The recommended calibration interval for most equipment, including seismographs, is one year. Across most of the North American territory and in many European regions, regulatory authorities require that seismographs are calibrated annually. This requirement has been or is being adopted by many other countries in the world, and certain projects require that seismographs are calibrated every three or six months.
Calibration is important for the tool to work as designed and to directly measure the actual vibration of the ground and the blow of the explosion. Although seismographs are designed for use on rough ground, they are nevertheless sophisticated electronic monitoring devices. Thus, preventive maintenance is an important part of the annual calibration process.
Some seismograph models are designed with geophone, microphone and data acquisition unit calibrated as a system. In general, this allows for the entire system to be calibrated more accurately. However, tools calibrated by this method are limited by the fact that the geophone and microphone match the data acquisition unit, and the sensors cannot be changed with those of other tools without affecting overall accuracy, even though they are of the same model produced by the same manufacturer. Other seismograph models are designed with the geophone, microphone and data acquisition unit calibrated as independent units.
It is in your best interest to have your seismograph calibrated by its manufacturer or its authorised agents.
Also, if a seismograph needs to be repaired, the manufacturer has the necessary experience and know-how to identify and solve the problem. At the same time, the manufacturer will make sure that spare parts comply with the specifications of the equipment. Unauthorised institutions do not have access to testing specifications, procedures or spare part lists, and they can use alternative spare parts that do not meet the functional requirements.
In order to achieve safe initiation and to prevent misfire, electric blasting circuits must be checked in terms of continuity and resistance before being connected to the firing source.
Control equipment for continuity of blasting circuits is used to check current flow. Such equipment only checks whether the circuit is closed or not. If the equipment does not indicate circuit continuity, it means that the circuit is interrupted and sections of it must be checked to detect the failure.
Specially designed and certified ohmmeters are used to check ohmic resistance of the circuit and circuit continuity.