Jack's corner

  Analog and Digital Meters are two types of instruments Amateur Radio Operators
use to troubleshoot and perform electrical measurements. The Analog Meter is
often called a VOM “VOM” is an acronym, derived from the first letters of the
electrical measurements (volts, ohms, milliamperes), which the meter performs.
Such Meters may equally often be referred to as Voltmeter, Ammeter, Ohmmeter,
Multimeter or Multitester. VOM’s have a needle that deflects along a graduated
or incremental scale pointing to the measurement of the specified quantity.
Measurement accuracy’s of 3 - 4% are typical. VOM’s often have a low internal
resistance (input impedance). Which is not a desirable characteristic for a
Meter? Low impedance loads the circuit under measurement and contributes to
measurement errors. The Analog Meter has an inherently low effective resolution
since the user must estimate (interpolate) values between the fixed graduations.
 

    Although the Analog Meter is less accurate then the Digital Meter, its advantage
is a faster response time. Digital Meters also measure, voltage, current and
resistance. The measured value is read directly on a digital display. Digital
Meters are often called DVM’s (Digital Voltmeters) or (Digital Multimeters).
Digital Meters convert all measurements to voltage prior to digitization,
regardless of the measurement function chosen; this is why Digital Meters are
often called DVM’S. VOM’s on the other hand, convert all measurements to
current, which is why they're specified in terms of “ohms per volt”. Digital
Meters have a significant advantage compared with their analog counterparts.
High internal meter resistance (producing negligible circuit loading), together
with the measurement accuracy’s in the order of .05% -1.5% makes the DVM an
attractive measurement instrument for the Radio Amateur. Combining this with
good resolution (resolution refers to how small or fine a measurement the meter
can make), the digital display excels, displaying three or more digits for each
measurement. VOM’s have a maximum measurement burden. If the VOM is loaded with
a measurement beyond this value, the meter will not recover and becomes
defective. Digital Multitesters contain protective overvoltage circuits that
prevent accidental damage by allowing the instrument to recover without
permanent damage. A fuse in series with the input lead usually protects the
Digital Meter. VOM’s have a faster response time (the time it takes for the
needle pointer to move to the correct measurement) then Digital Meters. This is
because it is easier for the eye to track the pointer then to interpret the slow
update of the digital display. Digital Meters have “response times” (display
update times) of 1 to 2 seconds. The speed of a VOM is one advantage the Analog
Meter has over a Digital Meter. Auto ranging, auto polarity, hold functions,
continuity buzz and diode junction measurements are virtues of some Digital
Meters.

 Additional information about Analog and Digital Meters: ARRL Amateur Radio
Handbook
 

Add comment


Security code
Refresh

1000 characters left