dependent, the worst being the potentiometers to adjust offset and gain. Signal filtering depends on capacitors that will lose their capacity over time. In digital amplifiers all parameters are stored reproducibly in a memory facilitating a replacement without recalibration.
Segmented Tension Roller
What is the FMS-segFORCE?
The FMS-segFORCE segmented tension roller is a new, advanced device designed to monitor web tension more accurately then conventional tension monitoring. It features multiple independent force sensors along the roller to provide detailed tension profiles.
What is the difference between conventional tension monitoring vs the FMS-segFORCE?
A roller with a set of standard loadcell can only measure the average tension across the width. Using a double-channel amplifier one can detect higher or lower tension on left or right side. With the FMS-segFORCE one gets a tension profile with up to 50 measuring points across the width of the web material. The resolution of the profile can be set by selecting appropriate segment width and quantity.
Where is the FMS-segFORCE applied?
One main application is in the quality control of web material. The tension profile can be used to identify defective material and exclude it from further processing steps. The causes can be determined and corrected before valuable machine hours are lost. The tension of the individual slit strips can also be measured in secondary slitter / rewinders. Deviations are directly indicated, and suitable countermeasures can be taken.
