If you’ve ever had to get a multi-cell weighing system up and running or have gone through the process of servicing one, you’ve probably run into a pretty common problem at some point:
You’ve got a scale where each corner is reading something just a little bit different.
Even when load cells are properly put in place, levelled out, and tightened down correctly, the
reality is that they don’t always share the load perfectly on their own. Small variations in mV/V output, structural stiffness, cable length, and mounts can all produce little differences in readings. And when these differences get too big, you’re looking at potential problems with accuracy, repeatability, and even legal-for-trade compliance.
This is where load cell trimming comes in.
Load cell trimming makes sure that you get the same reading from a known test weight no matter where it’s placed on the platform, whether it’s in the front left corner, the back right, right in the middle or anywhere in between.
This article explains just what trimming is, how it works, when you might need it, some common mistakes to avoid and how to do it the right way.
What Is Load Cell Trimming?
Load cell trimming (also known as corner trimming, section adjustment, or load cell signal balancing) is the process of adjusting the output of load cells that are reading a bit higher than the others in a multiple load cell system, electrically.
When load cells are manufactured, they’re all calibrated and matched to meet their specs. But after installation, it’s only when they’re working together in a multi-cell system or during troubleshooting that trimming comes into play.
The main goal is simple: to get an equal response across the platform for consistent, accurate weighing.
Some key points that engineers need to know:
- Trimming can only reduce a load cell’s signal. You can’t increase it without replacing the cell or making some mods to it.
- The weakest cell ends up being your reference, all the other cells are trimmed down to match it.
- Trimming happens inside a junction box. What you use to do the trimming is potentiometers (”trim pots”) in the summing card which applies resistance to the stronger load cells to equalize the combined cell signals.
And a key fact: 99% of analog summing cards trim by putting a high-value potentiometer in the excitation leg, not the signal leg.
That means:
- Turning counter-clockwise tends to increase the reading in most systems
- Turning clockwise tends to decrease it (and it’s just the opposite of what most people would guess).
Is Load Cell Trimming the Same as Calibration?
No, this is one of the biggest misconceptions – trimming and calibration are definitely not the same thing
Here’s the Distinction:
| Term | What It Adjusts | Purpose | Frequency |
|---|---|---|---|
| Load Cell Trimming | Output balance between corner cells | Ensures identical section readings | After installation, cell replacement, or when corner variation >0.1–0.2% |
| Calibration | Zero & span of entire scale | Ensures overall accuracy | Annually or after repair |
| Zero / Span Adjustment | Baseline + full-scale response | Routine verification | Daily or weekly |
Trimming balances the corners, and calibration sets the scale’s actual accuracy. Both are pretty essential for performance.
When to Perform Load Cell Trimming?
Trim the system if the load distribution between cells has changed or can’t be confirmed:
- New scale installation
- After replacing one or more load cells
- After mechanical repairs or structural adjustments
- After an overload incident
- When corner variation exceeds 0.1–0.2%
- Before legal-for-trade certification
- After seasonal temperature swings or extreme weather
- Whenever there’s unexplained drift
Mechanical Equalization vs. Electrical Trimming
Before even touching trim pots, any mechanical issues have got to be sorted out first. Trimming can’t fix structural or installation problems.
What Mechanical Equalization Fixes:
- Leveling the platform
- Shimming mounts
- Removing side loads or binding
- Replacing failed bearings or load cell cups
- Cleaning debris under the platform
What Electrical Trimming Fixes:
- Small differences in load cell output
- Corner load imbalance
- Unequal signal due to cable resistance differences
Only after the system is mechanically sound is it safe to start electrical trimming.
Tools Required for Accurate Load Cell Trimming
You need professional-grade tools to get the job done right:
Essentials
- Certified test weights (10-25% of scale capacity is usually a good starting point)
- An insulated precision screwdriver
- Junction box wiring diagram
- A stable weight indicator (first make sure you’ve got the right excitation voltage)
- Spirit level or laser level
Highly Recommended
- A digital multimeter
- Load cell documentation with mV/V specs
- A notebook or digital log for documenting results
Trim potentiometer direction can vary between manufacturers, so don’t just assume clockwise will always increase – it’s always best to check the documentation.
How Load Cell Trimming Works (Step-by-Step)
Step 1: Get the Scale Ready and Zoned
- Give the platform a good clean
- Make sure the mounts are all seated correctly
- Check the platform is level (within 3mm across the deck)
Step 2: Laying Out the Test Weight on Corner #1
Put the certified test weight right on top of the first cell section – try to get it spot on.
- Example: A 5,000-kilogram test weight on a truck scale capable of weighing 60,000 kilograms.
Step 3: Take Note of the Indicator Reading
| Corner | Before Trim (lb) | After Trim (lb) | Error Reduced (lb) |
|---|---|---|---|
| NW | 5.185 | 5.003 | -0.182 |
| NE | 4.920 | 5.002 | +0.082 |
| SW | 5.070 | 5.004 | -0.066 |
| SE | 4.975 | 5.001 | +0.026 |
| Centre | 5.210 | 5.005 | -0.205 |
It’s pretty clear here the cell (or section) is producing a bit too much output.
Step 4: Open the Junction Box & Find the Right Trim Pot
Take a look at the wiring diagram. Label the trim points if they’re not already. And if you’re having trouble, don’t be afraid to put a label or two on there to sort things out.
Step 5: Adjust the Potentiometer
It’s best to make your adjustments in 1 / 8 turn increments, which will usually result in an increase in the reading on most modern load cells… just remember to turn them anti-clockwise.
After every 1 / 8 turn, have a look at the reading on the indicator.
Step 6: Repeat the Process for All Corners (and Sections)
Take the same test weight and put it in each section in turn. Keep making adjustments until each corner is reading the same.
Step 7: Check the Center & Cross Load Positions
Try placing the weight:
- right in the center
- on the diagonal
- along the midpoints
If the readings in the centre are a bit all over the place, but the corners look spot on, then your issue is probably with the mechanics rather than the electronics.
Step 8: Lock & Seal
Add a tamper-evident coat of paint or some wire seals. And of course don’t forget to note down all the values.
Common Issues That Come Up When Trimming (And How to Fix Them)
1. Corner won’t bring itself into tolerance
Possible causes:
- The platform is binding
- The deck isn’t level
- The load cell is damaged
Fix: Tackle the mechanics first.
2. Trim pot is at its limit
Possible causes:
- The load cells are mismatched
- You’ve got the wrong capacity cell installed
- The junction box is wired up wrong
Fix: Double-check the mV/V output and the wiring.
3. System was good today, but drifting tomorrow
Common causes:
- Temperature swings
- Moisture has got into the junction box
- Loose connections
- Electrical noise or poor shielding
Fix: Double-check the grounding, seals and cable integrity.
4. Corners are perfect, but centre reading is way off
This is almost always a mechanical issue, just think about it:
- The frame is flexing
- Worn out suspension components
- The mounts are wrong
Fix: Have another look at the structural alignment.
Seven Costly Trimming Mistakes Techs Are Still Making
- Using uncertified forklift weights
- Adjusting the wrong potentiometer (yes, it happens!)
- Trimming with dirt, ice or grain stuck under the deck
- Making your adjustments in too big a jump
- Not re-testing the centre after making adjustments to the corners
- Not sealing the trim pots for legal-for-trade systems (comes back to haunt you, doesn’t it?)
- Failing to document it all (because of course you need to be able to prove it was done correctly!)
Frequently Asked Questions
How Often Should You Be Doing Load Cell Trimming?
After any big changes, and at least once a year. If it’s going to be out in the elements or subject to a lot of vibration, you might want to be doing it every 6 to 12 months.
Can Trimming Fix a Mechanical Problem?
No, it can’t. You need to fix the mechanics before you even start trimming.
Do Digital Load Cells Need Trimming?
Most of the time, no. Modern digital load cells can take care of themselves and don’t need manual trimming.
Why Can Trimming Only Reduce the Output?
Trim pots reduce the voltage, which means you can only reduce the reading on the load cell – not increase it.
How Long Does Trimming Usually Take?
Depends on the system size and how well the mechanics are holding up, but usually between 30 to 90 minutes.
Why is Load Cell Trimming Important?
Proper load cell trimming is one of the best ways to turn a standard weighing system into a precise and reliable measurement instrument. It keeps things fair, ensures compliance and stops you wasting time and money dealing with disputes and downtime.
If you’re setting up a new scale, trying to sort out a drift problem or just want to make sure your equipment is running at its best, then accurate trimming is just the ticket.
Need Help With Trimming, Diagnostics or Scale Performance?
Load cell trimming is precise work and small mistakes can lead to ongoing accuracy issues, failed inspections or unnecessary downtime. If you want confidence that your scale is properly balanced, calibrated, and performing as it should, Massload can help.
Massload supports industrial weighing systems with expert guidance on load cell trimming, scale calibration, diagnostics, and overall equipment performance. From new installations to troubleshooting persistent accuracy problems, our team helps ensure your weighing system delivers consistent, compliant, and repeatable results.
Contact Massload today to discuss your scale, weight accuracy, calibration needs, and weighing equipment performance.
