Frequency calibration

Bickel, H.J., Calibrated Frequency Domain Measurements Using the Ubiquitous, Spectrum Analyzer, Federal Scientific Monograph 2, January 1970. 

A note in clause 4.11.2 requires wear and frequency of use to be taken into account in establishing calibration frequency. 

The criticality designated to each instrument will form the basis for the calibration rationale and calibration frequency for the system instrumentation and regulating devices. For quality-related critical parameters the range and limits must be accommodated by the instrument calibration accuracy and failure limits.)... 

Other effects are negligible compared with these, but are discussed in [24] and [25]. The statistical uncertainty is mainly due to small temperature fluctuations of the tellurium cell these had periods of order minutes, and gave corresponding shifts of the calibration frequencies. The tellurium lines are relatively wide ( 20 MHz), but even so the uncertainty in the locking point could be reduced considerably by the use of a more sophisticated locking system. However, the main problem is the uncertainty in the frequencies of the transitions themselves. The final results for the IS - 2S frequencies are ... 

Calibration range required (to satisfy process requirements) Calibration frequency (e.g., 6 months, 12 months)... 

Calibration frequency and process limits should be defined for each instrument. 

There may be a large time gap between the IQ, OQ, and PQ phases for instrumentation associated with particnlar mamrfactnring processes dne to the site constmction program (e.g., unavailability of utilities, panels). As a resnlt, some control and monitoring instrumentation may need to be recalibrated prior to commencing OQ, and possibly again prior to PQ, depending on calibration frequencies. It would be advisable to recalibrate critical instrumentation anyway to ensure its status is known prior to OQ and PQ. 

After establishing the requirement, coordination committee, and pohcy, the next stage in the process is equipment procurement. This involves first identifying candidate POCT equipment having the prerequisite analytical and operational capabilities to meet the clinical requirements of a POCT service. As discussed in Chapter 15, the performance characteristics of these devices are then obtained and compared. These include parameters such as accuracy, precision, TAT, calibration frequency, potential interferants, calibrator... 

Complete calculations/example calculations, including calibration frequency and how calibration is performed... 

The key point in the consideration of maintenance and calibration frequencies is the necessary assurance of data validity. In certain cases it will additionally be necessary to ensure the traceability of the calibrations performed to national or international standards of measuremenf . Although this requirement may be seen to lean more towards the scientific side than to the side of reconstructability, in the sense that this traceability will provide... 

Expected calibration frequency for dyads. For dyads, two models are proposed. 

Quality control measurements can help a great deal in deciding what calibration frequency intervals should be used. 

The purpose of monitoring measurement and test systems is to determine whether the measurement system is stable, where stability is the absence of drift or other changes over time. This wiU ensure that the estimates of accuracy and precision remain the same over time. In many cases, when the measurement system is consistently stable over a long period of time, a reduced calibration frequency can be implemented. 

With fast electronic counters, frequencies up to a few gigahertz can be measured directly and compared with a calibrated frequency standard, derived from the cesium clock, which is still the primary frequency standard [1316]. For higher frequencies a heterodyne technique is used, where the unknown frequency Vx is mixed with an appropriate multiple tmvr of the reference frequency vr (m = 1,2, 3,...). The integer m is chosen such that the difference frequency Av = - tmvr at the output... 

Because of their capability to separate very closely spaced and narrow spectral features (down to a few megahertz with high-finesse devices), FP etalons and interferometers are often used in high-resolution spectroscopy. Such devices are common tools for the analysis of laser radiation, for example (i) to determine the line width of a laser source, (ii) to characterize the mode composition or to ascertain that it is operating in a single longitudinal mode, or (iii) to provide an accurate, calibrated frequency scale when a laser is scanned in wavelength. The radiation analysed by the FP device is coupled to it either in collimated or focused beams. 

The user needs to quantify die calibration frequency based on its application for getting better results. The user can minimize their risk of sub-optimal selection, installation, and maintenance by working with suppliers who can bring to bear substantial measurement expertise and experience, and strong local technical support [7]. 

The same criteria that are applicable in the laboratory can be used for the on-line analysis. In the model-building step, it is important to tolerance the model however, the level of calibration for accuracy and precision and the frequency of recalibration all need to be addressed on an application-by-application basis. As in all modeling situations, it is important that the model be adequate for the questions being raised (see Chapter 7 and the earlier Section II.B for further information). For all process applications, it is desirable to minimize calibration frequency because time calibrating the analyzer is, for all intents and purposes, time lost. Calibration of a dispersive Raman spectrometer is discussed in detail in Chapters 3 and 6 and thus it will only be briefly mention here. The major concern in the trial phase revolves around environmental issues such as temperature and vibration. If the analyzer is being installed in a control room, then a process-hardened analyzer is not necessarily needed. If, however, the analyzer is being installed on or near the plant floor, then it is essential to use a hardened analyzer. If not, then a significant amount of time can be taken up only to discover that laboratory analyzers are not as environmentally... 

Application procedures (including method of calibration), frequency and amount, with appropriate units, and the reason for the meth of application ... 

Calibration instability in the detector is typically caused by dark current changes over time and temperature as well as cutoff wavelength shifts with temperature which can cause small changes in apparent responsivity. Instability in the ROIC is primarily limited to offset changes in MOSFETs over time, temperature, and environmental exposure. The extent to which these impact the calibration frequency of a system is often determined through test and validation of the ROIC at the sensor-chip level, and can take minutes to days of data collection depending on the needs of the application. 

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