If you've just purchased a Spee-Dee checkweigher or inherited one that requires a performance update or recalibration, you're in the right place. After years of helping customers optimize their systems, I've seen the same checkweigher setup mistakes repeated over and over. The good news? Once you understand how the key settings work together, you can achieve excellent package-to-package checkweigher accuracy in about 30 minutes.
The most common problem I encounter when it comes to accurate checkweighing is customers struggling with repeatability. They run the same package or container over the checkweigher multiple times and get wildly different readings. This inconsistency makes it impossible to trust your system or maintain quality control.
Here's what you should expect: when you run the same container across your checkweigher repeatedly, the standard deviation should be less than 0.5 grams. That's not a hard rule for every application, but it's a practical target that indicates your system is properly tuned.
To hit this target, you need to understand four critical settings and how they interact with each other.
This one is straightforward. Measure your bag or container and enter the length into the system’s HMI. No confusion here, and customers rarely get this wrong.
2. Container-to-Photo-Eye Distance
This setting is extremely important and often misunderstood. It's the key to accurate weighing.
Here's how it works: when the trailing edge of your package passes the photo-eye, the system starts a timer. Using that timer and the known belt speed, the checkweigher calculates how far the package has traveled down the line. This calculation tells the system exactly when the package is fully positioned on the weigh cell and ready for weighing.
If this distance is incorrect, two problems can occur:
Both scenarios create inconsistent readings. Once the package reaches the target position, the scale begins sampling at 1,000 times per second, so timing is everything.
3. Weighment Time
This setting, which some systems refer to as the “Ring Buffer,” determines how long the scale gathers samples. Since the system samples at 1,000 times per second, a 50-millisecond weighment time equals 50 samples.
I recommend starting with 50 ms as your baseline. Sometimes you can run longer, sometimes you can't, all depending on several factors:
Generally, the more time you give the system, the better your accuracy will be—as long as the package remains fully on the weigh conveyor during the entire weighment window. When we look at the graphing screen later, you'll see exactly why this detail matters.
4. Scale Filter
Most customers never need to adjust this setting. We ship 99% of our systems with the correct filter already configured based on the specifications that have been provided by the customer prior to delivery of their checkweigher.
Here's what you need to know:
Too much filtering (a low number) slows down the cell's reaction time, especially during short weighments. This causes the displayed weight to appear lower than it actually is. You'd be surprised how many customers unknowingly turn the filter way down and completely wreck their accuracy. Unless you have a specific reason to change it, leave this setting alone.
Step 1: Perform a Full Static Calibration
The HMI (Human Machine Interface) will walk you through every step of the calibration process. Follow the on-screen instructions carefully, and you'll be fine. This establishes your baseline accuracy.
Step 2: Set Dynamic Offset to 0
We don't want any offsets applied during the repeatability test. We're testing the system's inherent accuracy, not compensating for known differences yet.
Step 3: Turn Auto-Zero Off
The auto-zero feature will mask or distort your test results. Disable this feature temporarily so you are able to see the system's true performance.
With these three steps complete, you're ready to run your repeatability test.
I recommend running 30 passes of the same container. There's a specific screen in the HMI where you can clear previous weights, run your test, and watch the standard deviation trend over the run in real time.
Two crucial points about running this test:
1. Consistency is critical. Place the package the same way every single time. Orientation matters. A package placed lengthwise may weigh differently than one placed crosswise, even though it's the same product.
2. Stability matters. There should be no rocking, no air pockets, nothing that creates instability. Rigid containers should be stable. Stand-up pouches shouldn't wobble across the belt. Any movement during weighing creates inconsistency.
As you run the test, the standard deviation updates in real time. By the end of 30 passes, you'll see where the system stabilizes. Remember, you're targeting 0.5 grams or less. If your standard deviation is significantly higher, something in your setup is off.
The weight curve shows three distinct phases:
1. A rising slope as the container enters the weigh cell
2. A flat plateau when it's fully positioned on the cell
3. A downward slope as it exits
For consistent accuracy, your weighment window (between the green and purple lines) must capture the flat plateau. If your window captures too much of the rising or falling slope, you'll get inconsistent readings.
How to adjust:
Keep adjusting until the weigh window sits squarely over the plateau, then rerun your 30-pass test. This process is iterative. Don't expect perfection on the first try.
One important note: at this stage, we don't care what the actual number is compared to a bench scale. That comes later when we set the offset. Right now, we're only concerned with repeatability—making sure the system gives consistent readings.
Most customers don't understand how these four settings work together. Once they grasp the theory of operation, improvements come quickly. But I see a few recurring problems:
Operators like to tinker. They press buttons because they can. They don't necessarily trust the accuracy at first—especially if their previous checkweigher wasn't very good—so they keep adjusting things unnecessarily.
Self-installation without training. Many customers install the checkweigher themselves, and we don't always provide startup training for these units. They assume whatever accuracy they're getting is normal, even when it could be significantly better.
Filter adjustments. This is the big one. Customers change the scale filter setting without understanding the consequences, then wonder why their accuracy dropped.
For 90% of applications, proper checkweigher setup takes about 30 minutes. High-speed applications can take much longer—one of our technicians spent an entire day last week tuning a very high-speed production line. But for typical speeds and standard applications, you should expect to invest about half an hour to achieve a solid, accurate setup.
Checkweigher accuracy isn't magic. It's a matter of understanding how your system works and taking the time to tune it properly. Focus on repeatability first, use the trending graph to optimize your weighment window, and resist the urge to constantly adjust settings once you've achieved good results.
With these fundamentals in place, you'll have confidence in your quality control process and the peace of mind that comes from knowing every container is accurately weighed.
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