1.) How accurate are your QWIM series of in-motion vehicle scale?
When properly installed in an acceptable site, both the Model QWIM-1 and QWIM-2 meet or exceed the tolerances for a Type III in-motion scale as defined in ASTM E1318. This means that for a suitable sample of vehicles, two standard deviation or about 96% of the sample, will have gross weight errors of less than or equal to +/-6%, groups of two or more axle errors of less than or equal to +/-10% and single axle errors of less than or equal to +/-15%. Speed and axle spacing accuracies are +/- 1 mph and +/- 0.5 ft respectively.
2.) What do you mean by a “suitable sample of vehicles”?
When determining the accuracy of a weigh-in-motion vehicle scale, those vehicles with highly sprung or unstable loads like tank trucks without internal baffles or automobile haulers should be excluded from the sample set because of the inaccuracies introduced by their unstable loads.
3.) What is meant by “an acceptable site”?
ASTM 1318 describes the requirements for an acceptable site for a weigh-in-motion vehicle scale. These requirements include horizontal and longitudinal alignment, slope, cross slope, smoothness and lane width and markings. All of these characteristics help minimize any inconsistencies in the weight signal as the vehicle moves across the sensor array.
4.) I thought you could attain better accuracy from an in-motion scale. Why are the errors so large?
Actually the errors are not that large for an in-motion scale that can weigh vehicles at speeds up to 80 mph. You also have to understand what the errors listed above mean. The error distribution is generally in a bell-shaped curve. Two standard deviation or 95.5% of the sample will have a gross or total weight error somewhere between -6% and +6%. Based on the relationships under the empirical rule, it follows that one standard deviation or 68.3% of the sample will have gross weight errors between -3% and +3%. When you consider this, the typical error of an in-motion scale is significantly less than the ASTM 1318-based error.
5.) What can be done to improve the accuracy of in-motion vehicle scales?
Of course, the most obvious things are to ensure that the scale is properly installed in a site meeting the scale manufacturer’s criteria. If your scale is located adjacent to a weigh station with a full length static vehicle scale, you may wish to install an auto-calibration system that will automatically adjust the in-motion scale’s calibration to meet the calibration of the static scale based on a sample of weights from both scales. This all takes place in the background and is completely transparent. Auto calibration systems reduce the average error in the in-motion scale by 50% or more but you must maintain the static scale calibration to achieve this level of improvement.
6.) How long does it take to install a QWIM Series of in-motion scale?
There are a number of factors that influence installation time but, if the site is properly prepared ahead of time, installation can be completed in as little as six to eight hours. Properly prepared means that all of the roadside conduit and pull boxes have been installed leaving only the installation of the quartz sensors and inductive loop.
7.) Can I perform the installation myself?
The short answer is no. Installation of the Kistler LINEAS® quartz sensors require that you be certified by Kistler to perform the installation. The Kistler warranty is void if the sensors are installed by personnel who are not Kistler-certified.
8.) What advantages do quartz sensors have over other types of in-motion weighing technology?
Quartz sensors offer a number of advantages over other in-motion technologies. Some of them are:
- Quartz sensors are sanded smooth with the surrounding pavement making them immune to damage from passing snowplows.
- Quartz sensors require very little maintenance. Unlike load cell and bending plate technologies, quartz sensors only require a periodic visual inspection to ensure that the epoxy holding them in place remains in good condition. Bending plate and load cell-based in-motion scales are subject to corrosion and require that their restraint system be properly adjusted.
- Quartz sensors can be installed quickly. Load cell and bending plate technologies require construction of a concrete foundation in the roadway along with a drain system to prevent the accumulation of water. Installation of these in-motion scales often require several days of construction while quartz sensors are typically installed in small cutouts in the pavement.
- Unlike piezoelectric BL sensors, quartz sensors are not sensitive to changes in pavement temperature.
- Quartz sensors do not use strain gauges like load cell and bending plate technologies and are therefore resistant to voltage surges that would otherwise destroy a strain gauge.
9.) Several companies offer quartz-based in-motion scales. Why should I buy from Cardinal?
There are many reasons why you should consider purchasing your quartz-based in-motion scale from Cardinal. Here’s just a few:
- Cardinal is a family owned US company located in the heart of the US making it easy to access scale sites coast to coast.
- Cardinal has been building and installing quartz-based in-motion scales for over sixteen years and has been in the scale business for over fifty years. We’re here to stay.
- Cardinal is vertically integrated manufacturing the in-motion system including not only the roadside instrumentation cabinet but the WIM controller and software as well. This means you have single source responsibility.
- Cardinal maintains its own WIM service vehicles that not only bring the scale to your site but the equipment needed to install it as well.
- Cardinal’s professional staff of hardware and software engineers offer turn-key solutions to your most complex requirements.
- Cardinal offers the complete solution. In-motion vehicle scales are only a small part of the services and products offered by Cardinal. From pit and low-profile heavy duty static vehicle scales using either strain gauge or hydraulic load cells to state-of-the-art weighing instrumentation, Cardinal has the solution. Our long history of supplying weighing systems for state highway weigh stations has enabled us to provide the most cost effective solution for your project.
- Cardinal’s network of independent professional scale dealers ensures that on-site service is just a phone call away.
10.) I still have some questions. What do I do next?
Simple. Either call, fax or e-mail us for a quick response.
Telephone: (417) 673-4631
Fax: (417) 673-5001