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
E-mail: wim@cardet.com
11.) Is the SWIM scale adequate for using in place of a static truck scale for buying and selling products by weight?
There are no WIM weigh-in-motion systems (manufactured by Cardinal Scale or anyone else) that are legal for trade in the US. Some states do use them for enforcement of legal weights, but even that is a gray area. As an industry, scale manufacturers are working on creating the NTEP requirements to someday allow a legal-for-trade WIM scale, but that could still be many years away from reality. While we are confident that our SWIM scale will produce consistent in-motion weights that are within 1-2% of actual static measurements, that is not accurate enough to legally exchange money for products sold by weight.
12.) What is the capacity of the SWIM scale?
Our SWIM is supported by four 50,000-lb load cells. This means that the SWIM could accurately measure a single axle up to 100 tons; however, the weighbridge itself is not rated for that amount of load. Based on the bridge capacity, you could safely weigh up to 80,000 lbs on any single axle. Because each axle is recorded independently and summed after the vehicle has passed, the total gross weight of the vehicle is unlimited. You could cross the scale with a five-axle truck with each axle weighing 80,000 lbs and the indicator would display a gross vehicle weight of 400,000 lbs. Or, hypothetically, you could cross the WIM bridge with a 100-axle truck and show a gross weight of 8 million pounds. This is an interesting aspect of the SWIM scale that isn’t possible in a typical static truck scale.
13.) What separates Cardinal Scale’s SWIM from the competitors?
Cardinal Scale’s SWIM is the only slow-speed weigh-in-motion truck scale using compression load cells. Because of the high resonance of this system, we see less spurious weight signals than our competitor’s shear beam cells. This makes filtering the samples easier and results in higher accuracy. Additionally, Cardinal Scale also manufactures our own load cells at the company’s factory in Webb City, MO, including the 50K-SCA stainless steel compression load cells used in the SWIM. Cardinal Scale is unique in the US scale manufacturing world in that we make our own load cells and tightly monitor our own manufacturing quality according to ISO and VCAP standards.
14.) How accurate is the SWIM scale?
The SWIM is designed to be used at speeds of less than 12 mph. The slower the vehicle speed the more accurate the measurement. The SWIM can also be used to weigh statically, and in static mode should meet or exceed NTEP tolerances (however, it would still not be legal for trade as it is not approved for this type use).
| SPEED | ACCURACY |
| Static | |
| (Static) 0 km/h (0 mph) | Gross wt. ±0.5% of applied |
| Dynamic | |
| 0-5 km/h (0-3 mph) | Gross wt. ±1.0% of applied |
| 5-10 km/h (3-6 mph) | Gross wt. ±1.5% of applied |
| 10-20 km/h (6-12 mph) | Gross wt. ±2.0% of applied |
15.) What are the site conditions that need to be met for a WIM scale to perform well?
To achieve the highest accuracy, the following conditions should be met:
a. The vehicle needs to approach and exit the scale in a straight line. Turning the vehicle during the weighment should be avoided. A straight approach and exit of 75 feet should be dictated.
b. All effort should be made to avoid conditions which would cause the vehicle to rock, sway, bounce, or have the suspension excited in any way. This requires pavement to be in good condition in advance and beyond the scale.
c. The vehicle should remain on a consistent grade during approach and exit of the scale. This does not mean it has to be level (up to 2% grade is acceptable), but all axles should remain on the same plane during the entire pass. We strongly recommend avoiding any change in the rising or falling of approaches for 75 feet on either side of the scale. This condition would shift the weight backward or forward onto axles unevenly during the pass.
16.) What is the footprint size of the SWIM scale?
The standard size SWIM model has a 12 ft long x 2.5 ft weighbridge to accommodate a standard 12-ft wide traffic lane width. The frame itself is longer because there are access plates on both ends to access the scale’s checking and SCA load cells. The overall exposed dimensions of the lower frame are 13 ft 9.25 inches x 3 ft 1.5 inches.
Cardinal Scale can manufacture the SWIM scale in various lengths if needed. Additional engineering costs will apply.
17.) What is the installation process?
The SWIM scale is installed by the user excavating a hole. After the pit is prepared, then the scale’s steel lower frame is suspended over the opening via Cardinal Scale-provided beams. The pit is then backfilled with concrete to encase the steel lower frame. After the concrete has cured, the support beams are removed and the load cells and weighbridge are lowered into place. Due to this type of installation, there is no separate pit coping. An installation/owner’s manual is available upon request. Also, if you go to www.wimscales.com you can see more 3D color renderings of the scale as well as a PowerPoint presentation.
18.) What is included with the standard system and what is the cost?
The SWIM listed in the Cardinal Scale price guide is a package deal for $19,599 list price. The SWIM as priced comes with the scale, loop detector and wire, indoor desk-mounted 825 weight indicator (with SWIM software loaded), and P600 ticket printer. If you purchase the standard package, then you will need a scale house or a weather-tight enclosure nearby to put the 825 indicator inside.
There is the option of purchasing an upgrade to get the SAT825 outdoor enclosure which is shown in the 3D rendering of the SWIM bulletin.
19.) This is a shallow scale pit. How are the electronics protected from water?
Because the SWIM pit is so shallow, the trim board is mounted above ground in a pole-mounted box or inside the scale house. If a SAT825 outdoor enclosure is purchased, then the trim board may also go inside of that above-ground enclosure. Typically, the loop detector is also mounted in the same enclosure. This prevents sensitive electronic equipment from being flooded if the pit drain fails. This also allows the scale technician to make adjustments while standing out of the traffic lane and without accessing the pit.
20.) How does the SWIM scale work?
By default, the SWIM is always ready to accept a vehicle for weighment. As soon as the first vehicle axle comes onto the scale, the 825 indicator begins sampling the load cells at a rate of 200 samples/second. The software watches the weight come up and then down as the axle exits. The sample is filtered to remove the rising and falling measurements from the sample as well as any spurious signals. Then it is averaged to determine the axle weight. That axle weight is then displayed as Axle 1 on the indicator and the system awaits the next axle. The SWIM must have a trigger to indicate that the end of the vehicle has passed so that 825 knows when to total the Gross vehicle weight. This is done by means of an inductive coil of wire placed in the pavement just after the scale. When the back bumper of the vehicle has passed the inductive loop, the system interprets that the weighment is over and displays the total of all axles, i.e the gross vehicle weight. The user can pre-set limits for single axles and/or gross weight. Over-weight readings will display in red. Weights within acceptable range will remain green.
21.) How does this scale ship?
The SWIM scale ships on a flatbed truck. It arrives assembled with load cells installed and the level beams on top all banded together. This skid with the scale measures 165 in x 36 in x 15 in. Additionally, there is a separate cardboard box with the indicator, checkrods, and printer. This box is 48 in x 40 in x 17 in. The total combined weight of both the skid and box is 4,331 lb shipping weight.
22.) Do you have more information, photos, or a training video I can view?
If you are not already familiar, Cardinal Scale has a dedicated WIM Web site: www.wimscales.com. This Web site covers all our WIM offerings, including the high-speed in-motion systems. You can go there online to view a PowerPoint presentation for the SWIM, view 3D renderings of the SWIM, see example views of the 825 SWIM weight display, and view peripheral device options.
Please give Cardinal Scale a call if you have any questions. We would be happy to discuss all your in-motion weighing options: (800) 441-4237 or cardinal@cardet.com.
23.) Are there additional peripheral devices I can add to the system to gather more information than just weight?
All WIM systems are available with a large number of options for peripheral devices: license plate reading cameras, overview cameras, traffic control devices, remote displays, RF readers, recording software, etc. The best plan for figuring out what you need is to describe to our sales staff the sequence of events you envision for your WIM system and then they will help with a suggested layout of products. We also have short WIM questionnaire we can share with you if you would like a tool for describing your needs.