What do Digits & Counts mean in Multimeter?

Sudha MApril 12, 2023

647 6 minutes read

What is Multimeter?

A multimeter is a digital device that measures voltage, amps, and resistance across circuits by joining two contacts to various parts of an electrical system.
A multimeter is more than one thing. A multi-range DC voltmeter, multi-range AC voltmeter, multi-range ammeter, and multi-range ohmmeter are all combined in one instrument. It is completely filled with all the components required for this arrangement.
Multi-meters can be used by technicians to identify levels of voltage and resistance, as well as changes in electrical currents.
Since these Digital multimeter used for measurement comes in various makes and models.
A multimeter is 3 & ½, 4 & ½, 6 & ½, 7& ½ digits or 2k, 4k, or 6k counts.
Generally, the accuracy of the Multimeter is ‘0.15% + 2 digits
But, the two main factors Multimeter Digits and Counts make more noise in selecting a multimeter for our application.

Counts and digits are two distinct methods of expressing the same thing.
Counts and digits are synonyms for describing the resolution of a digital multimeter.
Today, total counts are more commonly used to categorize digital multi meters than digits.
The resolution of a digital multimeter is also specified in counts.

Consider 3 ½ digit Multimeter.
This format is expressed as a whole number followed by a fraction of ½ or a ¾.
The whole number defines actual digits displayed from 0 to 9.
The fraction is ½ or ¾.
Fraction ½ defines MSD for each range maybe 0 or 1.
A ¾ means the MSD for each range is greater than 1.
A 3 ½ Digital Multimeter displays three full digits and one-half digits.
Three full digits include any numbers from 0 to 9, and one ½ digit can have only 0 or 1.
In the 3 ½ Digital Multimeter, the three-digit position displays 0 to 9 numbers, and the leftmost position can only display 0 or 1.
Similarly for other types of Digital Multimeter like 4 ½, 6 ½, 7 ½, & 8 ½, the Four, Six, Seven, & Eight positions display complete 0 to 9 numbers, & the leftmost position or ½ position displays only 0 or 1 number.
The schematic of various DMM is shown below.

Here, this 3 ½ Digital multi-meter display has 2000 counts, It indicates a digital value from 0000 to 1999 counts.

Here, this 4 ½ Digital multi-meter display has 20000 counts. It indicates a digital value from 00000 to 19999 counts.
Therefore, advanced Multi-meters do not have a restriction of 0 or 1 at the left most digits

Example: Practically it is easy to define or specify a Multimeter by its counts rather than digits.

If the Multimeter display has 4000 counts. It indicates a digital value from 0000 to 3999 counts.
A count informs us what the instrument will display before it changes to the next range.
A multimeter can read 19.999 V instead of 20.0V having a count value of 20000.
But, this multimeter displays 020.00 V instead or simply 20.00 V.
The range and resolution values for DMM are intended to measure 1000V with a count of 40k

The accuracy of DMM is characterized as the highest acceptable error occurring under particular circumstances of operation.
It’s represented by a percentage and informs us how comparable the displayed measurement is to the exact (standard) value of the measured signal.
Accuracy necessitates a comparison to an industry standard.
Depending on the application, the accuracy of a digital multimeter is essential.
Most AC power cable voltages may vary around 5% or more.
A voltage measurement considered at a standard 115 V AC receptacle is an example of this model.
A digital multimeter with measurement accuracy of 3% is appropriate if a digital multimeter is only used to check if a receptacle is energized.
Higher accuracy may be required for some applications, such as the calibration of automotive, medical aerospace, or specific industrial equipment.
A digital multimeter reading of 100.0 V with a 2% accuracy can vary from 98.0 V to 102.0 V.
This holds good only for some applications, but these are not good for sensitive electronic equipment.
Accuracy can also involve the inclusion of a specified amount of digits (counts) in the basic accuracy rating.
For example, a (2%+2) accuracy means that a reading of 100.0 V on a multimeter can range between 97.8 V and 102.2 V.
The use of a higher-accuracy digital multimeter opens up a wide range of possibilities.
Fluke handheld digital multimeter have basic dc accuracy ranging from 0.5% to 0.025%.

Precision is an ability of a digital multimeter to deliver an identical measurement again and again.
The arrangement of holes on a shooting range target is a typical method used to describe precision.
This example defines that a rifle is directed towards the target’s bulls-eye and fired from the same position every time.
If the holes are close together yet separate from the bulls-eye, the rifle is said to be precise but not accurate.
The rifle is said to be more accurate and precise if the holes are tightly packed within the bulls-eye.
It is neither accurate nor precise if the holes are distributed randomly across the target).
Precision, or repeatability, is much more significant than accuracy in some situations.
When measurements can be replicated, an error pattern could be recognized and rectified.

Resolution is the minimum increment that can detect and display.
Consider two rulers as an example of a nonelectrical case.
One with 1/16-inch hatch marks has better resolution compared to the one with quarter-inch hatch marks.
Consider testing simple 1.5 V household batteries.
If the resolution of DMM is 1 mV in the 3 V range, it is easy to see a change of 1 mV at the time of voltage reading.
The user visualizes small changes like 0.001 at the 3 V range.
Reducing the digital multimeter range setting improves resolution as long as the measurement is within the set range.

Digital multimeter range and resolution are linked to each other and specified in their specifications.
The majority of DMM available in the market come with an auto-range function to select the appropriate range that depends on the magnitude of the measurement.
This provides the most accurate measurement resolution as well as meaningful reading.
The multimeter will display OL if the measurement exceeds the specified range (overload).
Without burdening the multimeter, the most accurate measurement is obtained at the lowest possible range setting.

Counts and digits are terms used to describe the resolution of a digital multimeter.
Digital multimeters are classified based on total counts rather than digits.

The Fluke product line includes digital multimeter with 3 ½ and 4 ½ digits.
A 3 ½ digit digital multimeter displays three full digits and half digits for a number ranging from 0 to 9.
The half digit is regarded as the MSB.