Force motor scales, also called magnetic force restoration or MFR scales, are used when precise, high resolution measurements need to be taken. The resolution of a scale is the number of decimal places the scale can accurately produce. Scientific labs and paint mixers are just two examples of industries that would require this kind of precision. Often, high resolutions are necessary to ensure the consistency of a product.
How Force Motor Scales Work
While there are slight variations to the design based on the manufacturer, force motor scales typically use a simple lever and fulcrum. Attached to one end of the lever is the weighing platform, where you’d place your sample. On the other end is a force coil suspended in a magnetic field (if you know anything about speakers, it’s similar to the way they operate). A displacement detector and power amplifier produce a current that holds the lever balanced in the null position while weight is applied to the platform. The amount of current necessary is directly proportional to the weight on the pan. A microprocessor is usually used to monitor the current that is produced in response to the applied weight and sent the information to the scale’s indicator.
The Drawbacks of Force Motor Technology
While this design does provide the necessary precision and resolution for sensitive operation, there are a few drawbacks. The first and probably biggest for consumers is simply the cost. Just purchasing a force motor scale is expensive. However, even after purchase, a force motor scale requires more resources to operate effectively.
Because the accuracy characteristics of a force motor scale change with time, as well as with changes in temperature, vibration, and air currents, they are susceptible to error. To reduce this type of error, many of these scales are constructed with an internal calibration mass as well as a method for applying this mass to the sensor. However, to achieve accurate results, the scale must be recalibrated fairly often. A calibration mass device adds additional costs to an already expensive scale.
Another major drawback is that force motor scales are only good for very low capacity loads, as they become impractical at higher capacities. Large amounts of electrical current would be required to support a heavier load, which means a bigger current draw and higher self generated heat, and therefore inaccuracy. Either that or even more expensive and complicated systems would need to be implemented use mechanical advantage to reduce the load seen by the force motor.
For many purchasing managers, the cost of force motor scales is simply not equal to the benefits such a scale would provide and so they settle for a strain gage scale. Other businesses simply suffer through costs that seem inevitable.
But what if we told you there was a better, less expensive option?
The Cost Effective Alternative
An Arlyn Ultra Precision scale is an industrial grade scale that utilizes Surface Acoustic Wave (SAW) technology scale to produce inherently accurate, high-resolution measurements. An internationally patented technology, we’ve been able to incorporate it into our scales in such a way that we’re able to take advantage of a spring element load cell without the disadvantages typically found in strain gage load cells.
Why SAW Technology is Better
Unlike strain gage load cells, which measure stress or strain and are subject to plastic deformation, SAW load cells feature two transducers that are attached to either side of the spring element. Because SAW load cells are not dependent on stress applied to the spring element, we’re able to reduce the amount required by at least 90%! This means an inherently stronger and more accurate load cell that is less subject to deformation and distortion.
One of the transducers acts a transmitter and the other a receiver. The transmitter sends a bulk wave to the receiver, where it is picked up, sent through an amplifier, amplified, and sent back to the transmitter, where the process begins again.
Because the distance between the transducers is known, we also know how much time it takes for the wave to be sent between them. When a load is placed on the platform, the distance between the transducers changes, which ultimately changes the frequency of the bulk wave being passed between them. Because the measurements being taken are time measurements, we are able to eliminate the need for an analog to digital conversion, which means they are automatically in digital format and the scales are inherently more accurate.
Ultimately load cell errors are reduced to a high degree with this technology, which cannot be said for force motor technology. Measurements are also less subject to distortion from changes in temperature and air currents. Measurements do not pull extra electrical current, and are far less costly than the initial purchase of a force motor scale.
Our Ultra Precision scales are in a price range comparable to high end strain gage scales offered by other well known industrial scale companies but are ten to twenty times more accurate. They are generally less than one third the cost of a force motor scale and provide precision and accuracy that is at least as good as that of force motor technology, if not better.
Available Capacities and Resolutions
The lowest capacity Ultra Precision scale we offer is ten pounds, which features an extremely high resolution of one ten-thousandth of a pound (.0001). Our highest capacity scale is 500 pounds with a resolution of five thousandths of a pound (.005). The middling sizes have the following capacities and resolutions:
- 25 lb x .0002 lb
- 50 lb x .0005 lb
- 100 lb x .001 lb
- 200 lb x .002 lb
- 300 lb x .002 lb
Contact Arlyn Scales
Whether you just have questions you’d like us to answer or would like help selecting the scale that best meets your needs, we’re here to help!
And Don’t forget to ask about our customization options. We’re a factory direct manufacturer, which means we can help you with anything you need. From computer connectivity and data transfer to set point controllers and software we’ve got you covered. Contact us today!