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The time constant
A constant representing the transition time course of the reaction. Means that the physical decay time from the maximum to 1 / e of the maximum value required. For a certain amount of decay exponentially, the amplitude decay is 1 / e times the time constant is referred to as the time required. [1] In the various fields of application, the time constant also have different specific meanings.
The time constant circuit
A constant representing the transition time course of the reaction. In the resistance , the capacitance of the circuit, which is the product of resistance and capacitance. If the unit is mF C (microfarads), R units are milliohms (megohms), the time constant
The unit is second. In such a circuit when the constant current I flows, the voltage across the capacitor reaches the maximum value (equal to IR) of 1-1 / e i.e. approximately 0.63 times the time that is required for the time constant
, And when the circuit is broken, the time constant of a capacitor terminal voltage reaches the maximum value 1 / e, i.e., about 0.37 times the time required. [2]
RLC circuit transient time constant in an RC circuit , the capacitor voltage Uc is always the initial value UC (0) monotonically decay exponentially to zero, the time constant
=RC。
NOTE: When seeking time constant, than the capacitance of the circuit considered active two-terminal network , the power is set to zero, and then determine the equivalent resistance of the active two-terminal network is the R in the RL circuit, always the initial iL value iL (0) monotonically decay exponentially to zero, the time constant
=L/R
Mechanical time constant of the motor
Motor mechanical time constant is the time required for this given motor rated voltage, no load, speed up to 63% of rated speed. [3]
This parameter is a measure of the main characteristics of the motor is started, such as the coreless motor, usually about 1-50ms. The time constant of the Greek alphabet
(Tao four tones) to represent.
The time constant of heat transfer
It refers to the time constant of the thermocouple when analyzed using lumped parameter method, the object over time than the temperature dropped to 36.8% over the initial temperature required for the remainder. [4]
In the case of measuring the fluid temperature by a thermocouple in the thermocouple is a time constant of the variation of the response speed of the fluid temperature indicator.
The time constant of the radioactive logging tool
Radioactive logging instrument time constant determined by the count rate meter integrated circuit product of the resistance and capacitance whose value is selected according to the count rate measurement accuracy, and logging speed requirements. Count rate, it would take large time constant in order to ensure the necessary precision; but large time constant, large instruments inert, i.e., a corresponding decrease in logging speed. [1]
Time constant electrocardiograph
One technical indicators electrocardiograph, * refers to the standard square wave decreases from the maximum sensitivity (100%) time to 37% of the amplitude of the magnitude required, in seconds. Time constant related to the rate of decline in the electrocardiogram wave, the longer the amplitude decreased more slowly, and vice versa faster. Checking, with a walking speed of 25mm / s of the paper, to 1mV standard voltage, so that a pen move upward and hold 1mV 10mm ammonium button does not move, and then let go and stop the paper until a pen down from the maximum amplitude to the baseline. Analysis, the small number of cells dropped by the square wave 3.7mm to 10mm required by the 0.04s, namely the time constant of the electrocardiograph. Time constant electrocardiograph general ≥3.2s. [5]
