Automatic calibration, balances

A modern electronic analytical balance provides unprecedented speed and ease of use. For example, one instrument is controlled by touching a single bar at various positions along its length. One position on the bar turns the instrument on or off, another automatically calibrates the balance again.st a standard mass or pair of masses, and a third zeros the display, either with or without an object on the pan. Reliable mass measurements are obtainable with little or no instruction or practice. 

The force of gravity varies from location to location and at different elevations above Earth s surface. To compensate for the unknown local gravitational force, an internal calibration mass at the upper left in Figure 2-4 is required. In the automatic calibration step, the balance measures how much current is required to balance the known mass. The same factor is then applied to the weighing of unknown masses. 

A calibration schedule details the calibration of balances, volumetric glassware, automatic pipettes, thermometers, pH and conductivity meters, wavelength and photometric scales etc. The schedule consists of periodic external checks, employing a suitably accredited calibration service, supported by more regular in-house performance checks. 

Undefined delay times and distortion of the rise time reduce the derivable information of waveform analysis but the end-tidal value and the average value can be used clinically. Figure 23-24 presents an example of a flow mismatch with distortion of the CO waveform. The inspiratory value may be used to detect system failures. During the warm-up time and the subsequent Hrst hour, (he IR sensor typically shows increased drift and reduced accuracy until temperature balance is reached. Zero-point calibration can be effected periodically by automatically aspirating ambient air. Drifts of the measuring system are calibrated manually or automatically over longer periods by use of test gases. 

Because density is often used as a quality control check, particularly on batches of rubber compound, there has been a necessity to make measurements essentially in accordance with standards such as ISO 2781 but making the determinations as rapidly as possible. Hence various designs of "specific gravity balance" arc in existence, primarily intended for rubbers, which to varying degrees automate the process. In one form of apparatus, the practical steps of weighing in air and water are taken, but the result may then be read directly from a scale calibrated in density. Completely automatic apparatus have also been produced. 

Metering can be done either by weight using a balance, or by volume using a calibrated vessel, pipette, disposable syringe or an automatic mixing and metering device. 

All balance types for pharmacy preparation preferably have an automatic internal calibration option and can operate in connection with software functions, e.g. for in-process control. The balance should be equipped with a stability indicator so that the weight is only registered or printed after stabilisation of the balance. Draft shields are important, especially for weighing in controlled (ventilated ) environments. Special functions such as piece counting (for counting tablets or capsules the so-called pill counter ) may be advantageous. 

Figure 2. Analytical balance Mettler AX201,22()gxO.OI ing Automatic self-calibration with built-in reference masses.

In electronic balances the force exercised by the load on the base is measured with a force measurement cell (for example, an electrical strain gauge) and transformed into an electrical signal. This signal is processed within the balance in a digital or analog fashion and is then displayed. These systems can be calibrated and used in fully automatic installations. As force measurement cells one can use pressure sensors with lower requirements for accuracy. These are installations in which the weight is transformed into pressure pneumatically or hydraulically one can determine levels in tanks or reaction vessels by this method, which can also be used to meter automatically the main ingredients of a batch process, for example the water and monomer phase in an emulsion or suspension polymerization. 

It has retained all of its predecessor s features and advantages Precision servo/screw drive, speeds 0.2 to 300 in/min 25 Ibf force capacity Measures Static Peak, Kinetic Peak, Valley, Average and RMS forces Easily switches between English, Metric and SI units Auto-adapts to any power source from 90 to 264 volts, 47 to 63 Hz Variable angle peel fixture standard 180 degree peel, COF hardware standard Embedded mkroprocessor permits self-contained, stand-alone operation Running and lot statistics (Mean, Standard Deviation, Coefficient of Variation) Automatic balance and calibration... 

Calibrate the automatic balance according to manufacturer s instructions. 

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