摘要:

After annealed, type K (Chromel vs Alumel) thermocouples were heated above 200 °C, their temperature measurements were in error up to 1.3%, as determined by comparison calibrations to working standard 90% Pt–10% Rh/Pt thermocouples or platinum resistance thermometers. Reannealing the type K thermocouples removed the errors. The errors were due to changes in the thermal emf vs temperature relationship of the type K thermocouples, which from previous work of others can be attributed to short‐ranged ordering of the Chromel thermoelements. Reannealing the thermocouples removed the errors because the order–disorder transformation is reversible; that is, short‐ranged ordering of the Ni and Cr atoms of the Chromel alloy occurs between 200° and 600 °C, and disordering occurs above 600 °C. The traveling gradient method was used to determine the effects of heat treatment on the thermal emf of type K thermocouples, to investigate the kinetics of ordering of Chromel, and to determine the amount of order produced by heat treatments. Though the order–disorder transformation could not be stopped, our results demonstrate that there exists an optimum amount of order in the Chromel thermoelement to yield a repeatable thermal emf vs temperature relationship for a type K thermocouple in a specific application. When the experimental conditions of the application were controlled carefully, isothermal heat treatment to produce the optimum order in the Chromel thermoelements and calibration of the type K thermocouples prior to use essentially eliminated the temperature measurement errors due to order. The optimum amount of order depended on the application and was determined experimentally. Variations from the optimized heating or cooling cycles, changes in the depth of thermocouple immersion during use, or modification of the temperature gradient on the thermocouple caused temperature measurement errors of up to 1% with ordered and calibrated type K thermocouples.

ISSN:0034-6748    

DOI:10.1063/1.1134086

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A simple ac bridge for the measurement of the capacitance of lipid bilayer membranes between 100 Hz and 10 kHz with a nominal accuracy of about 0.1% without corrections is described. The voltage across the unknown need be only 7 mV (rms). Using a simple calibration procedure, the capacitance can be determined with a nominal accuracy of 0.05%. The resolution of the bridge is about 1 part in 20 000. The novel features of the bridge are (1) 100:1 resistance ratio arms and a floating unknown, (2) a single‐ended output and a balanced input utilizing a photocoupled isolator, and (3) a detector to monitor voltage across the unknown at balance.

ISSN:0034-6748    

DOI:10.1063/1.1134087

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A capacitance dilatometer is described which automatically records the height of a mercury column as a function of time. Changes as small as 10−4ml have been detected, with an instrumental stability allowing experiments of several days’ duration. The technique is based on the measurement of the capacitance of an aluminum foil‐covered, precision bore, glass column containing Hg. The dilatometer has been used to measure coefficients of expansion and rates of polymerization and hydrolysis.

ISSN:0034-6748    

DOI:10.1063/1.1134088

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Instrumentation for rapidly acquiring, storing, and processing laser Doppler velocimeter data is described. Electrical pulses having amplitudes that are inversely proportional to the Doppler frequencies are generated and then counted with a multichannel analyzer. Velocity distribution data may then be printed out, graphically displayed, or computer processed.

ISSN:0034-6748    

DOI:10.1063/1.1134089

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The use of tunnel junctions as pressure monitoring devices in both solid and fluid pressure transmitting media is described. While very sensitive to pressure changes, these devices have been found to have a negligible dependence on temperature over the range 0–77 K. Their pressure response has been found to be reversible and if maintained at temperatures less than 77 K, they can be used for prolonged periods. An actual example of their use at low temperature is given.

ISSN:0034-6748    

DOI:10.1063/1.1134090

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A complete analysis of pulsed NMR signals requires the knowledge of the time dependence of the components of the signal in phase and out of phase with the pulse. In practice, the NMR signal is processed by a pair of (approximately) orthogonal phase‐sensitive detectors, the filtered outputs of which can be sampled, digitized, and stored repetitively. The present paper describes a software technique for correcting these stored signals for the lack of orthogonality of the two phase‐sensitive detectors, the difference between their sensitivities, the overall phase shift in the spectrometer, and the difference between the reference frequency of the spectrometer and the frequency of the center of a reference NMR line. The necessary information is derived (also by software) from measurements performed on a single symmetric NMR absorption line.

ISSN:0034-6748    

DOI:10.1063/1.1134091

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A vibroscope is an instrument designed to measure the mass per unit length or changes in the mass per unit length of a fiber. While a variety of mechanical transducers have been used in the past, all automatic vibroscopes have used conventional oscillator feedback, and this has often proved unsatisfactory. A new form of feedback involving phase detection has been applied to yield a very reliable system.

ISSN:0034-6748    

DOI:10.1063/1.1134082

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

An apparatus for inelastic neutron scattering experiments at low temperature is described. This pressure assembly consists of an autofrettaged aluminum 7075‐T6 alloy cell and a shield. The rupturing pressures for some cells have been measured at different temperatures; the efficiency of the shield has also been tested. These studies demonstrate the feasibility and the safety of experiments under high pressure up to 4 kilobar even at very low temperature.

ISSN:0034-6748    

DOI:10.1063/1.1134083

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A low noise ion detector for microimpurity analysis with a quadrupole mass spectrometer has been developed using the off‐axis technique with an electrostatic deflector plate and a channel electron multiplier. This arrangement of ion detector can greatly reduce the noise and baseline shifts caused by photons and excited neutrals, which are dependent on the emission current and pressure in the ion source. The ion collection efficiency of 100% in this arrangement is obtained at a multiplier voltage of −3 kV and a deflector voltage of 10 V. The noise count rate was on the order of 1–2 Hz. The off‐axis ion collector gives a factor of 140 increase in effective sensitivity of the mass spectrometer. The minimum detection limit of the mass spectrometer with the off‐axis detector is also determined.

ISSN:0034-6748    

DOI:10.1063/1.1134084

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Three designs of ac bridge circuits for use in carbon or germanium resistance thermometry at low temperature are presented. These circuits combine simplicity of design with high sensitivity and stability of calibration during a low‐temperature run and enable the performance of the bridge to be checked accurately. The designs are intended for use in applications in which the thermometer can be calibrated during each low‐temperature run. The combination of these designs as alternate modes of operation of a single, versatile, practical bridge circuit is described. The operation of this bridge with regard to sensitivity and noise is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1134085

出版商:AIP    

年代:1975

数据来源: AIP