How to Calculate the Resolution of a Digital Multimeter

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Digital multimeters, once referred to as voltmeters, have been known as the tape measure for engineers and electricians in the new modern world. These devices are necessary for troubleshooting, testing, and designing with electrical circuits and electronics involved in nearly all industrial and consumer products. 

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Keep in mind that digital multimeters or DMMs are devices for measuring amperes (A), ohms (Ω), and volts (V). Many digital multimeters have other unique features and qualities. Nonetheless, measuring such three variables is considered to be the foundation for every electrical measurement.

It would help if you also understood the various ways digital multimeters show their measurements. One of them is through resolution.

What Does Resolution Mean in Digital Multimeters? 

Resolution relates to how fine the measurement of a digital multimeter is. Understanding and learning the multimeter’s resolution enables you to identify if it can notice a trivial change in the measured signal.

For instance, your digital multimeter has a resolution of 1 mV on the 4 V range. So that can notice a change of 1 mV or 1/1000 of a volt while reading a 1 V signal. 

You will not purchase a ruler labeled in one inch or 1 cm segments when you need to measure down one millimeter or a quarter inch. Further, a thermometer measuring only in whole degrees is not much use if your average temperature is 98.6 degrees Fahrenheit. You will require a thermometer along with a one-tenth-degree resolution.

Remember that resolution determines the smallest possible measurement change the equipment, device, or instrument can detect. Hence, a 1000 count digital multimeter can show a change of .001 unit at their lowest ranges, while 10,000 count instruments can locate .0001. 

In short, it is ten times the resolution of the 1000 count digital multimeter. Moreover, the resolution depends on the size of every unit (take note: the smaller, the better). Hence, the lowest possible range must be chosen when doing high-resolution readings. 

Nonetheless, such figures say nothing about the accuracy of the instrument or device. For example, the 1000 count digital multimeter might have a measurement uncertainty that is much smaller than the 10,000-count model. Therefore, it creates many accurate readings.

Resolution is an integral factor in measuring uncertainty, but it’s not the only factor. 

Now that we are on the topic of DMM’s measurements, here are other ways you can see them:

  • Accuracy

Accuracy is considered the biggest allowable error in your digital multimeter readings. It indicates how close the displayed measurement of your meter is to the real value of the signal being measured.

Keep in mind that accuracy is normally shown as a percent of the reading. For instance, one percent of the reading accuracy indicates that for a display of 100 volts. Hence, the real value of the voltage could be around 99 to 101 volts. 

Accuracy also identifies the amount of uncertainty present in the measurement concerning the relevant absolute standard. It could be determined in numerous ways and is highly reliant on the specification philosophy of the product design and supplier. 

Many accuracy specifications involve an offset and gain parameter. The former is normally displayed as an absolute amount like ohms or volts, and they’re independent of the input’s magnitude. Normally, gain errors vary on the input’s magnitude and are displayed as a percentage of the reading.

  • Sensitivity

Sensitivity is considered as the absolute quantity, while the resolution is the relative quantity. Thus, it describes the tiniest absolute amount of change, which can be sensed by a measurement, often shown in microohms, millivolts, or tenths of a degree.

Please take note that sensitivity must not be confused along with accuracy as they are completely different parameters. For instance, a device quantified with 1-mV sensitivity might be accurate to 10 mV along with an applied input of 10 V. 

However, the device could still observe the difference if the 10-V input signal was adjusted by one mV. Bear in mind that sensitivity often can be enhanced through averaging.

How Do You Calculate a Digital Multimeter’s Resolution? 

As mentioned earlier, the resolution is a crucial factor in measuring uncertainty and accuracy. You may not know it yet, but the resolution was specified in terms of the number of digits shown. Therefore, they will be composed of an integer and a half number such as 3 ½. If you convert a half digit, it can be either displayed as one or zero. 

The conventional format for quoting the digit’s digit resolution might not be suitable for most new digital multimeters. That’s especially true for virtual instruments where the display is controlled by software and thus not a limiting factor. As an alternative, the limiting factor is the analog to digital converter, ADC.

The resolution of such instruments and devices is often displayed in bits. For instance, a 14-bit ADC would present 2^14 distinct values, 16384 values. 

Would you like to know how you can calculate the resolution of your digital multimeter? You can use this formula: digits of resolution = log (number of LSB). For example, let’s say the log to the base is ten. That implies the least significant bit for a digital multimeter with a 14-bit ADC is 16384. 

Final Thoughts

Many types of equipment these days have become more powerful and complicated at the same time. So have the digital multimeters. Wireless test tools can deliver results to one another and smartphones to share notes, pictures, and other digital data with other people.

Wireless digital multimeters, smartphone apps like the Fluke Connect, and other related test tools enable electricians and engineers to make the best choices more efficient and faster than ever before. That helps in saving a huge amount of time and boosting their productivity. 

Every time you plan to purchase a digital multimeter, always make sure its resolution and accuracy are enough. Remember that those figures suggest that the test instrument offers a figure far above what may be required.

In situations where the real value is essential, you should guarantee both the resolution and accuracy meaning the meter’s reading is accurate enough and has an adequate resolution.

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