KANATA, Ontario The dictionary definition of calibration is "to determine by measurement or comparison with a standard, the correct value for each scale reading on a device" (McGraw-Hill, Dictionary of Scientific and Technical Terms, Fifth Edition).
If you are a consultant or blast contractor, you assess risk every day. But, have you considered the importance of, and the risks associated with, the calibration of your seismograph and the accuracy that is provided? Can your calibration provider back you up in times of trouble and provide documented evidence that the equipment was functioning within specification? Can their calibration procedures withstand independent scrutiny and be shown to be traceable to national standards for accuracy of measurement? These are important documents that in court provide tremendous support that blasting and monitoring activities are conducted professionally and competently.
Why Calibration is Important
Calibration is important to ensure the instrument is performing as it was designed to, and measures accurately the true ground vibration and air-blast. Although seismographs are designed to be used in a rugged environment, they are still sophisticated electronic monitoring devices. Therefore, preventive maintenance becomes an important part of the calibration process. Many manufacturers and their authorized calibration facilities will perform upgrades and preventative maintenance on your instruments, often free of charge, providing the units are regularly serviced. The upgrades often include product enhancements of both hardware and software, and result in expanding the functionality of the equipment.
The recommended interval for calibration of most measuring equipment including seismographs is one year. Across most of North America and many parts of Europe regulatory authorities actually require seismographs to be calibrated on an annual basis. This requirement has been or is being adopted by several other countries around the world and some specific projects even require that seismographs be calibrated every three or six months.
What the Calibration Certificate Means
When your seismograph is calibrated by an authorized calibration facility, the facility will issue a calibration certificate. The certificate provides the list of reference equipment used in the calibration process. In order for the calibration to have any validity, this reference equipment must be itself calibrated by equipment, which is traceable to a nationally recognized standard, such as the National Institute of Standards and Technology (NIST) in the United States, or the National Research Council (NRC) in Canada. The calibration certificate should also contain the model, serial number, date the instrument was calibrated and who performed the calibration. Should an authority question your seismograph records, this certificate is the document that provides proof of professional calibration.
The reference equipment used in the calibration process must be even more accurate than the equipment being calibrated. The reference equipment must itself be calibrated by even more accurate equipment that is traceable. Needless to say, the agency performing the calibration must be qualified to do so.
Importance of Manufacturer-Certified Calibration
There are individuals and companies worldwide that are not certified by the manufacturer to perform seismograph calibration, yet continue to do so. It is in your best interest to have your seismograph calibrated by the specific manufacturer or their authorized agents.
The key factor is the integrity of the measured record if it is ever called up as evidence in a court of law. Using a manufacturer-certified facility ensures that proper procedures are followed when calibrating your seismograph. This removes any uncertainty associated with the reliability and measurement accuracy of your seismograph. Using unauthorized facilities may cause problems in court if the reference equipment is not traceable, or if the certification documents are incomplete. In some instances, unauthorized facilities have even been found to calibrate equipment without ever updating the calibration date within the instrument. If an improper calibration date is printed on vibration records, it may call into question the validity of the report itself.
Also, if a seismograph does require repair, the manufacturer has the best experience and knowledge to find and fix the problem. They will also ensure that any replacement parts that are used meet the specifications for the equipment. Unauthorized facilities do not have access to test specifications, procedures or parts lists and some of these facilities may use substitute parts that do not meet the functional requirements. This can ultimately lead to inaccurate vibration levels being reported.
When you send your seismograph out for its annual calibration remember to manage the associated risk. The factors listed above will help to lower your risk and provide assurances to the regulatory authority that you are proactively monitoring your vibration levels.
(This item was submitted by Instantel, a leading Canadian manufacturer of seismographs for a wide variety of applications. It was edited by CMJ. See the Instantel web site at www.instantel.com.)