- Common Reasons for Incorrect Readings
- Troubleshooting Digital Oscilloscope Readings
- Calibrating a Digital Oscilloscope
- Environmental Factors Affecting Readings
- User Errors Impacting Accuracy
- Tips to Ensure Accurate Measurements
- Conclusion
- Frequently Asked Questions
Your digital oscilloscope might read something inaccurate for a variety of reasons including lack of calibration, signal disruption, or probe settings. Calibration adjusts the device to known quantities so that it reads accurately.
At the same time, nearby electronic devices or bad grounding can introduce interference signals. Incorrect probe settings, like mismatched impedance or an unsuitable attenuation ratio, can further corrupt the data.
Environmental conditions such as temperature or humidity could play a role in performance if the product is used outside the recommended environmental conditions.
Old firmware or just software bugs in general can mess with a measurement. This can be avoided by keeping the oscilloscope well calibrated and properly configured.
Knowing its specifications will get you on the road to realizing dependable performance in your testing and measurement application.
Common Reasons for Incorrect Readings
Digital oscilloscopes (DSOs) are wonderful tools for troubleshooting electronic circuits, but they often give you wrong readings. This is usually the result of a tragic confluence of user configuration, hardware restrictions, and use case driven design choices. Awareness of these issues is the first step to troubleshooting and ensuring more accurate measurements.
Incorrect Probe Settings
The settings on your probe are an important factor for measurement accuracy. If your probe’s attenuation setting is different than what is configured on the oscilloscope, you’ll start to observe erroneous voltage readings. This discrepancy can cause false readings.
A 10x probe not set correctly on the oscilloscope may show values ten times higher or lower than the actual signal. Tip 7 – Make sure your probe’s attenuation is set to the oscilloscope’s input setting.
Poor Grounding Connections
Incorrect grounding can create noise that results in corrupt waveforms. High-frequency signals are particularly prone to interference from ground loops or lengthy ground leads.
Using a short, direct ground connection can go a long way toward reducing noise and improving signal integrity. As an example, ground spring adapters offer a more stable connection than typical alligator clips.
Faulty or Damaged Probes
Probes go bad after extended use. Damaged tip, broken cable, or worn connections can lead to false signals or incorrect readings.
Check probes on a regular basis for wear and replace probes accordingly.
Improper Input Coupling Selection
DSOs provide coupling solutions (DC, AC, or ground). If you select the incorrect setting, you risk filtering out useful portions of your signal.
For example, if you use AC coupling on a signal that has DC components, you will block the DC offset. Always couple as closely as possible to your measurement needs.
Outdated Firmware Issues
Bug fixes released through firmware updates can impact accuracy. An obsolete oscilloscope will not produce accurate readings, even with perfect hardware settings.
Visit the manufacturer’s website to look for updates and install them regularly.
Troubleshooting Digital Oscilloscope Readings
Digital oscilloscopes are incredibly useful for visualizing waveforms and diagnosing problems, but misleading readings can sabotage their power and usefulness. If you want to get it right, the key is working through what could be wrong in a systematic manner.
1. Check Probe Connections
Another very frequent culprit for wrong readings is loose or bad probe connections. Make sure the probe is properly connected to both the oscilloscope and your point of test.
Inspect the ground clip as well since a bad connection can add noise or alter the signal as well. For example, if measuring a 5V DC signal, a loose connection will show random values bouncing around.
Properly using good quality probes and checking for probe integrity can avoid these kinds of discrepancies.
2. Verify Oscilloscope Settings
Setting things up wrong can cause you to get very misleading measurements. Make sure to verify your voltage range, time base, and coupling mode (AC or DC).
If you’re measuring a DC signal and the coupling is set to AC, your waveform will appear jumbled. This occurs because of the mismatch in sample and hold settings.
It increases accuracy greatly, especially when manually adjusting the channel offset. This is extremely important because nearly all oscilloscopes are limited to 8-bit ADCs, setting a hard ceiling on resolution.
3. Test with Known Signals
Testing the oscilloscope with a known good signal, such as the built-in calibration source, can reveal mistakes.
If the waveform shown is still far off from what you were expecting, there’s an even larger chance that the problem is with the oscilloscope.
4. Inspect and Replace Probes
Using damaged probes can greatly affect the readings. Check your probes for any signs of wear or damage, especially at the tip and the cut of the cable.
Sometimes replacing old and faulty probes can do wonders for properly capturing the signal in question.
5. Update Firmware Regularly
Glitches or inaccuracies can stem from outdated firmware. Firmware updates typically provide performance fixes and bug corrections, so you’ll always get the best performance and most stable oscilloscope.
Calibrating a Digital Oscilloscope
Calibrating a digital oscilloscope is an important step in ensuring you will get the most accurate signal measurements. An oscilloscope’s primary function is to display signals. Calibration adjusts the inner workings, making sure the device provides the most dependable data possible. Just a small calibration error can cause your state-of-the-art oscilloscope to return confusing results, affecting your analysis.
Use Built-in Calibration Tools
Fortunately, most new digital oscilloscopes include built-in calibration tools that make the process easier than ever. These tools allow you to check and adjust the instrument’s accuracy by comparing its readings against a stable reference signal. For instance, general-purpose scopes, which are often 8-bit, can take advantage of this feature to preserve precision.
Issues like low voltage levels might occur if the probe is set to a 1:10 position, making calibration even more critical. High-end scopes such as Keysight’s Infiniium UXR series can easily be priced at more than $1 million. They are based on the same calibration processes used by cheaper models, like Rigol scopes. This emphasizes the widespread need for calibration, even with low-cost devices or those with advanced capabilities.
Adjust Vertical and Horizontal Scales
True calibration means adjusting both vertical and horizontal scales so that they align with the signal’s characteristics. The vertical scale controls voltage ranges and the horizontal scale controls time intervals. Not having this alignment can lead to waveform distortion or wrong measurements.
Lower-cost digital storage oscilloscopes (DSOs) usually use different paths for high and low frequencies. This design is very sensitive and needs to be calibrated carefully in order to work well. If you see signs of incorrect operation, like a wiggling low-frequency signal, returning to these settings to double-check them is a good idea.
On a 6.5-digit digital multimeter (DMM), faster sampling speeds can result in lost accuracy. This is a great example of the need to make periodic course corrections.
Follow Manufacturer Calibration Guidelines
To have them perform at their best, every oscilloscope manufacturer gives you detailed calibration instructions. These guidelines are supplemented by detailed, step-by-step instructions based on the design and features of the specific device. Certificates of calibration that are compliant with international standards (like ISO/IEC 17025) provide added peace of mind in terms of accuracy and reliability.
Following these guidelines will make sure your oscilloscope is an ever-reliable tool in your arsenal of signal analysis. General-purpose scopes will never be able to reach the precision and bandwidth of specialized instruments. If you’re regular with the proper calibration procedures, you can improve their performance considerably.
Environmental Factors Affecting Readings
Digital oscilloscopes are very sensitive instruments that need stable outside conditions in order to guarantee accurate readings. If environmental factors are not accounted for, readings can be affected and produce false readings, resulting in misinterpreted data. Here are major environmental factors affecting readings and practical tips to help recognize and mitigate such issues.
Temperature and Humidity Variations
Changes in temperature and humidity can even affect an oscilloscope’s internal components, such as capacitors and resistors, changing their performance. High humidity can result in condensation forming within the device, which can create short circuits or heightened noise that could affect readings.
For instance, a lab that is in a very humid environment and does not have enough dehumidification may see random spikes in measurements. Keeping a controlled environment, preferably between 68°F and 77°F with humidity under 60% creates a consistent baseline for readings.
Electrical Noise Interference
Electrical noise is a common interloper in environments saturated with electronic devices. Electromagnetic interference (EMI) from equipment such as switched-mode power supplies can radiate into oscilloscope analog circuits, creating a dipole antenna.
Although isolators are often used, parasitic coupling can often still reduce the Common-Mode Rejection Ratio (CMRR), especially at high frequencies. Shielding the oscilloscope and proper grounding (e.g., connecting to a Protective Earth) reduces this interference.
Keep in mind, scopes with floating chassis or ungrounded scopes present safety hazards and measurement errors.
Improper Workbench Setup
A messy and distracting workbench can lead to mistakes in measurement. Scopes with poor electromagnetic shielding are susceptible to high-frequency noise, especially if grounded return paths are not taken into account.
For example, if unprotected ground clips on probes inadvertently touch hazardous voltages, the safety of the user and the protection of the equipment could be compromised. Insulated coax connectors and plastic covers over exposed metal parts minimize these hazards.
User Errors Impacting Accuracy
Digital oscilloscope incorrect readings are most commonly attributed to user errors. Oscilloscopes are great tools, but accuracy is largely determined by the user. User errors such as mistakes when interpreting waveform displays, configuring trigger settings, or even just considering bandwidth limitations can all lead to inaccurate data. By recognizing these common pitfalls, you can help increase your accuracy.
Misinterpreting Waveform Displays
While waveform scopes show a convenient visual display of your signals, they are not definitive measurements. In contrast to a digital multimeter (DMM) or frequency counter, an oscilloscope favors visualization over precision. The waveform might appear pretty clean, but minor user errors—such as not zeroing out offsets—will introduce accuracy errors and cause assumptions to be made.
For example, you should make sure that the ground position is clearly visible on-screen. If it is, short the input, measure the zero offset, and subtract it out of your results. This removes offset inaccuracies without creating undue complexity. First and foremost, remember that the 3% accuracy in the spec sheet doesn’t paint the entire picture. To obtain a realistic estimate for the error margins you need to use Gaussian error propagation.
Incorrect Trigger Settings
Incorrect trigger settings can lead to unstable waveform display and inaccurate readings. A poor fit between the trigger level and the true range of the signal can lead to data that’s often inaccurate or truncated. Specifically, if the trigger level is set too high on a low-amplitude signal, you end up missing the peaks and can’t synchronize correctly.
While manufacturer guidelines are useful, having an instrument that you know to be accurate, such as a power meter, is a great way to cross-reference that information. Even small parameter changes, such as calibration to the nearest 1/10th of a division, can make dramatic improvements.
Overlooking Bandwidth Limitations
If you’re using an oscilloscope in the development process, you’re likely familiar with the concept of bandwidth limitations. Signals above this threshold are clipped or otherwise distorted, resulting in erroneous data. Users tend to forget this, thinking that the scope will be able to deliver all the signals at the same level.
Be aware that lies are commonplace in specifications, especially when it comes to ADC/DAC performance. We found that comparing the scope with another trusted device, which is often possible, helped corroborate or disprove claims. As an example, if the bandwidth is 100 MHz, signals at or close to this should be treated with extreme care.
By being aware of these limitations, you can avoid getting a false analysis, while still pushing the oscilloscope to its full potential.
Tips to Ensure Accurate Measurements
Getting accurate measurements on your digital oscilloscope involves careful consideration and the right care and feeding. If there are small oversights, such as mismatched measurement settings or lack of regular maintenance, it can throw your results off. Here are some concrete steps to help ensure accurate, reliable measurements.
Use High-Quality Probes
This is because the quality of the probes directly affects the precision of your measurements. Always use probes that are compatible with the oscilloscope’s specifications such as 10X or 1X attenuation settings.
Be sure to check that these settings match on both the probe and the device. For adjustable probes, make sure they are compensated correctly by checking with the oscilloscope’s built-in calibration signal. An underdamped probe can clip the waveform.
Additionally, make sure that the BNC connectors are properly seated, as they should click into place in order to provide a solid connection.
Regularly Clean Connections
Any dust, oil or oxidation on a connector or contact can lead to added distortion or noise in the signal path. Frequent cleaning of probe tips, BNC connectors, and oscilloscope input terminals with isopropyl alcohol will help maintain a good connection for accurate signals.
Even minute particles can scatter the signal flow, causing discrepancies within the results.
Maintain Proper Storage Conditions
Keep your oscilloscope in a clean, dry place to avoid internal contamination, which can lead to deterioration over time. Heat, humidity, and dust can all negatively impact sensitive components such as ADCs (analog-to-digital converters), which already have very tight accuracy margins.
Routinely releasing firmware updates ensures they continue to work at the highest level.
Conclusion
Digital oscilloscopes are incredibly useful devices, but minor user mistakes can result in misleading or incorrect readings. Knowing issues such as calibration errors, environmental changes, and user errors goes a long way to preventing frustration. Regular maintenance and smart setup go a long way in ensuring you get the most accurate measurements. Stay mindful of things such as the probe’s attenuation settings, excessive signal noise, and rapid temperature changes and you’re bound to achieve the most accurate results time after time.
Focusing energy on troubleshooting and calibrating up front pays dividends later. By remaining proactive and adhering to proper protocol, you can rely on your oscilloscope to provide the most accurate information possible.
If you’re still having trouble, refer to your device user guide or contact a qualified professional for assistance. Don’t let little issues get in your way — learn how to tune up your workflows and get more done with ease right here, starting today.
Frequently Asked Questions
Why is my digital oscilloscope showing incorrect readings?
Improper calibration, user errors, and environmental factors such as temperature and electrical interference are common causes of incorrect readings. Make sure you’re not making rookie mistakes by double-checking your settings and connections and making sure your device is calibrated properly.