Calibration of industrial platform weighing scale

How do you calibrate a weighing scale?

Purpose and Scope:

• This procedure explains in detail how to calibrate industrial Weigh Scale using standardized weights.
• To outline the procedure to be followed and the individuals in charge of carrying out and recording the calibration of industrial weigh scales.
• To provide workers instructions on how to carry out calibration tasks consistently and to guarantee that the results of needed calibration tests are reported in a consistent manner.

Tools required for Weighing scale calibration:

• Necessary hand tools.
• Standard certified test weights
• Lifting tackles for standard weights
• Lifting equipments or mobile crane or fork lift
• Compressed air or blower cleaning the platform
• Multimeter.
• Test leads and probes.
• Soft Cloth for cleaning.

Safety

• For specifics on fundamental safety, general recommendations, and calibrating operations in process industries, please click the link provided below.

Basic Safety and General Considerations for Process Industries Calibration Process

• Locate the platform weigh scale that you want to calibrate. Make sure the weigh scale is the right one and write down any important information on the tag, such as the manufacturer, model number, range, etc.
• Disconnect the power supply to the weigh scale. Ensure that any nearby junction boxes or marshalling panels close to the control room have their power sources switched off.(For instance, shut off the circuit breaker or unplug the wires).
• Before calibrating the platform weigh scale, the calibration area should be blocked off with barricades, and the process area should have the appropriate signboards placed to redirect traffic there.
• Carefully unplug the electrical connection from the weigh scale. Make sure to follow any safety rules (like wearing insulated gloves or equipment) and be careful not to damage the wires or connections.
• Always make sure you are following the lifting standard when it comes to lifting activities, managing lifting equipment, and material handling in accordance with organization and local policy.
• Keep in mind that depending on the particular equipment and process location, this general technique for calibrating weighing scales may need to be modified. Always follow any manufacturer instructions and local safety regulations when working with weighing scales or other process equipment.
• To prevent an unauthorized power on to the scale, adhere to all applicable lockout/tagout protocols. A barricade should be used to keep the weighing scale apart from the process, and traffic flows should be established for the movement of other process equipment.
• Follow any safety protocols specific to your industrial setting, such as wearing appropriate personal protective equipment (PPE).

Calibration Setup

• There are no vibrations or electromagnetic interferences in the calibration area. The calibration space must also be brightly lit and well-ventilated.
• Gather all of the necessary tools, standard weights, and lifting gear.
• Gather all required documentation, such as an instrument loop diagram. Instrumentation data sheet, communication parameters, etc.

Calibration principle

• The calibration principle for a platform weighing scale involves comparing the output of the scale to a known reference weight to ensure accurate and consistent measurements. 

How do you calibrate a weighing system?

Calibration procedure

• Ensure that there is enough space around the base of the scale for the procedure to take place safely.
• Scales should be cleaned using compressed air or a blower.
• Before cleaning, check the scale for any indications of wear, breakage, or loose connections that may need rectification. Before moving further with the calibration, contact an expert for troubleshooting if any problems are found.
• Check to make sure there isn’t any buildup of process material between the platform and the ground. Accuracy of the calibration is impacted by certain types of buildup.
• With the use of the instrument data sheet, confirm the configured parameters of the weighing system control unit, such as the load cell sensitivity value, excitation supply voltage, display resolution, unit of measurement, and etc.
• Verify the state of each load cell’s cable and load cell mounting on the platform weigh scale. Additionally, look for any loose wire connections in the load cell.
• Obtain a known reference weight that is traceable to a national or international standard. Make sure the reference weight is appropriate for the scale’s capacity and within the range of weights you typically measure.
• Test Weight should be less than or equal to the whole range of the scale but larger than 50% of that range.
• Standard weights traceable to SI units of mass should preferably be used as test loads.
• Switch on the weighing control device after cleaning it.
• Allow the weighing system to stabilise in the calibration area environment for at least one hour before performing measurements, and ensure that it has had enough time to warm up in accordance with the manufacturer’s instructions.
• Validate the current calibration of test standards.
• Check the zero indication on the weighing system control unit and make any necessary adjustments.
• If the scale has a tare or zero function, press it to set the scale to zero before calibration. This step ensures that the scale does not include any residual weight from previous measurements.
• position the known reference weight on the scale platform. Ensure that the weight covers the entire platform area and is centered for accurate results.
• Note the value displayed on the scale. This is the measured weight according to the scale.
• Compare the scale reading to the known reference weight. If there is a significant difference between the two values, calibration adjustments may be necessary.
• Follow the Weighing scale manufacturer’s instructions to make the necessary adjustments. It’s crucial to make precise and incremental adjustments to bring the scale readings in line with the known reference weight.
• After making adjustments, repeat steps for multiple times until the scale consistently provides accurate readings within an acceptable tolerance.
• Depending on the specific weighing system being installed, the calibration process may need to be modified. Because of this, before starting, please read the manufacturer’s instructions.

Eccentricity Test

• Place the test load at various locations on the platform so that the load’s center of gravity occupies each location.

Center (Position 1)

Front Left (Position 2)

Front Right (Position 3)

Back Left (position 4)

Back Right (Position 5)

• The test load needs to be at least three times the smaller weighing range.
• Position the first test weight on the center of the scale platform. This weight should be within the scale’s capacity and aligned with the center of the platform.
• Note the weight value displayed on the scale when the first test weight is placed on the center of the platform.
• Carefully move the test weight to a specific distance from the center of the platform*position 1), as determined by the eccentricity distance(position2).
• Once the test weight is at the designated eccentricity distance, note the weight value displayed on the scale.
• With test weight, check the weighing system’s response in each platform corner and once more in the center.
• Keep track of the weighing system’s indication for each test weight position. Check the weighing system’s zero indication after removing each test weight.
• Compare the scale readings at the center and the eccentricity distances for each test weight. If the readings deviate significantly, it indicates that the scale has eccentricity errors. The magnitude of the errors can help assess the scale’s performance and determine if adjustments or corrections are necessary.

Recording calibration

• Utilize test weights to determine the scale’s repeatability across various ranges. in order to confirm that the weighing device is producing accurate output values.
• If the output result is outside of a range that is considered acceptable, re-calibration is required. 
• If the calibration and eccentricity test  errors  are beyond acceptable limits, consult the manufacturer’s guidelines for recommended corrective measures. This may involve adjustments to the scale’s hardware or software settings to minimize the errors.
• No additional calibration is required for weighing system if every output value (+/-%) falls within acceptable bounds.

Completion of calibration

• A calibration sticker must be attached to the weighing system once the necessary calibration has been completed to indicate the system’s calibration state.
• If the calibration result exceeds or falls short of the permitted limit, it must be clearly stated on the labeling of the weighing equipment.
• Make sure that all test equipment, test weights, measuring equipment, and devices are installed in their designated field locations or are returned to their respective locations or specified areas once the calibration is complete. 
• Make that the area where the weighing system calibration is being done is tidy.
• Remove the barricade and traffic diversion, as well as the weighing system’s isolation.
• After the calibration work is finished, make sure the weighing system is secure and functional.

Sample weighing scale calibration report

The following image illustrates an industrial platform weighing scale calibration sample report that was done in a process area using standard weights as the reference.

The link below allows you to obtain the Excel template that was used to create the industrial platform weighing scale calibration report.