How to Calibrate a Load Cell: Step-by-Step Guide

Even a high-quality load cell drifts over time. Shocks, temperature swings, mechanical wear and small changes in the structure can all move the readings away from the true value. Calibration brings the output back in line with a known reference so the weight displayed is the weight on the scale. This guide walks through the practical steps for a load cell connected to an indicator or controller, and explains the mistakes that most often cause trouble.

What calibration actually does

A load cell produces a tiny electrical signal. An indicator converts that signal into engineering units such as kilograms. Calibration teaches the indicator the relationship between the signal and a known weight by recording two key points: zero, the signal with no load, and span, the signal at a known load. Additional checks confirm that the readings are accurate between those two points.

Before you start: preparation

Good preparation is half of a good calibration.

• Use certified test weights. Their accuracy must be several times better than the accuracy you want from the scale. Aim to cover at least half the working capacity, and preferably more.
• Warm up the system. Switch on the indicator and cells for the time recommended in the manual, often 15 to 30 minutes.
• Check the mechanics. Confirm the platform or vessel is level, free to move and not touching pipes, hoses, conduit or guards. Binding is the number one cause of repeatability problems.
• Check the electrical connections. Look for damaged cables, wet junction boxes and loose terminals. If you need to confirm the wire functions, see load cell wiring colours.
• Stabilise the environment. Avoid wind, vibration and large temperature changes during the test.

Step 1: Zero or dead-load calibration

With the empty platform, tank or hopper in place, record the zero. This captures the weight of the structure itself, called the dead load, so it is not counted as product. Make sure nothing else is resting on the weighing system. After entering the zero, watch the reading for a minute. A reading that wanders steadily indicates a problem such as moisture in a cable or a mechanical rub.

Step 2: Span calibration

Apply a known weight and enter its value into the indicator. The instrument calculates the scale factor between the signal and weight. For best accuracy:

• Use a weight as close as practical to the working capacity.
• Place the weight in the centre of the platform for single-cell scales, or distribute it evenly for multi-cell scales.
• Allow the reading to settle before entering the value.

If you cannot use test weights equal to the full capacity, some indicators allow a substitution method or a theoretical calibration based on the cell’s mV/V rating. Those methods are useful for large tanks, but they are less accurate than real weights because they do not account for installation effects.

Step 3: Linearity check

Add weights in stages, for example 20%, 40%, 60%, 80% and 100% of the test range, and write down each reading. Then remove the weights in the same steps and record the readings again. Compare the values:

• A straight, repeatable relationship means the system is linear.
• Different readings on loading and unloading show hysteresis, often caused by friction or binding in the mounting.
• A curve that bends away from the line suggests overload damage or a problem with the cell.

Step 4: Corner or shift test for multi-cell scales

Platform and tank scales use several cells whose outputs are summed in a junction box. Place the same test weight on each corner and in the centre, and record each reading. They should match within the permitted tolerance. If a corner reads high or low, the fix may be adjusting trim potentiometers in the junction box, levelling the foundation or correcting a mounting problem.

Step 5: Repeatability test

Apply the same weight several times and record the reading each time. Results should repeat within a narrow band. Poor repeatability points to a mechanical rub, loose mounting, electrical noise or a damaged cable.

Step 6: Document everything

Write down the date, test weights used and their certificate numbers, the readings at each point and the person who carried out the work. A record of past calibrations shows how the system drifts and helps you decide on service intervals. It is also essential for quality audits.

How often should you calibrate?

The interval depends on how critical the measurement is and how harsh the environment is. Many sites check monthly or quarterly and fully recalibrate at least once a year. Check more often after any mechanical change, repair, overload event or if readings start to drift.

Common causes of calibration problems

Symptom	Likely cause	What to check
Zero drifts steadily	Moisture or damaged cable	Junction box, cable glands, connectors
Readings differ between corners	Uneven foundation or cell mismatch	Levelling, mounting hardware, trim adjustment
Different readings loading vs unloading	Friction or binding	Pipes, hoses, guards touching the structure
Output does not return to zero	Overload or permanent deformation	Inspect the cell, replace if damaged
Noisy or jumping readings	Electrical interference or vibration	Shielding, grounding, cable routing, filter settings

Trade use and legal requirements

If the scale is used to buy or sell goods by weight, Australian trade measurement law applies. The instrument normally has to be of an approved pattern and verified and certified by an authorised person, and a self-calibration does not replace this. Check with the National Measurement Institute or your state or territory regulator before using a scale for trade.

Choosing test weights and standards

The quality of your calibration depends on the quality of your reference. Test weights should be certified and traceable, and their accuracy should be several times better than the tolerance you need from the scale. Handle them with care, since fingerprints, rust and dents change their mass. For large tanks and silos where adding thousands of kilograms of weights is impractical, techniques such as substitution weighing or using a calibrated reference load cell in line can help. Record the certificate and expiry date for every weight you use.

Environmental factors to control

Load cells respond to temperature, and the structure holding them can expand and contract. Calibrating on a hot afternoon and operating on a cold morning can create small shifts. Wind on an outdoor platform, vibration from nearby machinery and even the pressure of a hose or cable can add noise. Where possible, calibrate under normal operating conditions and note the temperature on your record, so you can explain any seasonal differences later.

Frequently asked questions

Can I calibrate without test weights?

Theoretical calibration using the cell’s rated output is possible and useful for large tanks, but real weights give a more accurate result because they include the installation effects.

Why does my scale read correctly at one weight but not another?

That points to a linearity problem, usually from mechanical binding, an overloaded cell or a poor span value. Run the staged linearity check described above.

Do load cells need replacing if they drift?

Not always. Many drift problems come from wiring, moisture or mounting. Check those first and replace the cell only if the problem persists after repairs.

Working in Western Australia? See our page on load cell calibration in Perth. To understand the sensor itself, read how a load cell works and the full Load Cells Australia guide.

Talk to Sands Industries

Not sure which load cell, capacity or accessory fits your application? Contact Sands Industries with your capacity range, accuracy needs and operating environment, and we will help you shortlist the right option.

Keep reading

• Load Cells Australia – Accurate Measurement Solutions by Sands Industries
• Load Cell Wiring Colour Code: How to Identify the Wires
• How Does a Load Cell Work – The Science Behind Accurate Industrial Measurement