Standard Operating Procedure SOP for Calibrating Equipment

STANDARD PROCEDURE FOR CALIBRATING EQUIPMENT

Calibrating equipment is an essential process in maintaining the accuracy and reliability of any measurement system. Calibration involves comparing the readings of a device with a known reference standard, making adjustments as necessary, and certifying its accuracy within an acceptable range. Without proper calibration, measurements taken by the equipment may be inaccurate, leading to costly errors and potentially dangerous situations. Therefore, it is crucial to follow the correct procedure for calibrating equipment. In this blog post, we will discuss the step-by-step process for calibrating equipment.

Step 1: Identify the equipment to be calibrated

The first step in calibrating equipment is to identify the specific device that requires calibration. This could be any instrument that measures a physical parameter, such as temperature, pressure, or electrical signals. It is important to identify the correct equipment to ensure that it is calibrated according to the manufacturer's specifications.

Step 2: Identify the reference standard

Once the equipment to be calibrated is identified, the next step is to choose a reference standard to compare the readings. The reference standard should be of higher accuracy than the equipment is calibrated and traceable to a national or international measurement standard. Common reference standards include calibrated weights, temperature probes, or electrical standards.

Step 3: Prepare the equipment for calibration

Before calibration, it is essential to ensure that the equipment is in good working condition. This may include cleaning the equipment, replacing batteries or damaged parts, and checking the firmware and software versions. It is also important to ensure that the equipment is in a stable environment, free from any external factors that may affect the calibration process.

Step 4: Perform the calibration

The calibration process involves comparing the readings of the equipment with those of the reference standard. This is done by following the manufacturer's instructions or using a calibration procedure established by a reputable calibration laboratory. The readings of the equipment and the reference standard are recorded and compared to determine if any adjustments are required. If necessary, adjustments are made to the equipment to ensure that the readings are within the acceptable range. The calibration process is repeated until the equipment meets the required specifications.

Step 5: Document the calibration

The calibration process must be documented to provide a record of the calibration results. The calibration certificate should include the equipment's identification number, the date of calibration, the reference standard used, the calibration procedure followed, and the calibration results. This document provides evidence of the equipment's accuracy and traceability to the reference standard.

Step 6: Schedule regular calibrations

Equipment calibration is not a one-time process; it is an ongoing requirement to maintain the accuracy and reliability of the equipment. Regular calibrations should be scheduled based on the equipment's usage and the manufacturer's recommendations. This will ensure that the equipment remains in good working condition and meets the required specifications.

In conclusion, calibrating equipment is a critical process that should be performed correctly to ensure that the equipment provides accurate and reliable measurements. By following the six-step procedure outlined above, you can ensure that your equipment is calibrated correctly and meets the required specifications. Remember to document the calibration process, schedule regular calibrations, and seek assistance from a reputable calibration laboratory if necessary.

Example :

Equipment Checked: Scales (Balances)

Reference Documents: NIST Handbook 44, AASHTO M231, ASTM E617, ASTM C138 

Purpose: To provide instructions for checking the accuracy of scales to be used in area and project labs. 

All scales shall be checked annually. 

Inspection Equipment: Suggested standard weights (checked against calibrated scale) 100g, 200g, 5kg, 10kg, 20kg. 

Tolerance: The allowable tolerance throughout the range checked shall be equal to or less than 0.1% of the test load. The allowable tolerance for Platform scales used to determine fresh concrete unit weight shall be equal to or less than 0.3% of the test load. 

Procedure: 

1. Set up the scale in a location away from drafts or excessive air movement. 

2. Level the scale, and if weighing under water, observe that the apparatus is free of any obstruction that may affect its movement. 

3. Perform Span Check: Place the verification weights in the center of the scale. Record the weight to the readability of the scale. Confirm repeatability by placing one of the weights on the scale a second time to obtain the same weight. Confirm that the reading returns to zero when the weights are removed. 

• For weighing devices with a capacity of up to 1,000 grams, the suggested verification weights are 100g and 200g. External scale calibration weight shall be 200g. 

• For 12kg weighing devices, suggested verification weights of 5kg and 10kg. External scale calibration weight shall be 10kg. 

• For 30kg weighing devices, suggested verification weights of 10kg, and 20kg. External scale calibration weight shall be 20kg.

 • For platform weighing devices used for standard density determination, the suggested verification weights are 10kg and 20kg. Note: It is desirable to perform additional checks on scales for accuracy after they have been installed in the construction field lab. Not all verification weights are required for additional field checks. 

4. Perform Cornerload Check: Place the weight in the center of the scale and re-zero the scale. Place the weight in the four locations (Front/Back, Left/Right) as indicated on the Calibration Sheet. Record the weight of each reading. • For 12kg and 30kg weighing devices use a verification weight of 5kg. 

5. If any readings indicate out of tolerance, perform external scale calibration, if applicable, as per the scale instruction Manual and repeat steps 3 and 4, or remove the scale from service until it can be recalibrated. 

6. Record results on Balance or Scale Calibration Sheet