How Instruments Work

We have discussed the American system inches of mercury (in Hg) in Chap. 6, How Instruments Work. Of more immediate interest is Table 16.1. To do any sort of vacuum calculation, we need to convert to the absolute system, in millimeters of mercury (mm Hg). Unfortunately, we also need to correct measurements made with an American-type, (in Hg) vacuum gauge, for atmospheric pressure. You can interpolate between the two sets of data in Table 16.1, to correct for almost the entire range of typical atmospheric pressures. 

Let us say we have an ordinary orifice-type flowmeter, as shown in Fig. 21.5 (see Chap. 6, How Instruments Work ). What happens if the low pressure (i.e., the downstream) orifice tap plugs Does the indicated flow go up or down ... 

Process Instrumentation is a core class designed to teach the process technology student the basic principles for reading process blueprints, the primary function of instruments, and how instruments work together to automatically control a process. Process instruments fall into five different groups (1) primary elements and sensors, (2) transmitters, (3) controllers, (4) transducers, and (5) final control elements. Figure 2-5 shows various instruments used in the processing industry. 

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