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Electrical measuring instruments and measurements
Published in John Bird, Electrical and Electronic Principles and Technology, 2017
An ohmmeter is an instrument for measuring electrical resistance. A simple ohmmeter circuit is shown in Fig. 12.5(a). Unlike the ammeter or voltmeter, the ohmmeter circuit does not receive the energy necessary for its operation from the circuit under test. In the ohmmeter this energy is supplied by a self-contained source of voltage, such as a battery. Initially, terminals XX are short-circuited and R adjusted to give f.s.d. on the milliammeter. If current I is at a maximum value and voltage E is constant, then resistance R = E/I is at a minimum value. Thus f.s.d. on the milliammeter is made zero on the resistance scale. When terminals XX are open circuited no current flows and R (=E/O) is infinity, ∞
Compressive quasi-static and dynamic piezoresistive behavior of carbon black and carbon nanotubes elastomer composites: Experimental study
Published in Bertrand Huneau, Jean-Benoit Le Cam, Yann Marco, Erwan Verron, Constitutive Models for Rubber XI, 2019
N. Penvern*, A. Langlet, M. Gratton, N. Aït Hocine
The resistance of the samples is measured using a dynamic ohmmeter. The measurable resistance of the ohmmeter is in the range 0 – 450 kΩ. The strain of the sample is evaluated through the displacement of the upper head, using Equation 1: ε=uL0 where u = displacement; and L0 = initial length of the sample.
Diode
Published in Muhammad H. Rashid, Ahmad Hemami, Electricity and Electronics for Renewable Energy Technology, 2017
The simplest way to test if a diode functions or it is damaged is to measure its resistance with an ohmmeter. A diode should exhibit little resistance to the electric current in one direction (when the diode is connected to the ohmmeter terminals) and a large resistance when the connections are switched. If the diode conducts in both directions or if it shows an infinite (or very large) resistance in either way it is connected, then it is damaged. In the former case, the diode is shorted, and in the latter case it is open.
Design of blasting patterns to induce effective caving in continuous miner depillaring panel – a case study
Published in Mining Technology, 2021
Pijush Pal Roy, Chhangte Sawmliana, Rakesh Kumar Singh
Induced caving by blasting is always a very sensitive operation that needs to be monitored carefully to assess the efficacy of the design patterns. The following generalized guidelines are suggested for this purpose: Sufficient support should be provided near the blasting site during drilling as well as charging of holes in order to prevent any roof fall. Before blasting, the support may be withdrawn from the site depending on the prevailing ground conditions.It is essential to check the presence of methane before charging of blast holes at the site in order to prevent any chance of gas explosion.Before charging holes with explosives, the actual depth of holes should be checked and measured. If any blast hole gets choked or jammed due to the presence of cracks or strata pressure, the quantity of explosive charge should be adjusted accordingly.The electric detonators should be checked before charging of blast holes with an approved Multimeter or Ohmmeter to prevent any chance of misfire.More than 4 m distance should be left between the barrier pillars and the nearest blast hole in order to prevent damages of barrier pillars at the time of induced caving by blasting.Proper stemming of blast holes should be done. Uncharged portion of holes should be packed completely with the stemming materials.Proper care should be taken while withdrawing the supports to prevent any damage to the firing connection made for blasting.To prevent any chance of misfire, the exploder should be charged properly and checked for the capacity of the number of shots that can be fired by it.Before firing the blasting round, all manpower must be shifted to a safer place, proper shelter must be taken.While blasting from the surface, the deviation of drill holes must be taken care of. If the depth of the cover exceeds 100 m, it is always better to drill holes of diameter 154 mm (6 inch) or more. Burden and spacing may be changed depending upon the situation. The selection of site should be precisely done with the help of an experienced surveyor.