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More than Circuit EngineeringPulse-width Modulator In Accurate Measurements
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Pic.1. Pulse-width
Modulator on Double Univibrator Ê155ÀÃ3.
- Variable-capacitance
Transducer. 
- Stray Capacitance in the Line. Q1 & Q2 - Pulse width.
is determined by a formula: 
.
Lets 
.
Applying Circuit of
compensations in Outputs of Univibrator we have: 
(Pic.2.)
Pic.1. Pulse-width
Modulator on Double Univibrator Ê155ÀÃ3 Circuit.
Pic.2. Pulse-width
Modulator Diagram.
Output Signal is determined by a formula: 
,
U = U(t) – Value of measuring parameter. 
- Interference with Period
,
where 
(f
–
Frequency of Interference with a period 
),
– Maximal value of
Interference. Then for a period Ò is necessary to conduct n averaging for reduction
to 
of Random Error. Systematic Error from
Electric Interference reduces to zero. Conducting integration for a period Ò, we can write
down:
We conduct a Discrete
Accumulation of Signal after Pulse-width Modulator and Voltage-to-Frequency
Converter. Time of one measuring 
,
Input Signal is described
by a formula:
i = 1, 2…n.
Using formulas (1),
(2), (3) & (4) we can write down:
If 
,
then 
,
& 
(Pic.3.)
,
V/s
(Pic.4.)
- Relative Pulse Duration.
Pic.3
Pic.4
Minimum dependence on a Temperature is provided by a selection of necessary Resistors and Condensers R1, R2, C1, C2. (Resistances Temperature Factor and Capacitor Temperature Factor for R1, R2, C1, C2).
added 18.07.07 00:59:29 | 
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