How to Test Multimeters
The accuracy of a Digital MultiMeter (DMM) is listed on the bottom of the meter. It is given as a reading percent + number of least significant digits, such as ± (1% + 1 Digit). To use this accuracy description, do the following: (1) Multiply the reading displayed on the meter by the percent accuracy. Secondly, what does counts mean on a. Nov 27, · Accuracy can also be measured by the count of digits added to the basic rating. For example, an accuracy of +/- (2% +2) means that the multimeter may show readings between V and V for a V measurement. Highly accurate DMMs such as those by Fluke can give a basic DC accuracy range between % and %.
For the best electrical and electronic test results, it is necessary to check the accuracy of a Digital Multimeter DMMas defined by the manufacturer. This becomes important for test engineers who also need to know how to best interpret results on their DMMs. The accuracy and precision of modern multimeters are well beyond the requirement for most applications.
However, it is recommended that you ot both these parameters in detail for more mu,timeter tests. The launch vehicle and satellites fell back to earth before burning up in the atmosphere. As a result, seven commercial satellites were destroyed. Test and measurement etst, even DMMs, with higher accuracy are needed for specialized industries such as space technology, electronics, medical equipment, and defense manufacturing and testing.
In such cases, high repeatability of test accugacy, high accuracy, and resolution are crucial. For less critical applications such as day-to-day troubleshooting electronic tesgDMMs with medium accjracy can be used. Such devices are comparatively less expensive. Every DMM manufacturer displays both accuracy and precision in mmultimeter manuals but their exact meanings can be confusing for many. Accuracy is displayed as a percentage of the largest allowable error. It indicates the variation of the measured value from the actual value how to download igi 2 game certain operating conditions.
The measured value is then vetted against the industry-standard acceptable for that parameter and Device Under Test DUT. The higher the accuracy, the closer the result of a DMM would be to the actual value. Some industries could accept this benchmark, others may not.
Accuracy can also be measured by the count ro digits added to the basic rating. Precision is defined as the ability of a digital multimeter to show the test reading within the defined accuracy limit repeatedly.
In simple language, this can be correlated to the bullet holes on a shooting-range target. If the attempts made are close to each other but outside the bullseye, it can be called precise but not multimeher. However, if all the holes are in the bullseye, it is both mulgimeter and precise.
In electrical testing terms, a multimeter that can measure a The DMM you choose fo have the right combination of accuracy and precision that best suits your industry applications. Next, remember to not assume that multimeter readings are close to the true value. The LSD lets ot determine the magnitude of uncertainty caused due to noise, rounding what is a dilute calico cat, and tp offsets.
Accuracy and range need to be considered independently to avoid gross errors. For example, how should you interpret the true voltage of 1. You should strive to select the lowest possible range in which the DMM gives accurate results without showing overload.
While accuracy and precision are important, they are affected by other parameters. Resolution: It is the smallest change in measurement at the lowest range setting that the DMM can detect and display. Clearly, DMMs with higher resolution show higher accuracy. Range: Range and resolution are related terms. Wccuracy range is defined as the minimum and maximum reading that a DMM can measure for a parameter before it shows overload OL.
Many advanced DMMs set a range automatically depending upon the magnitude of test measurements. Higher accuracy is achieved when a DMM can show test results in a narrow range without going in OL state.
For example, a Three full digits range between 0 and 9, and half digit varies between 0 and 1. Modern DMMs accuarcy classified on counts rather than digits. A higher count denotes better resolution. Altitude, temperature, and humidity: Like most other electronic devices, multimeter accuracy can also be affected by temperature variations. The manufacturer usually defines a temperature coefficient in DMMs specifications. Humidity and altitude are also defined in a range for most DMMs beyond which they cease to give accurate hoow.
The UA model has an operational altitude of hoow, m. It is important to check these specifications and compare them with the ambient temperature, humidity, and altitude of the location where the DMM will be used. If you go beyond these specifications, the display may become sluggish, go blank, or show ghost images.
Component tolerance, noise level, and stability of internal references: Finally, the accuracy also depends greatly on the acfuracy of components used inside the DMM. Components with high tolerance to external factors such as shock due to drop and electronic noise can give higher accuracy.
While high-precision benchtop DMMs can be very expensive, they have very specific requirements. In most cases, handheld models can meet regular test needs. An ideal tradeoff multimetre the tst and specifications is important for business, and you can find well-performing digital multimeters online for rent or sale.
The practical tips in this article to understand and check digital multimeter accuracy can help with correct measurements for your application and when you need to buy your next multimeter. Save my name, email, and website in this browser for the next time I comment.
Sign in. Log into your account. Forgot your password? Password recovery. Recover your password. Get help. Better Tech Tips. By Editorial What did i go wrong. Updated: November 27, How Is Precision Different from Accuracy?
Scenario 1: Set the meter to how to use gundam marker V range. The reading will not even be displayed because only one digit after the decimal is shown. The percentage reading is calculated as 1. Tedt meter will display the value between 1. Any reading between 1. Now what does a human resources do range is between 1.
Factors That Affect Digital Multimeter Accuracy While accuracy and precision are important, they are affected by other parameters. Conclusion While high-precision benchtop DMMs can be very expensive, they have very specific requirements. Tags hardware how to. You have an incredible home and also a very amazing collection of clothes that you are emotionally attached to and refuse to part with Read more.
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What Are the Applications of a Multimeter?
Oct 18, · Accuracy may also include a specified amount of digits (counts) added to the basic accuracy rating. For example, an accuracy of ±(2%+2) means that a reading of V on the multimeter can be from V to V. Use of a digital multimeter with higher accuracy allows for a great number of applications. Apr 24, · Set the multimeter to the correct factor of 10; set the multimeter to the ? mark to test a resistor known to be a ? resistor, for instance. Place one probe at each end of the resistor. Check the display to make sure it shows a value very close to the resistor value. At least one of those meters is badly off. What you need is a reference voltage.A good starting point would be the LT, which should cost you about 4 dollars plus shipping from Digikey. This will give you a 5 volt output with an accuracy of %. If this is too much for you, a TL will cost 40 cents, but its accuracy will only be 1%.
If you are not sure how accurate your digital multimeter measurement is, find its accuracy specifications in the instruction manual, and then read this to get the rest of the story. Most hand-held DMMs are more accurate than you might expect, including the least expensive models.
In addition to volts, ohms, and amperes, many can also measure frequency and capacitance. The accuracy of an electronic measurement defines how close the indicated value is to the true value of the measured signal. Analog meters usually have their accuracy listed as a percentage of the full-scale reading. However, the further away the reading is from full scale, the greater it can deviate from the true value when viewed as a percentage of reading, not as percentage of full scale. Based on this accuracy, its pointer can be 3 volts V x 0.
If the true measured value is, for example, However, Compared to analog meters, digital multimeters DMM have many practical advantages. They present measurement data in a direct format that does not require calculating the exact value, and they are free from the parallax error of analog meters.
Unlike meter movements in analog meters, digital multimeter displays have no moving parts, and they are free from wear and shock failures. DMMs automatically detect polarity, show positive and negative values, have much better overload protection, and offer automatic as well as manual range selection options.
All these features lead many DMM users to believe that because the meter displays the measured value in direct decimal format the number shown is the true value of the measured parameter.
However, to calculate the actual deviation from the true value that the meter manufacturer can claim and still be within specifications requires a much deeper understanding of the published electrical meter specifications. For example, first, look at how DMM resolution and ranges affect accuracy, then read the examples that follow and learn what the meter manufacturers really mean. They are also known as count DMMs. DMM resolution depends on the maximum number of analog-to-digital converter ADC counts during a full conversion.
However, a practical resolution also accounts for the number of least significant counts — similar to the accuracy rating. Typically, dc voltage measurements use the full count capability of the ADC, since signal conditioning is rather straight forward: it uses resistive dividers and filters. Other functions might be limited in range or require signal conditioning that limits the ADC input range and gives a coarser resolution.
Many DMMs temporarily blank the leading digit when it contains a zero. The larger number of counts should translate into higher resolution, and usually DMMs with a higher resolution have higher accuracy. However, DMM accuracy also depends on other design factors, such as ADC accuracy, component tolerances, noise level, and the stability of internal references.
In addition, since DMMs have automatic polarity detection, they display negative values equal in range to the positive values. Ranges Select the highest range first to keep the meter safe from damage, then switch to progressively lower ranges to obtain the most accurate measurement available on a given meter.
Range selection on the least expensive DMMs is usually manual: the user sets the rotary switch to the appropriate range of the desired function. The top range is limited by the maximum voltage that the meter can safely handle.
For manual range-changing meters, switch to a range that provides the maximum number of digits for the unknown voltage. For example, when measuring a 1. Switching to the V range will show 1. This will become more obvious in the following section on DMM accuracy.
However, basic accuracy does not take into account the inner workings of the ADC that is at the heart of every DMM and other circuitry on the analog side. These circuits and the ADC have tolerances, nonlinearities, and offsets that vary from function to function. In addition, signal noise might require limiting the resolution. To give meter users a more accurate value, DMM manufacturers present accuracy specifications in the following format:.
The LSD represents the magnitude of uncertainty due to internal offsets, noise, and rounding errors. For a given DMM the number of LSDs varies from function to function and even from range to range for the same function. Accuracy and range selection need to be considered independently, otherwise a misunderstanding can lead to gross errors.
For example, consider the following:. Presume that the true voltage is 1. How should you measure the voltage and interpret the reading? First, set the meter to the V range. The display will indicate the measured voltage as XX. The percentage of reading is 1. So, the meter can display a value of 1.
Set the switch to the V range and it will display the value as X. XX, which improves the accuracy. So, any reading between 1.
Finally, set the DMM to the 2-V range. The display format changes to X. The percentage of reading does not change, but the third LSD becomes a smaller factor. The meter display is only allowed to be within the narrow 1. So, selecting the lowest measurement range before the DMM over-ranges reduces the negative effect of the number of LSDs and gives the most accurate results.
Time, temperature, and humidity When was your meter manufactured or recalibrated? Most meter manufacturers and calibration services guarantee accuracy specifications only for one year. After that, the DMM might not keep its accuracy within published limits. So, if accuracy must be guaranteed, the meter must be calibrated about once a year. The most accurate reading for a digital meter is in the lowest range that shows the most significant digit in the left-most position. Select the lowest measurement range on the DMM before it over-ranges to read the most accurate results.
For example, in the first figure, a DMM reads an unknown low voltage which appears to be 1. Initially, the reading looks acceptable. However, switching to the V dc range improves the accuracy; the reading is now 1. Finally, after switching the DMM to the 2-V dc position, the reading is 1. It then becomes obvious how the LSD counts can become a more significant source of error than the accuracy when the range selection is not considered. Do not use the meter when the ambient temperature is higher or lower than the specified operating temperature range.
In addition to the operating temperature specifications of electronic components inside the meter, LCD displays are notorious for becoming sluggish and eventually going blank at subfreezing temperatures. At high temperatures, LCDs display ghost images of the segments that are turned off, and they eventually darken. This wide temperature range guarantees that the meter will perform reasonably well under most indoor and outdoor conditions. Do not confuse the operating temperature with the temperature range at which the manufacturer specifies meter accuracy.
Some meter specifications list a temperature coefficient value that helps calculate the accuracy of a specific function for the entire operating temperature range. A typical example of a temperature coefficient would be 0. However, do not assume that every meter will have the same temperature coefficient. If the meter manual does not list it, the loss of accuracy due to ambient temperature fluctuations might be much higher.
Also, the effect of humidity increases at a higher temperature. Discuss this on the Engineering Exchange:. A second sensor, having the same measuring range, respectively has an error of 0. John, Thx for sharing this article. Your analysis is flawed. The total error is the stated tolerance at full scale, however any reading below F.
In your example of 90V value that is 0. To recap the bounded error is a scaled value of the F. To simplify the subject I have left out the LSD, temp co, noise, humidity etc. The part that slays me is a meter that has counts but only has 0. Essentially they are selling a 3. Again, hope this clarifies the F. You may also like: Troubleshooting VFDs — with no-power checks Where to get free training in electronics and instrumentation How to select an oscilloscope Digital troubleshooting with logic probes and logic pulsers.
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