scholarly journals On the construction of a standard high-frequency inductive resistance and its measurement by a thermal method

1925 ◽  
Vol 109 (751) ◽  
pp. 508-522
Keyword(s):  
Radio Frequency ◽  
Direct Current ◽  
High Frequency ◽  
Wheatstone Bridge ◽  
Effective Resistance ◽  
Thermal Method ◽  
Thermal Methods ◽  
Direct Current Resistance ◽  
Complete Circuit ◽  
Parasitic Currents

The ordinary methods of measuring the radio-frequency resistance of inductance coils depend on the measurement of the resistance of a complete circuit, containing, usually, the coil, a thermo-ammeter, a condenser and leads. The lack of knowledge of the effective resistance of the circuit outside the coil, of the losses induced in the surrounding objects, and of the distribution of parasitic currents, leave some doubt on the reliability of the value of the resistance obtained by these methods. To obtain reliable measurements it is necessary to fall back on some thermal method by means of which the power lost in the coil itself can be measured quite independently of the circuit and neighbouring bodies. The method described in this paper was carried out essentially as a check to the usual methods of measurement. A number of investigators have used thermal methods to measure the effective resistance of coils. Amongst them may be mentioned T. P. Black, L. W. Austin, H. Abrahams, Gr. W. O. Howe, and L. Lehrs. T. P. Black (1) compared the effective resistance of long solenoids with the effective resistance of straight wires, employing a method resembling that of J. A. Fleming (2) for measuring the high-frequency resistance of straight wires by means of a differential air thermometer. L. W. Austin (3) compared the heat given out by a coil when current at radio frequencies and direct current were passed through two similar coils. The coils were immersed in oil, and the equality of temperature noted by thermo-junctions connected in opposition in the two vessels. H. Abrahams (4) compared the rise of temperature of coils after passing radio-frequency current and then direct current by quickly finding the change in the direct-current resistance measured by a Wheatstone bridge. G. W. O. Howe (5) found the rise of temperature of long solenoids by means of a thermojunction placed near the centre, and compared the effect of direct and highfrequency currents. He thus assumed that the loss is uniformly distributed along the coil, an assumption which will hold only if the coil is long. L. Lehrs (6) enclosed the coil in a vessel connected to a very sensitive manometer, and adjusted the alternating and direct currents so that no change could be observed on switching from one to the other.

scholarly journals A method of measuring the effective resistance of a condenser at radio frequencies, and of measuring the resistance of long straight wires

1932 ◽  
Vol 137 (831) ◽  
pp. 116-133 ◽  
Keyword(s):  
Energy Loss ◽  
Resonance Method ◽  
Effective Resistance ◽  
Circular Disc ◽  
Solid Dielectric ◽  
Thermal Method ◽  
Thermal Methods ◽  
Elegant Method ◽  
Air Condenser ◽  
Total Capacity

When the effective resistance of a high frequency circuit is measured by a resonance method, it is usual to find that the resistance exceeds the calculated resistance of the coil. Some of the discrepancy may be due to energy loss in the condenser, and it is desirable to have some means of measuring this loss. The energy loss in high power condensers is now measured regularly by thermal methods and may be as small as 0·025 per cent. of the volt ampere product. But a thermal method is impracticable for the small condensers used in a laboratory because the power absorbed would be less than 0·1 W. Most of the energy loss in an air condenser is presumably due to the dielectric supporting the plates and to poor contacts between the plates. Dye has developed ma very elegant method for measuring the energy loss in a condenser, which presumes that all the loss occurs in the solid dielectric. In his method there is a special condenser which consists of two capacities in parallel, and screened from one another. One portion of this compound condenser contains the insulating supports for the second portion. Accordingly the second portion contains no solid dielectric and is a pure air condenser and is presumed to have no loss. This condenser consists of a single circular disc, which may have one of three sizes, contained within a cylindrical box; the plate hangs from a metal stem which is supported on quartz blocks contained in a chamber above the cylindrical box. The total capacity may be considered to be in two parts. One between the metal stem and the case and having a dielectric which is partly quartz and therefore imperfect; the other between the circular disc and the case and having no dielectric except air and therefore being perfect. The condenser to be tested can be connected in parallel with the special condenser and its capacity is adjusted to be equal to that between the circular disc and the case. The disc can be detached from the stem and so leave only the imperfect portion of the special condenser. The condenser under test is then placed in parallel with the imperfect portion, resulting in a total capacity unchanged by the substitution process. But the substitution has replaced a capacity without loss for an equal capacity with loss. The total circuit resistance is measured by a resonance method before and after the substitution and the difference of value is ascribed to the loss in the condenser under test. Since the special condenser is provided with three different discs the resistance of the condenser under test could be measured at three different settings.

scholarly journals THE DIRECT CURRENT RESISTANCE OF NITELLA

1930 ◽  
Vol 13 (4) ◽  
pp. 495-508 ◽  
Author(s):  
L. R. Blinks
Keyword(s):  
Direct Current ◽  
Tap Water ◽  
High Mobility ◽  
Wheatstone Bridge ◽  
Living Cells ◽  
Transient Effects ◽  
Intact Cells ◽  
Direct Current Resistance ◽  
Opening And Closing ◽  
String Galvanometer

The electrical resistance of Nitella cells to direct current is determined in a Wheatstone bridge, using a vacuum-tube detector, and string galvanometer. Very small currents are passed through the cells, to avoid stimulation. The galvanometer record shows typical transient effects in the living cells at opening and closing of the circuit, due to the development of back E.M.F. With 1 cm. contacts of tap water, and 1 cm. between contacts the resistances of living cells are usually between 1,000,000 and 2,000,000 ohms. They go as high as 3,500,000 ohms when the cells are in the best condition. The resistance falls to about 50,000 ohms immediately after killing. Leakage around the cell is small because the wall is imbibed with tap water. By measuring the resistance of the isolated wall (air-filled), and by varying the areas of contact with intact cells, the effective protoplasmic resistance is calculated. This varies from 100,000 to 700,000 ohms per square centimeter of surface, with a typical value of about 250,000 ohms per square centimeter. This high resistance represents a low permeability for most ions, since the values are nearly as high with contacts of 0.01 M NaCl, CaCl2, LiCl, NH4Cl, and MgSO4. The resistances are greatly reduced however by solutions of KCl, which is correlated with a high mobility of the K+ ion in the protoplasm. Electrical stimulation causes a marked reduction of resistance, which may be due to exomosis of KCl.

scholarly journals THE DIRECT CURRENT RESISTANCE OF VALONIA

1930 ◽  
Vol 13 (3) ◽  
pp. 361-378 ◽  
Author(s):  
L. R. Blinks
Keyword(s):  
Cell Wall ◽  
Direct Current ◽  
Living Cells ◽  
Effective Resistance ◽  
Vacuum Tube ◽  
Direct Current Resistance ◽  
Valonia Ventricosa ◽  
Current Resistance

A direct current bridge with vacuum tube detector is described for measuring the resistance of living cells. Methods for evaluating the surface of contact with the protoplasm, and the leakage around the cell wall, allow us to calculate the effective resistance of the protoplasm. In Valonia ventricosa this is usually at least 10,000 ohms per square centimeter and is often much higher. This is in agreement with the very slight ionic interchange observed in normal Valonia.

A New Automatic Demultiplexing Method for NRZ-OOK Polarization-Division Multiplexed System

2011 ◽  
Vol 204-210 ◽  
pp. 1636-1639
Author(s):  
Qi Jing ◽  
Yong Qing Huang ◽  
Yang An Zhang ◽  
Ming Lun Zhang ◽  
Li Dong Mei
Keyword(s):  
Radio Frequency ◽  
Direct Current ◽  
Beam Splitter ◽  
System Simulation ◽  
Polarization Controller ◽  
Polarization Beam Splitter ◽  
Optical Polarization ◽  
Control Signals ◽  
Detection Window

A new automatic optical polarization demultiplexing method for NRZ-OOK polarization division multiplexed (PDM) system is proposed. The detected power differences of both the direct current (DC) and the radio frequency (RF) are used as control signals which are sensitive to the angles between the polarization controller (PC) and the polarization beam splitter (PBS). The characteristics of those control signals are thoroughly analyzed, and the best RF detection window is calculated out through system simulation.

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