Contact plates

Electrical Connections. Electric current is brought from the transformers by air-cooled copper busbars and close to the electrode by water-cooled bus tubes and flexible cables, connecting to water-cooled copper contact plates at the electrode. The plates are held against the electrode by hydraulic pressure. The connectors are as short and as balanced as possible to allow cancelling of magnetic fields associated with individual conductors. 

Carbon Electrodes. Carbon electrodes are rigid carbonaceous shapes deployed in electric furnaces. They are the final link in the chain of conductors from the energy source to the reaction zone of an electrically heated vessel. The gap bridged by the electrode is that between the contact plates that transmit current to the electrode and the discharge area at the arc end of the electrode. 

Self-baked carbon electrodes are those whose shapes are formed in situ (33). The carbonaceous mixture is placed into a hoUow tube-shaped metal casing. The upper end receives the unbaked mixture as a soHd block, small particles, or warm plastic paste. The casing contains inwardly-projecting longitudinal perforated fins that become surrounded by baked carbon as the casing is incrementally moved downward and through the contact plates. Casing and carbon are consumed in this furnace. 

Ah.soi ption. Sec. 4, Thermodynamics and Sec. 18, Liquid Gas Systems. For plate columns, see Sec. 18, Gas-Liquid Contacting Plate Columns. For packed columns, see Sec. 18, Gas-Liquid Contacting Packed Columns. ... 

Nishannon A. Pokja M.S. (1977) Comparative studies ofmicrohial contamination of surfaces hy the contact plate and swab methods. 7,4/7/)/ Bacterial, 42, 53-63. 

Fig. 3.14 Left. NASA Mars-Exploration-Rover (artist view courtesy NASA, JPL, Cornell). On the front side of the Rover the robotic arm carrying the Mossbauer spectrometer and other instruments can be seen in stowed position. Right, robotic arm before placement on soil target at Victoria crater rim, Meridian Planum, Mars. The Mossbauer instrument MIMOS II with its circular contact plate can be seen, pointing towards the rover camera. See also Sect. 8.3...

Fig. 3.15 Left External view of the MIMOS II sensor head (SH) with pyramid structure and contact ring assembly In front of the Instrument detector system. The diameter of the one Euro coin is 23 mm the outer diameter of the contact-ring is 30 mm, the inner diameter is 16 mm defining the field of view of the Instrument. Right. Mimos II SH (without contact plate assembly) with dust cover taken off to show the SH Interior. At the front, the end of the cylindrical collimator (with 4.5 mm diameter bore hole) Is surrounded by the four SI-PIN detectors that detect the radiation re-emltted by the sample. The metal case of the upper detector is opened to show its associated electronics. The electronics for all four detectors Is the same. The Mossbauer drive is inside (in the center) of this arrangement (see also Fig. 3.16), and the reference channel is located on the back side In the metal box shown In the photograph...

Adjustable Workbench (PAW) instrument assembly. The SH shown in Figs. 3.15 and 3.16 contains the electromechanical transducer (mounted in the center), the main and reference Co/Rh sources, multilayered radiation shields, detectors and their preamplifiers and main (linear) amplifiers, and a contact plate and sensor. The contact plate and contact sensor are used in conjunction with the IDD to apply a small preload when it places the SH holding it firmly against the target. The electronics board contains power supplies/conditioners, the dedicated CPU, different kinds of memory, firmware, and associated circuitry for instrument control and data processing. The SH of the miniaturized Mossbauer spectrometer MIMOS II has the dimensions (5 x 5.5 x 9.5) cm and weighs only ca. 400 g. Both 14.4 keV y-rays and 6.4 keV Fe X-rays are detected simultaneously by four Si-PIN diodes. The mass of the electronics board is about 90 g [36],... 

MIMOS II has three temperature sensors one on the electronics board and two on the SH. One temperature sensor in the SH is mounted near the internal reference absorber, and the measured temperature is associated with the reference absorber and the internal volume of the SH. The other sensor is mounted outside the SH at the contact ring assembly. It gives the approximate analysis temperature for the sample on the Martian surface. This temperature is used to route the Mossbauer data to the different temperature intervals (maximum of 13, with the temperature width software selectable) assigned in memory areas. Shown in Fig. 3.21 are the data of the three temperature sensors taken on Mars (rover Opportunity at Meridiani Planum) in January 2004 between 12 10 PM on Sol 10 (10 Martian days after landing) and 11 30 AM on Sol 11. The temperature of the electronics board inside the rover is much higher than the temperatures inside the SH and the contact plate sensor, which are nearly identical and at ambient Martian temperature. 

Fig. 3.21 Example of temperature variation as measured by MIMOS II temperature sensors on MER (i) inside the rover body at MIMOS electronics board (black curve), (ii) outside the rover, at the MIMOS II SH (green and red curves), which is at ambient Martian temperature (a) inside the sensor-head, at the reference absorber position (green), (b) outside the SH at the sample s contact plate (red). Temperatures at the two SH positions are nearly identical (difference less than 2 K). During data transmission between the rover and the Earth (or the relay satellite in Mars orbit) the instrument is switched off resulting in immediate small but noticeable temperature changes (see figure above)...

Fig. 8.28 External view of the MIMOS II sensor head without contact plate assembly (left) MIMOS II sensor head mounted on the robotic arm (IDD) of the Mars Exploration Rover. The IDD also carries the a-Particle-X-ray Spectrometer APXS, also from Mainz, Germany, for elemental analysis, the Microscope Imager MI for high resolution microscopic pictures ( 30 pm per pixel), and the RAT for sample preparation (brushing grinding drilling (< 1 cm depth)). Picture taken at Kennedy-Space-Center KSC, Florida, USA...

Fig. 8.29 The flight unit of the MEMOS II Mossbauer spectrometer sensor head (for the rover Opportunity), with the circular contact plate assembly (front side). The circular opening in the contact plate has a diameter of 15 mm, defining the field of view of the instrument...

Grade Air Sample (cfu/m ) Settle Plate, Diameter 90 mm (cfu/4 h) Contact Plate, Diameter 55 mm (cfu/plate) Personnel Glove Print, 5 fingers (cfu/glove)... 

Contact plate areas vary from 24 to 30 cm. When swabbing is used in sampling, the area covered should be greater than or equal to 24 cm but no larger than 30 cm. ... 

The use of contact plates is the recommended technique. The RODAC plate method is the simplest, but it is useful only for flat surfaces. Swab samples afford examination of corners, crevices, and other area inaccessible to RODAC plates. 

Two days before testing incubate in inverted position a sufficient number of RODAC plates (or contact plates), swabs, agar strips, and plates for fingerprints. 

To minimize disruptions to critical operations, surface sampling should be performed at the stop or the end of operations. Surface sampling may be accomplished by the use of contact plates or by the swabbing method. 

Contact plates are used when sampling regular or flat surfaces. The test is performed with RODAC (replicate organisms detecting and counting) plates, or contact plates, where the convex agar surface rises above the brim of the plate. 

Count the number of microbial colonies on each plate. The microbial estimates are reported per contact plate or per swab. Examine the types of colonies and submit the representative colonies for identification. Mold does not carry special status relative to bacteria. Any significant shifts in type or number require action — regardless of mold vs. bacteria. 

Sampling contact plates and swabs shall be used. 

Surface air system sampler. This integrated unit consists of an entry section that accommodates an agar contact plate. Immediately behind the contact plate is a motor and turbine that pull air through the unit s perforated cover over the agar contact plate and beyond the motor, where it is exhausted. Multiple mounted assemblies are also available. 

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