Many times we come across terms, ‘abc’ Multimeter is 3 ½, 4 ½, 6 ½, 7 ½ digits or 2000, 4000, 6000 counts. (‘abc’ means the manufacturer of multimeter)
We also come across the accuracy of ‘abc’ Multimeter is ‘0.15% + 2 digit’.
While buying Multimeter Digits and Counts is an important factor
What do these counts and digits mean?
Digits and counts are two different ways to express the same thing.
Take an e.g. of 3 ½ digit Multimeter.
The format is given as a whole number followed by a fraction, usually a 1/2 or a 3/4.
The whole number represents how many digits displayed from 0 to 9.
The fraction is ½ or a ¾.
Fraction ½ means the most significant digit for each range can be 0 or 1.
A ¾ means the most significant digit for each range is greater than 1.
3 ½ digit Multimeter can display three complete digits and one ½ digit. Three complete digits can have any numbers from 0 to 9 and one ½ digit can have only 0 or 1.
Three Positions of digits can display 0 to 9 numbers and leftmost position can only display 0 or 1 number in 3 ½ digit Multimeter.
Similarly for 4 ½,6 ½, 7 ½ digit Multimeter displays complete 0 to 9 numbers on four, six ,seven positions respectively and leftmost position displays only 0 or 1 number.
An illustration for 3 ½ Digit Multimeter Display (shown below)
A 6 ½ Digit Multimeter Display (as shown below)
A 7 ½ Digit Multimeter Display (as shown below)
An 8 ½ Digit Multimeter Display (as shown below)
If the display of Multimeter is 2000 counts. It can display digits from 0000 to 1999 counts. i.e. 3 ½ digit Multimeter.
If the display of Multimeter is 20000 counts. It can display digits from 00000 to 19999 counts. i.e. 4 ½ digit Multimeter.
Therefore, Digits and counts are two different ways to express same thing.
Counts are ignoring any decimal points and polarity signs.
Many newer Multimeters don’t have a restriction of 0 or 1 at leftmost digits.
Display of Multimeter is 4000 counts. It can display digits from 0000 to 3999 counts. I.e. leftmost digit can have 0,1,2,3 digits.
So, it is more practical to describe a Multimeter by its counts rather than digits.
Counts tell you what the instrument can display before it changes to the next range.
For example, suppose a Multimeter is of 20000 counts (4 ½ digit Multimeter). This means the range changes when it hits 20000 on display.
A 20000 count meter can read 19.999 V on the display, but when it tries to display 20 V, it will read 020.00 V instead or simply 20.00 V.
The Multimeter moves to the next range mean one digit of resolution is lost.
Generally 2000 Count Multimeter (3 ½ digit Multimeter) have range 200.0 mV, 2.000 V, 20.00 V, 200.0 V.
Generally 6000 Count Multimeter have range 600.0 mV, 6.000 V, 60.00 V, 600.0 V
The count refers to the limit of the highest value the Multimeter will display for each range.
As soon as a measured value reaches this limit, the range will move up and the resolution will be downgraded by a factor of 10, that is, the decimal place will be moved to the right one spot.
If we had a Multimeter that was designed to measure up to 1000V with a 40000 count, then, the ranges and resolution can be as follows:
0.0000 to 3.9999 with a resolution of 0.0001
4.000 to 39.999 with a resolution of 0.001
40.00 to 399.99 with a resolution of 0.01
400.0 to 1000.0 with a resolution of 0.1
The accuracy of Multimeter is written as “0.15% + 2 digits”
Means 0.15 % of indicated value + 2 × Resolution
Reading of Multimeter at 1 volt is 1.005 V
Resolution is 0.001 V
Accuracy = (0.15% × 1.005) + (2× 0.001)
Accuracy = 0.0035 V
Author: Saurabh Vaidya
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