Calibration intervals

The question is often asked. How often should calibration be carried out Is it sufficient to do it once, or should it be repeated The answer to this question depends on the instrument type. A very simple instrument that is robust and stable may require calibrating only once during its lifetime. Some fundamental meters do not need calibration at all. A Pitot-static tube or a liquid U-tube manometer are examples of such simple instruments. On the other hand, complicated instruments with many components or sensitive components may need calibration at short intervals. Also fouling and wearing are reasons not only for maintenance but also calibration. Thus the proper calibration interval depends on the instrument itself and its use. The manufacturers recommendations as well as past experience are often the only guidelines. 

Have calibration intervals been established for all reference standards and measuring equipment based on the equipment manufacturer s recommendations or knowledge of equipment stability, purpose, and level of usage ... 

Are trend data reviewed from previous calibration records to adjust the calibration intervals ... 

How often should chamber controllers be calibrated Chamber controllers should be calibrated a minimum of every six months. If controllers pass consecutive calibrations successfully, consideration should be given to extending the calibration interval. 

It is also beneficial to tag the instrument so that it can be labeled with the date the next calibration is due. This allows the operator to verify the instrument is within its calibration interval. 

Calibration should be conducted on a regular interval basis. Simmons [22] recommends a regular calibration interval of every 3 months. 

Abstract Since the uncertainty of each link in the traceability chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time, the chain lifetime is limited. The lifetime in chemical analysis is dependent on the calibration intervals of the measuring equipment and the shelf-life of the certified reference materials (CRMs) used for the calibration of the equipment. It is shown that the ordinary least squares technique, used for treatment of the calibration data, is correct only when uncertainties in the certified values of the measurement standards or CRMs are negligible. If these uncertainties increase (for example, close to the end of the calibration interval or shelf-life), they are able to influence significant-... 

According to the definition [1] the traceability chain is the unbroken chain of comparisons or calibrations from the result of a measurement or the value of a measurement standard to the national or international standards, all having stated uncertainties. The uncertainty of each link in this chain (measuring analytical instrument, reference material or other measurement standard) changes over the course of time. Therefore, the calibration intervals of measuring equipment used in testing (analytical) laboratories [2, 3] and of measurement standards used for their calibration are very important. The same applies to the shelf-life of a certified reference material (CRM) as a measurement standard. So, taking into account these... 

Stability of the traceability chain in chemical analysis is dependent on the calibration intervals of measuring equipment and shelf-life of CRMs used for the calibration of the equipment. 

NCSL RP-1. Recommended Practice (1996) Establishment and adjustment of calibration intervals, 3rd edn. Boulder, USA... 

A calibration programme should be available and should provide information such as calibration standards and limits, responsible persons, calibration intervals, records and actions to be taken when problems are identified. 

Virtually all analytical test methods require some form of calibration or verification before actual samples are analyzed. Different test methods require different calibration intervals. Thus, a decision about appropriate calibration fiequency must be made on a case by case basis. There is a tendency among many laboratories to do the bare minimum calibrations similar to their approach toward quality control requirements. This is not the way to achieve superior performance. Moreover, if an instrument is out-of-calibration, under no circumstances can data fiom that instrument be reported to the customers. 

An important aspect of calibration is the decision on calibration intervals, i.e., the maximum period between successive recalibrations. Two basic and opposing considerations are involved the risk of being out of tolerance at any time of use and the cost in time and effort. The former should be the major concern because of the dilemma of what to do with the data obtained during the interval between the last known in and the first known out of calibration. However, an overly conservative approach could be prohibitively expensive. A realistic schedule should reduce the risk of the former without undue cost and disruption to work schedules. The factors that need to be considered in a realistic schedule include ... 

Other difficulties mentioned which cause errors can be illustrated with use of Eq. (2). This can be written for the bell prover arrangement, for a finite calibration interval At, as... 

NDIR sensors are also extremely stable, quick to respond to gas, can tolerate long calibration intervals, and have a wide working range (sub-ppm to... 

Before conducting the test, the lead block of the same casting should be calibrated. The calibration is performed with a pure picric acid whose density is 1 g/cm and charge volume is 10 cm. The net-expansion value of such an explosive charge, obtained in three shots, should ammmt to between 287 and 300 cm. However, the values between 280 and 310 cm can also be accepted. In that case, conversion of the net-expansion values obtained shmild be made. The conversion is obtained by multiplication of the calibration net-expansion value by the quotient of the mean value of the admissible calibration interval (294 cm ) and the obtained value. 

B. McGarthy, C. Vaughan, B. O Flynn et al, "An examination of calibration intervals required for accurately tracking blood pressure using pulse transit time algorithms," Journal of Human Hypertension, vol. 27, no. 12, pp. 744-750, Dec 2013. 

Instruments may be calibrated on different schedules. The drift used should be based on instrument-specific calibration intervals, including allowable extensions for calibration intervals. When the manufacturer s specification for stability (drift) is unavailable, 50% of the instrument calibration accuracy per year is commonly assumed. 

The calibration of the potentiometric ceil should be made at the same temperature as the sample measurement. In principle, it is desirable to calibrate in direct connection with the sample measurement. When samples are continuously processed, a routine should be set up for calibration intervals (number of samples to be run between calibrations). The calibration interval depends on the stability of the potentiometric cell (the condition of the electrodes, the stability of the mains voltage supply, interference from other sources). For each calibration and sample measurement, the temperature is registered and b and Ex measured. The sample pH is estimated from the measured Ex and E pHe calculated with Eq. (7-16), which are all put into Eq. (7-14) for calculation of pH . If the measurements are made in an estuarine environment, the salinity of the sample must be taken from the CTD measurement for selection of the right buffer to use for the calibration. 

The effect tends to increase with reduced system lengths (capillary system) and is probably caused by isomerization of the -isomer of silicomolybdic acid. Temperatures of ships laboratories often are notoriously variable. If the ambient temperature varies by more than about 3 K within a calibration interval, the manifold should be thermostatically controlled. This may be done by either using a thermostated test-tube as a coil core for the mixing and reaction coils (shaded rectangle in Fig. 10-12) or deploying the coils in a water bath. 

Low Maintenance Costs Six to twelve months calibration intervals, the longest in the industry, cuts maintenance costs in half ... 

Assure that equipment is lirequendy checked by periodic system or cross-checks in order to detect damage, inoperative instruments, erratic readings, and other performance degrading factors that cannot be anticipated or provided for by calibration intervals ... 

Adherence to the checking schedule makes or breaks the system. The interval should be based on stability, purpose, and degree of usage. If initial records indicate that the equipment remains within the required accuracy for successive calibrations, then the intervals may be lengthened. On the other hand, if equipment requires frequent adjustment or repair, the intervals should be shortened. Any equipment that does not have specific calibration intervals should be (1) examined at least every six months, and (2) calibrated at intervals of no longer than one year. Adjustments or assignment of calibration intervals should be done in such a way that a minimum of 95% of equipment, or standards of the same type, is within tolerance when submitted for regularly scheduled recalibration. In other words, if more than 5% of a particular type of equipment is out of tolerance at the end of its interval, then the interval should be reduced until less than 5% is defective when checked. 

After the response functions are plotted from these analyses, one proceeds with the quality control analysis of the samples. The procedure is again using samples of blank matrices spiked in analytes at concentrations chosen by the user over the whole range of the calibration interval. These samples are analyzed based on the response functions plotted to evaluate the accuracy, repeatability, and intermediate fidelity of the method. The concentrations of the quality controls and the results obtained for cocaine from these samples are given in Table 7.3. 

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