Vacuum measurement

Vacuum measurement spans the range from 10 Pa (atmospheric pressure) to pressures that are less than 10 orders of magnitude. Sub atmospheric pressures are divided into six regions for convenience (9) ... 

Hot-Cathode Ionization Gauges. For pressures below approximately lO " Pa, it is not possible, except under carehiUy controlled conditions, to detect the minute forces that result from the coUision of gas molecules with a soHd wall. The operation of the ion gauge is based on ionisa tion of gas molecules as a result of coUisions with electrons. These ions are then subsequendy collected by an ion collector. Ionisa tion gauges, used almost exclusively for pressure measurement in high, very high, ultrahigh, and extreme ultrahigh vacuums, measure molecular density or particle dux, not pressure itself. 

Figure 1. Shown here is a vacuum measurement installation.

O When cakes tend to crack under vacuum measures such as a fiapper, compression blanket or pressure roll may assist in sealing the cracks thus avoiding loss of vacuum. When such measures are used it is necessary to make sure that the belt supporting system can take these extra vertical loads. 

When cakes tend to crack under vacuum measures, such as a flapper or pressure roll may assist in sealing the cracks thus avoiding loss of vacuum. 

For reference, note that unit of vacuum measurement is the torr. 

Fig. 4.22. Reaction cell 1 - ZnO sensor 2 - evaporator of silver atoms 3 shutter used to terminate the beam of Ag atoms 4 - collimating apertures 5 an aperture used for pumping the cell out 6 - magnet 7 - magnetic drive for a shutter 8 - getter 9 — vacuum-measuring tube iO, 11 - electrodes 12 - thermocouple.

Pressure loss coefficient, 13 261 Pressure measurement, 11 783 20 644-665. See also Vacuum measurement electronic sensors, 20 651-657 mechanical gauges, 20 646-651 smart pressure transmitters, 20 663-665 terms related to, 20 644-646 Pressure measurement devices. See also Pressure meters Pressure sensors location of, 20 682 types of, 20 681-682 Pressure meters, 20 651 Pressure microfiltration/ultrafiltration,... 

At the end of the 8-h test, vacuum measurements in the three monitor wells had stabilized (for at least 2 h) with the following recorded readings ... 

In vacuum measurement systems used in the high and ulfrahigh regimes it... 

Capacitive pressure transducers are traditionally used for relatively low pressure ranges (up to about 800 kPa) and for vacuum measurement (Section 6.3.5). 

Elastic elements such as diaphragms and capsules are used as sensing elements in combination with different displacement transducers (e.g. inductive, potentiometric, etc.) for low/medium vacuum measurements down to about 1 torr. Elastic elements have been employed in conjunction with capacitive transducers for the measurement of pressures as low as 10 5 torr. 

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