Digital voltmeters are available commercially as digital panel meters for the measurement of both alternating voltage and steady voltage ( DC voltage). These are basically 200 mV, DVM modules, using either LED or LCD display. Large scale integrated circuit for the digital voltmeter of the Intel Corporation is 7107 that drives LED display. The same company offers 7106 I.C. for LCD display. With very few external components we can make the 200 mV module.
The digital multimeters are available with 3 ½, 4 ½ and 6 ½ digital display. They have over load protection, indication. They are provided with polarity indication, auto range change, and auto polarity change. The specifications of 4 ½ digital multimeter are given below.
Mode of Measurement | Accuracy (Better than) | Resolution |
d,c. : 200 mV-1000 V | ± 0.05 % rdg ± 2 dgt | 10 μ V |
a.c. : 200 mV-600 V, R.M.S. | ± 0.5 % rdg ± 0.3 F.S. | 10 nA |
Current. d.c. : 200 mA to 2 A | ± 0.4 % rdg ± 0.1 F.S | 10 nA |
Current a.c. : 200 mA to 2A | ± 0.6 % rdg | 10 nA |
Resistance : 200 W to 20 mW | ± 0.5 % rdg ± 0.3 F.S. | 10 mA |
Power supply : 230 V 50 Hz | ± 10 % for voltage | - |
Battery Operation Using 9 V battery | - | - |
The meter should be provided with over range indication. Non blinking switch. It is to be provided with auto display of polarity and decimal point.
The frequency range must be better than 10 kHz. Its input impedance must be 1 G Q. It is to be provided with BCD output.
Digital multimeters are commercially available with three and half digit display also. They have 26 functions and more depending on the cost and design. Frequency ranges better than 50 MHz are offered. Component test facility and facility to test transistors also is provided in some digital multimeters, besides the decimal read out. They are operated from 9 V compact battery. A provision for A.C. adaptor (eliminator) is made in all the digital multimeters.
The current trend in world class instrumentation is that a Cathode Ray Oscilloscope will also have a provision of a Digital Multimeter, making the instrument a two-in-one instrument.
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Multimeters