Level detector, operational amplifier

Three types are used. (I) Barrier-layer cells. These are satisfactory only for simple filter instruments. (2) Vacuum phototubes. These tubes require an external power supply, unlike barrier-layer cells, and their output is usually amplified before measurement. (3) Photomultiplier tubes are easily the most satisfactory detectors for use in flame photometry. The photocurrent is amplified inside the tube in such a way that much lower light levels can be detected and measured accurately than is possible with vacuum phototubes with amplifiers. A stable source of high voltage up to perhaps 2000 volts is required to operate the photomultiplier tubes, but these tubes are almost universally used in high-performance instruments and are essential if the advantages of using narrow band width are to be obtained. 

The high-voltage power supply, amplifier-discriminator, and scalers were homebuilt (5, 7). During the operation of the detector, propane counting gas was mixed with the helium carrier gas in a 4 1 ratio, and the total combined helium and propane flow rate was maintained at 125 cm min" (NTP). With 2 in. of lead shielding, the typical counter background level was 100-200 cpm. 

Attenuator "A" attenuates the laser-beam power to the appropriate level which is allowed by the MCT detector (<0,5 mW). The optical signal scattered back from the target is collected by the same telescope that was transmittin the laser beam. This weak optical signal is introduced into the laser by the same mirrors and the same "S" beamsplitter, that were used in the transmission process. Inside the laser cavity this low intensity radiation is amplified in the same cavity mode in which the laser is operating. For this reason the mode of the received radiation is identical with local beam mode. This identity secures the best mixiflg efficiency for the heterodyne detection. This mode identity is the reason that we called our system self aligning The lens in front of the detector serves to fit the spot size of the local and amplified (received) beams to the detector size. 

Figure 7.18 The input MOSFET of the direct injection (DI) unit cell holds the detector voltage bias nearly constant, providing high linearity. Addition of the inverting amplifier allows the DI to operate at lower input signal levels withont de-biasing the detector.

The two safety rods and the coarse control rod are each worth approximately 1.3 percent reactivity. The fine control rod, fuel loaded, is worth about 0.3 percent. The neutron flux is monitored by three detectors two BF3 ionization chambers and one BF3 proportional counter, all of which are located in the water tank just outside the lead shield. The detectors are connected respectively to a logarithmic micromicroammeter, a linear micro-microammeter, and a pulse amplifier and count rate meter located on the reactor console. Each indicator is connected through a sensitrol relay to a scram circuit. Additional safety interlocks provide for reactor shutdown if the level of the shield water drops, if the reactor temperature falls below 16 C, or if an earthquake occurs. Sequential interlocks are also present to ensure that the proper operational method is followed. 

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