Pressure measurement flow errors

Flow Low mass flow indicated. Mass flow error. Transmitter zero shift. Measurement is high. Measurement error. Liquid droplets in gas. Static pressure change in gas. Free water in fluid. Pulsation in flow. Non-standard pipe runs. Install demister upstream heat gas upstream of sensor. Add pressure recording pen. Mount transmitter above taps. Add process pulsation damper. Estimate limits of error. 

The best method of determining the minimum fluidization velocity umf is experimentally, by measuring the pressure drop across the bed over a range of fluid velocities. The pressure drop increases linearly until fluidization occurs and then increases very slowly indeed up to about twice the minimum fluidization velocity the pressure drop may appear to be constant within experimental error. When a bed is initially fluidized, there is a tendency for the pressure drop across the bed to be rather high and to go through a peak as incipient fluidization occurs. It is possible that this is caused by a need to unstick the particles. If the fluid velocity of an already fluidized bed is reduced, the peak in the pressure drop is not observed and a much clearer transition to the linear pressure drop—flow... 

The Bayard-Alpert system with modulator (see Fig. 3.16 d), introduced by Redhead, offers pressure measurement in which errors due to X-ray and ion desorption effects can be quantitatively taken into account. In this arrangement there is a second thin wire, the modulator, near the anode in addition to the ion collector inside the anode. If this modulator is set at the anode potential, it does not influence the measurement. If, on the other hand, the same potential is applied to the modulator as that on the ion collector, part of the ion current formed flows to the modulator and the current that flows to the ion collector becomes smaller. The indicated pressure p, of the ionization gauge with modulator set to the anode potential consists of the portion due to the gas pressure pg and that due to the X-ray effect pg ... 

Thermal flowmeters are mostly used in gas services, but can also detect liquid flows. They can measure flows from 0 to 10,000 kg/h (22,000 lb/h) with 1 to 2% FS errors. Their rangeability is from 10 1 to 100 1, their operating temperature range is up to 500°C (950°F), and they can operate at pressures from atmospheric to 83 bar (1,200 psig). 

The model describes, within the limits of measuring error, the experimental temperature and concentration profiles quite well over a wide temperature range (more than 100 C) and propylene conversion range (Table I), (Figures 2 - 4). But the reaction orders for propylene and oxygen have only a limited reliability since especially the oxygen concentration along the reactor varied only within narrow limits. Additionally, pressure and flow rate were, for the most part, held constant (Table I). 

The value of the coefficient of discharge Cd for orifice meters depends on the properties of the flow system, the ratio of the orifice diameter to the upstream diameter, and the location of the pressure-measuring taps. Values of Cd for sharp-edged orifice meters are presented in Fig. 14-55. These values apply strictly for pipe orifices with throat taps, in which the downstream pressure tap is located one-third of one pipe diameter from the downstream side of the orifice plate and the upstream tap is located one pipe diameter from the upstream side. However, within an error of about 5 percent, the values of Cd indicated in Fig. 14-55 may be used for manometer taps located anywhere between the orifice plate and the hypothetical throat taps. 

Tests are conducted to determine capacity, heat transfer rates, steam economy, product losses, and cleaning cycles. Practically all the criteria of evaporator performance are obtained from differences between test measurements. Errors can result when measuring flow rates, temperatures and pressures, concentrations, and steam quality. Factors which can have a great effect on performance include dilution, vent losses, heat losses, and physical properties of fluids. 

The pressure derivatives found from equation (18.50) for Prior Transient Integration and (18.54) for Extended Prior Transient Integration were integrated using the Euler method. In each case the error was measured in terms of the sum of the squared flow errors, E, at time to ... 

The sum of the squared flow errors is a sensitive measure of error, especially in the vicinity of flow reversal. Table 18.4 compares the values of the intermediate pressures p2 and p found from integration... 

In Chapter 1, the rales of nomenclature are reviewed— units of physical quantities, abbreviations, conversion between SI and British Units— and the various national and international standards bureaus are mentioned. Chapter 2 introduces significant figures and concepts of accuracy, precision and error analysis. Experimental planning is discussed in some detail in Chapter 3. This subject is enormous and we try to distil the essential elements to be able to use the techniques. Chapters 4 and 5 cover many aspects of measuring pressure and temperature. The industrial context is often cited to provide the student with a picture of the importance of these measurements and some of the issues with making adequate measurements. Flow measurement instrumentation is the subject of Chapter 6. A detailed list of the pros and cons of most commercial... 

Lord Kelvin stated that to measure is to know (Unnamed 2011). In fact, it would be more precise to say that to measure is to know... better. Almost all measurements have errors with respect to their absolute value, be it temperature, pressure, flow rate, or any of several other standard measurements necessary to evaluate a phenomenon, characterize an instrument, or run a chemical plant. Error is deflned as the absolute or relative difference between the measured value and the true value as measured by a recognized standard. Note that the term recognized standard is mentioned, and not true value since the true value can rarely, if ever, be known exactly. 

To compare the elemental distribution ratio betweoi the condoised zinc and the matte from the different tests, these were also normalized to Pzn = 0.1 atm for all tests by assuming (normalized distribution ratio at 0.1 atm zinc partial pressure) = (measured distribution ratio Pzn / 0.1) as listed in Table IV. In general, the scatter of the estimated distribution ratio is large. This is not surprising if we recognize the many sources of variation different temperatures, different degrees of splashing caused by different feed rates and gas flow rates, aiuilytical errors and even different matte compositions. 

After calibration was measured between the flow velocity and fluorescence intensity, flow velocity profile in a pressure-driven flow was measured. The measured flow velocity profile within the submicrocapiUary and comparison with theoretical prediction based on the Hagen-Poiseuille equation is shown in Fig. 4a, where rectangular dots represent the average velocity of the measurement point. The standard deviatimi error bars are also shown in Fig. 4a. The difference between the experimental data and... 

In many industrial control problems, notably those involving temperature, pressure, and flow control, measurements of the controlled variable are available, and the manipulated variable is adjusted via a control valve. In feedback control, corrective action is taken regardless of the source of the disturbance. Its chief drawback is that no corrective action is taken until after the controlled variable deviates from the set point. Feedback control may also result in undesirable oscillations in the controlled variable if the controller is not tuned properly, that is, if the adjustable controller parameters are not set at appropriate values. The tuning of the controller can be aided by using a mathematical model of the dynamic process, although an experienced control engineer can use trial-and-error tuning to achieve satisfactory performance in many cases. Next, we discuss the two types of controllers used in most commercial applications. 

We shall further suppose that any type of measurement can be characterised, besides the proper measurement of flow or level, also by several other parameters. In addition, there must be defined also units of primary data measurement and functions for calculation of the balanced quantity on the basis of the flowmeter reading, pressure, temperature and the like. The type of measurement must also comprise information on measurement error, used in reconciliation of redundant data and detection of possible measurement gross errors. 

I could write a whole book just about making pressure and flow and level and temperature measurements in the field. Actually, 1 have. Troubleshooting Process Operations, 3d ed., Pennwell Publications, Tulsa, Oklahoma.) But I ve made my point. Making field measurements is complicated. There are too many variables to turn the job over to the outside unit operator. There are so many sources of potential error to consider and eliminate. There is only one way to make sure any job is done right and that s to do it yourself. At least you will know which data are reliable and which data are questionable. 

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