Electrical Indicating and Test Instruments 1 Introduction 161


Voltage-to-Time Conversion Digital Voltmeter



Yüklə 0,74 Mb.
səhifə3/14
tarix12.10.2023
ölçüsü0,74 Mb.
#154605
1   2   3   4   5   6   7   8   9   ...   14
1- MAQALA




Voltage-to-Time Conversion Digital Voltmeter


This is the simplest form of DVM and is a ramp type of instrument. When an unknown voltage signal is applied to input terminals of the instrument, a negative slope ramp waveform is generated internally and compared with the input signal. When the two are equal, a pulse is generated that opens a gate, and at a later point in time a second pulse closes the gate when the negative ramp voltage reaches zero. The length of time between the gate opening and closing is monitored by an electronic counter, which produces a digital display according to the level of the input voltage signal. Its main drawbacks are nonlinearities in the shape of the ramp waveform used and lack of noise rejection; these problems lead to a typical inaccuracy of 0.05%. It is relatively inexpensive, however.





Potentiometric Digital Voltmeter


This uses a servo principle, in which the error between the unknown input voltage level and a reference voltage is applied to a servo-driven potentiometer that adjusts the reference voltage until it balances the unknown voltage. The output reading is produced by a mechanical drum-type digital display driven by the potentiometer. This is also a relatively inexpensive form of DVM that gives excellent performance for its price.




Dual-Slope Integration Digital Voltmeter


This is another relatively simple form of DVM that has better noise-rejection capabilities than many other types and gives correspondingly better measurement accuracy (inaccuracy as low as 0.005%). Unfortunately, it is quite expensive. The unknown voltage is applied to an integrator for a fixed time, T1, following which a reference voltage of opposite sign is applied to the integrator, which discharges down to a zero output in an interval, T2, measured by a counter. The output–time relationship for the integrator is shown in Figure 7.1, from which the unknown voltage, Vi, can be calculated geometrically from the triangle as


(7.1)



Yüklə 0,74 Mb.

Dostları ilə paylaş:
1   2   3   4   5   6   7   8   9   ...   14




Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azkurs.org 2024
rəhbərliyinə müraciət

gir | qeydiyyatdan keç
    Ana səhifə


yükləyin