Speed probes

It is particularly necessary to measure the speed of rotation of the decanter bo wl and the gearbox pinion shaft. Occasionally a tachometer will be built into the braking device. More generally, bowl and pinion speeds are measured by proximity probes, acting on a protuberance or castellation, on a spigot, hub or shaft. 

The speeds of the feed and polymer pump, and also the cake sample pump, are useful though not absolutely necessary to measure, as comparing this speed with a calibration speed will indicate the onset of wear. 

Measuring the speed of the polymer screw feeder has already been mentioned. 

Another useful speed monitor w ould be on the solids conveyor driven shaft. All that is needed here is an indication that the shaft has stopped, for instance if the belt should break. In a non-attended plant it is essential to know if the off-take system ceases to function, so that the feed may be arrested. 

It is worth noting that the majority of downtime of a decanter plant is caused by failures in ancillary equipment, rather than the decanter itself. 

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Nier AO (1996) Planetary atmospheres with mass spectrometers carried on high speed probes or satellites. Rarefied gas dynamics. Progress in Astronautics and Aeronautics 51 1255-1275. 

At still shorter time scales other techniques can be used to detenuiue excited-state lifetimes, but perhaps not as precisely. Streak cameras can be used to measure faster changes in light intensity. Probably the most iisellil teclmiques are pump-probe methods where one intense laser pulse is used to excite a sample and a weaker pulse, delayed by a known amount of time, is used to probe changes in absorption or other properties caused by the excitation. At short time scales the delay is readily adjusted by varying the path length travelled by the beams, letting the speed of light set the delay. 

Disadvantages. The magic angle must be extremely stable and accurately set. The spiiming speed must show good stability over the duration of the experiment. The probe needs to be accurately tuned and careful correction for irradiation and detection variations with frequency, and baseline effects are necessary. The gain... 

The detector D monitors the absorption of the probe beam as a function of the delay between the pulses given by xHc, where c is the speed of light and v is the difference between the optical path travelled by the probe and by the pump pulse. Adapted from [110],... 

Figure C3.5.3. Schematic diagram of apparatus used for (a) IR pump-probe or vibrational echo spectroscopy by Payer and co-workers [50] and (b) IR-Raman spectroscopy by Dlott and co-workers [39]. Key OPA = optical parametric amplifier PEL = free-electron laser MOD = high speed optical modulator PMT = photomultiplier OMA = optical multichannel analyser.

It turns out that in low-viscosity blending the acdual result does depend upon the measuring technique used to measure blend time. Two common techniques, wliich do not exhaust the possibilities in reported studies, are to use an acid-base indicator and inject an acid or base into the system that will result in a color change. One can also put a dye into the tank and measure the time for color to arrive at uniformity. Another system is to put in a conductivity probe and injecl a salt or other electrolyte into the system. With any given impeller type at constant power, the circulation time will increase with the D/T ratio of the impeller. Figure 18-18 shows that both circulation time and blend time decrease as D/T increases. The same is true for impeller speed. As impeller speed is increased with any impeller, blend time and circulation time are decreased (Fig. 18-19). 

Expander-compressor shafts are preferably designed to operate below the first lateral critical speed and torsional resonance. A flame-plated band of aluminum alloy or similarly suitable material is generally applied to the shaft in the area sensed by the vibration probes to preclude erroneous electrical runout readings. This technique has been used on hundreds of expanders, steam turbines, and other turbomachines with complete success. Unless integral with the shaft, expander wheels (disks) are often attached to the shaft on a special tapered profile, with dowel-type keys and keyways. The latter design attempts to avoid the stress concentrations occasionally associated with splines and conventional keyways. It also reduces the cost of manufacture. When used, wheels are sometimes secured to the tapered ends of the shaft by a common center stretch rod which is pre-stressed during assembly. This results in a constant preload on each wheel to ensure proper contact between wheels and shaft at the anticipated extremes of temperature and speed. 

The limits expressed in Table 7-3 (x-axis = operating speed in rpm, y-axis = overall vibration level in mils [peak to peak]) are based on experienee in refineries. The guide refleets the typieal proximity probe installation elose to and supported by the bearing housing and assumes the main vibration eomponent to be of [lx rpm] frequeney. The... 

Figure 4-6 is an amplitude-speed eurve showing the loeation of the running speed to the eritieal speed, and the amplitude inerease near the eritieal speed. When the rotor amplifieation faetor, as measured at the vibration probe, is greater than or equal to 2.5, that frequeney is ealled eritieal and the eorresponding shaft rotational frequeney is ealled a eritieal speed. For the purposes of this standard, a eritieally damped system is one in whieh the amplifieation faetor is less than 2.5. 

The damped (unbalance response) plots are not really very impressive, but they address the information every operator would like to see. Amplitude is plotted against speed at various stations such as at the probes (see... 

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