Carbon resistor

Fig. 9.5. The electrical resistance R(T) for some typical thermometers. A-B denotes Allen-Bradley carbon resistor. Speer is a carbon resistor. CG is carbon-in-glass. CX 1050 is a Cernox and RX 202A is a ruthenium oxide from LakeShore. Ge 100 and Ge 1000 are Cryocal germanium thermometers [45]. 

Ge resistors are specifically produced for low-temperature thermometry carbon and Ru02 resistors are commercial products for electronics. Pure carbon is not a semiconductor. The negative slope R(T) is due to the production process which consists in pressing and sinterization of carbon particles with glue. The resulting resistance is probably determined by the contact resistance between the particles. The cost of the carbon resistor thermometer is very low. Manufacturers such as Speer, Allen-Bradley and Matsushita have produced in the past carbon resistors for many years. Most of firms have now ceased manufacture, although their products may still be found in the storerooms of research laboratories. 

Detailed description of carbon resistor is found in some low-temperature text books [2,19,20]. Nowadays, they are usually replaced by thick-film resistors (Ru02), which are also much easier to mount. 

Early bolometers used, as thermometers, thermopiles, based on the thermoelectric effect (see Section 9.4) or Golay cells in which the heat absorbed in a thin metal film is transferred to a small volume of gas the resulting pressure increase moves a mirror in an optical amplifier. A historical review of the development of radiation detectors until 1994 can be found in ref. [59,60], The modern history of infrared bolometers starts with the introduction of the carbon resistor, as both bolometer sensor and absorber, by Boyle and Rogers [12], The device had a number of advantages over the Golay cell such as low cost, simplicity and relatively low heat capacity at low temperatures. 

Nevertheless the heat capacity of a carbon resistor was not so low as that of crystalline materials used later. More important, carbon resistors had an excess noise which limited the bolometer performance. In 1961, Low [61] proposed a bolometer which used a heavily doped Ge thermometer with much improved characteristics. This type of bolometer was rapidly applied to infrared astronomy as well also to laboratory spectroscopy. A further step in the development of bolometers came with improvements in the absorber. In the early superconducting bolometer built by Andrews et al. (1942) [62], the absorber was a blackened metal foil glued to the 7A thermometer. Low s original bolometer [61] was coated with black paint and Coron et al. [63] used a metal foil as substrate for the black-painted absorber. A definite improvement is due to J. Clarke, G. I. Hoffer, P. L. Richards [64] who used a thin low heat capacity dielectric substrate for the metal foil and used a bismuth film absorber instead of the black paint. 

The noise of an actual resistance is always higher than the theoretical limit. While for metal resistors the noise level is close to the theoretical limit, the noise level in carbon resistors is much higher. The resistance of the tunneling junction, which is parallel to the feedback resistor, should be taken into account when its value is comparable to that of the feedback resistor. 

The optimum operating temperature for minimum noise from the FET was found to be slightly higher than the operating temperature of the Ge(Li) detector. A thermal heater made from a 100-ohm carbon resistor was therefore installed next to the FET and operated at a current that heated the transistor to a temperature just above that of liquid nitrogen. 

As was shown in Figure 3.159, cryogenic temperatures can be detected by integrated circuit diodes types K, T, and E thermocouples (TCs) class A and B resistance temperature detectors (RTDs) acoustic and ultrasonic thermometers germanium and carbon resistors and paramagnetic salts. As TCs and RTDs will be discussed in separate subsections, here the focus will be on the other sensors. 

Commercially available carbon resistors have been used as temperature sensors in the cryogenic temperature area near absolute zero, from about -253°C to -272°C (-424°F downward to below -458°F). One major benefit of the carbon resistor at low temperature is its lower susceptibility to adverse effects caused by a magnetic field and stray radio interference. They do require individual calibration to keep the measurement error under 1%. Carbon resistors may be incorporated into resistor networks to improve linearity. These sensors exhibit a large increase in resistance below -253°C ( 424°F). Reproducibility on the order of 0.2% is obtainable when calibrated individually. Small size, low cost, and general availability make their use attractive in cryogenic work. 

Table 9.1 Color Code for Carbon Resistors and Capacitors3...

The experimental details have been reported elsewhere (X, X) Briefly, matrices are formed by codeposition of excess argon with atomic potassium on a sapphire plate mounted inside an ESR cavity which is itself attached to a variable temperature liquid helium dewar. Cluster formation occurs during deposition and is accomplished by warming the sapphire surface above a nominal deposition temperature of 4.2 K. For spectra shown here, temperature measurements were made with a calibrated carbon resistor and are judged accurate to within 5%. 

The simplest circuit based on the carbon material is demonstrated in Fig. 2. It consists of CNT network transistor with a sequentially contacted carbon resistor representing the function of the logic gate. The FET is made of CNT deposited on carbon electrodes. Carbon resistor is made through the LAO of one carbon electrode. 

Where clock-radios (figure 30) are employed, a variety of significant debris may be discovered. The bulk of all radio enclosures are manufactured cither from wood or plastics and these would, therefore, disintegrate in a fire of any magnitude. Most of these radios arc built on a rather heavy steel or aluminum chassis, and various components are often riveted to this metal base. A normal superheterodyne receiver will probably include a double-section variable capacitor having a radier heavy mounting. Carbon resistors or certain metal-encased capacitors may come through the fire reasonably intact. Parts of the clock... 

Multiple reports on the presence of this noise in such a diverse group of systems as carbon resistors, semiconductors, metallic thin films, and aqueous ionic solutions led researchers to believe in the existence of some profound... 

Current noise is the noise component exceeding the thermal noise level. In systems relevant to the present context, i.e., carbon-black-filled polymers, carbon resistors, solutions etc., it normally has a frequency distribution of the form l// , where a = 1-3. The intensity of the noise thus falls rapidly with increasing frequency. The current noise level usually greatly exceeds that of the thermal noise. 

Figure 3 shows the disassembled cryostat its cover, the fittings with which it is installed in the test machine, and the specially constructed dynamic load cell. Not shown is the liquid-level indicator probe, which is of the carbon-resistor type. 

Thermistor and carbon resistor sensors performed satisfactorily, in that no false indication was noted even during the dewar filling operation and during pressurization or depressurization. Recorded response times on emergence were relatively fast. Some manufacturers have installed a separate heater w ire winding around the sensing element to speed up the temperature rise and thereby improve the recovery time. 

The critical temperature measurements were made with g-W, lOO-H Allen Bradley carbon resistors. The carbon resistors were calibrated at Ff = 0 by comparison to a calibrated germanium resistor prior to each testing sequence. The field effect on the carbon resistor calibration was determined from the data of Neuringer and Shapira [ ]. Automatic temperature controllers were used to main-... 

It is fi quently observed that excess l/f noise is related to the microscopic sample structure and to the manufactural technology. This kind of noise is particularly sensitive to the surface and interface defects (Jones 1994). There are manufactural techniques which give small dispersion of the mean characteristic values, such as resistance or currents. On the other hand these devices can exhibit large dispersion ofthe noise characteristics. So, for example, metal thin film resistors have lower l/f noise than granular film resistors made from cermet thick films or carbon resistors. 

The net useful refrigeration capacities of a t5q>ical cooler were determined by measuring the power input to an electrical heater, at various operating pressures. The cold end of the 1/2 in. heat exchanger shown in Fig. 5 was modified to incorporate electrical leads for a small carbon resistor, which was installed... 

Question by J. S. Tyler, AiResearch Manufacturing Co. Is the 4-watt load capability at 1.0 scfm for hydrogen based on the carbon resistor load exclusively ... 

Answer by author The refrigeration capacity referred to in Fig. 8 was the net refrigeration based on the measured electrical heat input to the carbon resistor. It did not include heat leak through leads or through the exchanger, radiation to the cold-end d warm-end temperature differences. 

It was thought that the long equilibrium time for carbon resistors might be iue to the insulating cover surrounding the molded resistance element. Prelim-nary experiments on uninsulated carbon resistors (Allen Bradley type, 1/10 w, lominal room resistance 10 ohms) did not appear promising. 

Carbon Resistors, Pressure Transducers and Vibration Pickups Used for Measurements of Temperature, Pressure and Vibration at Liquid Hydrogen Temperatures (1) 114... 

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