Chart recorders

Usually all the flaw detectors in service have two channels to detect defects of a rope the LMA and LF channels. The inspection information is recorded by a chart recorder or by a tape recorder. 

The detector must be sensitive to the radiation falling on it, and the spectrum is very often displayed on a chart recorder. The spectrum may be a plot of absorbance or percentage transmittance (IOO///0 see Equation 2.16) as a function of frequency or wavenumber displayed linearly along the chart paper. Wavelength is not normally used because, unlike frequency and wavenumber, it is not proportional to energy. Wavelength relates to the optics rather than the spectroscopy of the experiment. 

In addition, most devices provide operator control of settings for temperature and/or response slope, isopotential point, zero or standardization, and function (pH, mV, or monovalent—bivalent cation—anion). Microprocessors are incorporated in advanced-design meters to faciHtate caHbration, calculation of measurement parameters, and automatic temperature compensation. Furthermore, pH meters are provided with output connectors for continuous readout via a strip-chart recorder and often with binary-coded decimal output for computer interconnections or connection to a printer. Although the accuracy of the measurement is not increased by the use of a recorder, the readabiHty of the displayed pH (on analogue models) can be expanded, and recording provides a permanent record and also information on response and equiHbrium times during measurement (5). 

Continuous monitors usuaUy indicate the pollutant concentration on both an indicator and a chart recording. This provides a visual indication of the instantaneous emissions, along with a permanent record of the quantitative emissions over a period of time. The monitoring system may also be equipped with an alarm device to signal the operator if the allowable emission level is being exceeded. Data-logging systems coupled with micropro-... 

For the standby pump start test, which is an important test to ensure the pumps transfer without large pressure swings, a check should be made to see if the relief valves lift or the pressure falls to a pressure one half the difference between the standby pump start pressure and the compressor trip pressure. The transient pressure is best measured with a multipen chart recorder. The chart speed must be high enough to fully display the pressure variation. While not as good as the chart recorder, a simple shop-made test setup can be substituted. A spare switch is temporarily connected to the same location as the other switches. This switch is calibrated to close at the threshold acceptance pressure. The contacts are wired to a test light through a seal relay. The purpose of the relay is to maintain the cir-... 

If you cannot select suitable equipment for your current environment, you may need to control the environment in order to carry out the measurements. In such areas the environmental factors important to maintaining stable measurement should be monitored and the monitoring equipment calibrated. Chart recorders enable you to monitor conditions without having to be in constant attendance. The environment should be controlled in areas where calibration is carried out in order to provide stable conditions in which accurate and precise measurement can be taken. However, some modern equipment is so stable that environmental controls are unnecessary except in special circumstances. 

The first set of case studies illustrates errors due to the inadequate design of the human-machine interface (HMI). The HMI is the boundary across which information is transmitted between the process and the plant worker. In the context of process control, the HMI may consist of analog displays such as chart records and dials, or modem video display unit (VDU) based control systems. Besides display elements, the HMI also includes controls such as buttons and switches, or devices such as trackballs in the case of computer controlled systems. The concept of the HMI can also be extended to include all means of conveying information to the worker, including the labeling of control equipment components and chemical containers. Further discussion regarding the HMI is provided in Chapter 2. This section contains examples of deficiencies in the display of process information, in various forms of labeling, and the use of inappropriate instrumentation scales. 

As described earlier, in the first stage of perception, information is acquired via the senses from a number of sources. These may include gauges and chart recorders, VDU screens in a control room, verbal communication with individuals on the plant, or direct observation of process variables. In the short term, this information provides feedback with regard to specific control actions. 

Scan information sources (dials, chart recorders, etc.). If the pattern of indicators is very familiar, the worker will probably immediately branch to the Execute Actions box (via the thin arrow) and make the usual response to this situation (e.g., pressing the alarm accept button if the indications suggest a nonsignificant event). 

The term control panel refers to the instrumentation console in a central control room through which process information is communicated to the process worker and via which the worker changes the state of the process. This category includes display elements such as chart recorders, bar indicators, dials, and modem VDU-based systems together with control elements such as buttons, switches, track balls and mice. The control panel is the human-machine interface (see Chapter 2) that has traditionally received the most attention from human factors specialists. 

Indications such as VDU displays, meters, and chart recorders available in the control room or on the plant that are associated with the various causes and consequences... 

The whole range of error types that could occur at each task step are described in Figure 4.16. The terms action errors and checking errors are self-explanatory. Retrieval errors refer to the retrieval of infonnation either from an external source (e.g., a chart recorder or a procedure) or from memory. Transmission/ communication errors refer to communications among individuals either directly or via written communications. Selection/choice errors refer to making incorrect choices among alternative operations, for example, manual instead of automatic. 

The determination of the tangents on the chart strip is difficult, as even little mistakes lead to significant deviations in the calculated N. This fact and the disappearance of the chart recorders in modern GPC units indicate another characterization procedure. 

There are many industrial applications in which permanent records (extending over long periods of time) of the instrument readings are required. Chart recorders of various forms are available for this purpose. The most common general-purpose unit is the digital strip chart recorder, in which the input signal is used to drive the movement of a recording arm that passes over a paper chart in the y-direction. At the same time, the chart is... 

Fig. 9.1 (a) Block diagram of a gas chromatograph. (b) Typical chart record. Reproduced by permission from R. C. Denney, The Truth about Breath Tests, Nelson, London, 1970. 

A number of commercial titrators are available in which the electrical measuring unit is coupled to a chart recorder to produce directly a titration curve, and by linking the delivery of titrant from the burette to the movement of the recorder chart, an auto-titrator is produced. It is possible to stop the delivery of the titrant when the indicator electrode attains the potential corresponding to the equivalence point of the particular titration this is a feature of some importance when a number of repetitive titrations have to be performed. Many such instruments are controlled by a microprocessor so that the whole titration procedure is, to a large extent, automated. In addition to the normal titration curve, such instruments will also plot the first-derivative curve (AE/AV), the second-derivative curve (A2 E/AV2), and will provide a Gran s plot (Section 15.18). 

Commercial polarographs are also available in which the voltage scan is carried out automatically while a chart recorder plots the current-voltage curve. A counter-current control is incorporated which applies a small opposing current to the cell which can be adjusted to compensate for the residual current this leads to polarograms which are better defined. Most of these instruments also incorporate circuits which permit the performance of alternative, more sensitive types of polarography as discussed in Section 16.9... 

The following experiments (Section 16.14-16.16), which can well be performed with a manual polarograph, serve to illustrate the general procedure to be followed in d.c. polarography it is advantageous to use a chart recorder to produce the polarogram. 

Make the connections to the polarographic analyser and adjust the applied voltage to —0.8 V, i.e. a value well in excess of the deposition potential of lead ions. Set the stirrer in motion noting the setting of the speed controller, and after 15-20 seconds, switch on the electrolysis current and at the same time start a stopclock allow electrolysis to proceed for 5 minutes. On completion of the electrolysis time, turn off the stirrer, but leave the electrolysis potential applied to the cell. After 30 seconds to allow the liquid to become quiescent, replace the electrolysis current by the pulsed stripping potential and set the chart recorder in motion. When the lead peak at ca 0.5 V has been passed, turn... 

Visual methods have been virtually displaced for most determinations by methods depending upon the use of photoelectric cells (filter photometers or absorptiometers, and spectrophotometers), thus leading to reduction of the experimental errors of colorimetric determinations. The so-called photoelectric colorimeter is a comparatively inexpensive instrument, and should be available in every laboratory. The use of spectrophotometers has enabled determinations to be extended into the ultraviolet region of the spectrum, whilst the use of chart recorders means that the analyst is not limited to working at a single fixed wavelength. 

The more advanced spectrofluorimeters are capable of automatically scanning fluorescent spectra between about 200 and 900 nm and produce a chart record of the spectrum obtained. These can also operate at a fixed wavelength and are equally suitable for carrying out quantitative work their main application tends to be for the detection and determination of small concentrations of organic substances. 

All infrared spectrophotometers are provided with chart recorders which will present the complete infrared spectrum on a single continuous sheet, usually with wavelength and wavenumber scales shown for the abscissa and with absorbance and percentage transmittance as the ordinates. More advanced instruments also possess visual display units on which the spectra can be displayed as they are recorded and on which they can be compared with earlier spectra previously obtained or with spectra drawn from an extensive library held in a computer memory. These modern developments have all led to quantitative infrared spectrophotometry being a much more viable and useful analytical procedure than it was just a few years ago. 

The read-out systems available include meters, chart recorders, and digital display meters have now been virtually superseded by the alternative methods of data presentation. 

An interesting description of a commercial tin-plate installation appears in a special issue of the Norelco Reporter Each side of the coated steel strip can be traversed continuously by a separate measuring head, and the results appear on a two-pen strip-chart recorder located near the 4 x 2 x 9-foot dual electronic rack that energizes and regulates the two measuring heads some 100 feet away. 

An example of the usefulness of x-ray emission spectrography for qualitative trace analysis is shown in Figure 7-1, which contains a chart recording made in the authors laboratory of the emission spectrum from a genuine bank note. 

Fig. 7—1. Chart recording of the emission spectrum from a genuine bank note.

A chart recording for a typical alloy appears in Figure 7-4. Of the peaks shown, those of tungsten (traceable to the x-ray tube) and of manganese (not measured) may be ignored here. 

Fig. 7-4. Chart recording from x-ray spectrograph for high-temperature ailoy typical of Tables 7-4 and 7-5. The numbers above selected peaks indicate approximate line intensity expressed as counts per second. (Courtesy of Rrissey, Anal. Chem., 25, 190.)...

Step 1. Estimate the concentration of the element from a chart recording of the sample or by optical spectroscopic observation. 

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