Resistors voltage sensitive

It is evident that the double layers at the grain boundaries constitute Schottky barriers which are similar in some respects to those formed in VDR resistors. In accord with this it is found that the resistivity-temperature relation of PTC material is voltage sensitive. The low-temperature resistivity may be reduced by a factor of 4 by an increase in applied field from 1 to 80kVm-1, and the ratio of maximum to minimum resistivities, above and below Tc, may be reduced from five to three orders of magnitude. 

The output from a voltage sensitive or resistor feedback preamplifier is a tail pulse with a rather long decay time. Hence, some pulse pile-up is unavoidable, except at very low count rates. Pile-up will cause the average level of this signal to increase with pulse rate, which may approach the limit of linear operation of the preamplifier. 

The main categories of electrical/optical ceramics are as follows phosphors for TV, radar and oscilloscope screens voltage-dependent and thermally sensitive resistors dielectrics, including ferroelectrics piezoelectric materials, again including ferroelectrics pyroelectric ceramics electro-optic ceramics and magnetic ceramics. 

Modern techniques use thin-film resistors deposited directly on the area and semiconductor units are available which are considerably more sensitive than the resistive type. Dynamic measurements can also be made. The change in resistance unbalances the bridge, causing a voltage to appear across the detector terminals. This voltage is then amplified and applied to a CRO or the information can be stored digitally for future retrieval. 

One temperature-sensitive resistor as compensator and another one as detector are integrated into adjoining strings of a Wheatstone bridge circuit the voltage can be measured. Since both resistors are exposed to the test gas flow, disturbances caused by changes in temperature and humidity are compensated. 

The reaction is initiated by the addition of a reactant, which must be exactly at the same temperature as the Dewar contents, in order to avoid the sensitive heat effects. Then the temperature is recorded as a function of time. The obtained curve must be corrected for the heat capacity of the Dewar flask and its inserts, respective of their wetted parts, which are also heated by the heat of reaction to be measured. The temperature increase results from the heat of reaction (to be measured), the heat input by the stirrer and the heat losses. These terms are determined by calibration, which may be a chemical calibration using a known reaction or an electrical calibration using a resistor heated by a known current under a known voltage (Figure 4.2). The Dewar flask is often placed into thermostated surroundings as a liquid bath or an oven. In certain laboratories, the temperature of the surroundings is varied in order to track the contents temperature and to avoid heat loss. This requires an effective temperature control system. 

In addition to the sensitivity of the detector, the other concern is how fast it responds to a change in the intensity of light. Equation 6.53 gives the voltage drop Vt t) on the load resistor R that will be fed to the SH and digitizer (Figure 6.10). 

Figure 8 shows a basic bridge circuit which consists of three known resistances, Rx, R2, and R3 (variable), an unknown variable resistor Rx (RTD), a source of voltage, and a sensitive ammeter. 

The RF SQUID is based on the AC Josephson effect, uses only one Josephson junction, and is less sensitive than the DC SQUID, but is cheaper and easier to manufacture its SQUID is inductively coupled to a resonant tank circuit. Depending on the external magnetic field, as the SQUID operates in the resistive mode, the effective inductance of the tank circuit changes, thus changing the resonant frequency of the tank circuit. These frequency measurements can be easily done, and thus the losses that appear as the voltage across the load resistor in the circuit are a periodic function of the applied magnetic flux with a period of 0. 

The accuracy of a voltage measurement depends most of all on the design and the quality of the potentiometer unit used. For a precision potentiometer, the relative accuracy of measurement (ability to measure very small changes in voltage) wUl depend a great deal on the null detector sensitivity, while the absolute accuracy will depend more on the accuracy of the standard-cell voltage value and the linearity of the slide-wire. The most accurate potentiometers replace the slide-wire by discrete resistors and switches. 

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