When working with an oscilloscope, selecting the right probe is just as important as choosing the right oscilloscope itself. A probe is the crucial link between your device under test (DUT) and the oscilloscope, allowing you to accurately capture signals and analyze them in real-time. With so many types of probes available, it can be overwhelming to choose the correct one for your specific needs.

In this blog, we'll walk you through the key factors to consider when choosing a probe for your oscilloscope, discuss the importance of probes in testing, and provide examples with UNI-T's oscilloscope and probe range.

Key Factors to Consider When Choosing a Probe for Your Oscilloscope

1. Bandwidth

The bandwidth of a probe refers to the range of frequencies it can measure accurately. When choosing a probe, you need to ensure that its bandwidth is higher than the frequency of the signal you're measuring. If the bandwidth of the probe is too low, it may not capture the signal accurately, resulting in distortion or loss of critical information.

For example, if you're using a UNI-T MSO7204X oscilloscope, which has a bandwidth of 2 GHz and a sample rate of up to 10 GSa/s, you would need a probe with at least 1 GHz of bandwidth to fully utilize the oscilloscope's capabilities. UNI-T's UT-P07 (500 MHz bandwidth) would be an appropriate choice for high-speed signals, while the UT-P04 (100 MHz) may be sufficient for lower-frequency signals.

2. Probe Attenuation

Probe attenuation is the ratio of the signal the probe measures to the signal it actually displays on the oscilloscope. It is typically expressed in a ratio, such as 10:1 or 100:1. Probes with higher attenuation ratios reduce the voltage level of the signal, making it easier to measure high-voltage signals safely without overloading the oscilloscope's input.

For example, the UT-P01 is a 10:1 probe with a maximum voltage rating of 600 Vpp, which is ideal for typical measurements where the signal is within this voltage range. For higher voltage measurements, such as in power electronics, the UT-P20 (100:1 attenuation and 1500 V) is more suitable for safely handling high-voltage signals.

3. Maximum Voltage Rating

The maximum voltage rating of the probe indicates the highest signal voltage it can measure safely without damaging the probe or the oscilloscope. Ensure that the voltage rating of the probe is greater than the voltage of the signal you intend to measure.

For example, if you're working with high-voltage signals, you might consider probes like the UT-P21 (high-voltage passive probe with a 1000:1 ratio and a maximum voltage rating of 15 kVrms for DC and 10 kV for AC sine wave) for safe and reliable measurement.

4. Differential Probes

Differential probes measure the voltage difference between two points on a circuit, making them ideal for applications where you need to measure signals that don't have a common ground. For example, UT-P30 and UT-P31 are differential probes that allow you to safely measure high-voltage differential signals in circuits such as those used in automotive or power systems.

Differential probes like these are essential when testing floating circuits or isolating certain signals without connecting to a ground reference.

5. Current Probes

Current probes are designed to measure the current flowing through a conductor. These probes typically use a clamp-on design to detect the magnetic field produced by current flow. UNI-T's UT-P40, for example, is a current probe with a conversion ratio of 50mV/A and a frequency range of DC to 100 kHz, suitable for measuring current in a wide range of applications.

6. Probe Type: Passive vs. Active

• Passive probes are the most commonly used probes and are suitable for most general-purpose measurements. These probes are ideal for low-frequency signals and are usually cheaper than active probes.
• Active probes are used for high-speed or high-frequency signals and are designed to minimize loading effects on the circuit under test. These are more expensive but necessary for high-performance oscilloscopes like the MSO7204X for capturing fast signals.

7. Ease of Use

Consider features like flexible cable lengths, ergonomic design, and ease of connection to the oscilloscope and DUT. Some probes, like the UT-P05 and UT-P06 come with flexible, long cables that make them suitable for use in tight spaces or when measuring large devices.

Importance of the Probe in Testing

The probe is the most critical part of your measurement setup. Without a proper probe, you could miss vital information in the signal or introduce errors due to incorrect voltage or bandwidth limitations. A high-quality probe ensures:

• Accurate measurements: Capturing the correct waveform and characteristics of your signal.
• Signal integrity: Minimizing the effects of the probe on the signal you're testing, especially for high-speed signals.
• Safety: Ensuring that high-voltage signals can be measured safely without damaging the equipment or putting the user at risk.

Example: Choosing the Right Probe for UNI-T Oscilloscopes

Choosing the correct probe for your oscilloscope is crucial to ensure accurate measurements and to maximize the full capabilities of your test equipment. Here are more detailed examples to help you understand the factors to consider when selecting a probe:

1. Basic Oscilloscope Measurement:

Example: MSO2204X Oscilloscope with a UT-P04 Probe

• Scenario: You’re working with high-frequency signals at up to 100 MHz and need to measure a 5V peak-to-peak signal.
• Oscilloscope: The MSO2204X offers 200 MHz bandwidth and a maximum sampling rate of 5 GSa/s, which is well-suited for capturing high-frequency signals.
• Probe: The UT-P04 (10:1) probe, with 100 MHz bandwidth and 600Vpp voltage rating, provides accurate results for this setup.
• Why this combination works: The UT-P04 probe ensures that you can measure signals within the bandwidth of the oscilloscope while maintaining signal integrity, avoiding any attenuation or distortion due to insufficient probe bandwidth.

2. High-Voltage and High-Frequency Measurement:

Example: MSO7104X Oscilloscope with a UT-P21 Probe

• Scenario: You need to test a high-voltage AC signal with a peak voltage of 12kV.
• Oscilloscope: The MSO7104X has a 1 GHz bandwidth, which is ideal for fast-changing signals, as well as high sampling rates.
• Probe: The UT-P21 is a high-voltage passive probe with a 1000:1 attenuation ratio and 50 MHz bandwidth, which allows it to safely measure voltages up to 15kVrms (AC) and DC 15kV.
• Why this combination works: The UT-P21 probe's high voltage handling and its ability to attenuate the signal by a factor of 1000 ensures that you can safely measure very high voltages without damaging the oscilloscope. The bandwidth of the probe is also suitable for slower-changing high-voltage signals.

3. Differential Measurement of High-Speed Signals:

Example: MSO7204X Oscilloscope with UT-P32 Probe

• Scenario: You need to measure differential signals in a high-speed data transmission system with 1.5V peak-to-peak differential voltage.
• Oscilloscope: The MSO7204X, with a 2 GHz bandwidth and a maximum sample rate of 10 GSa/s, is ideal for fast signals and provides the necessary resolution and accuracy.
• Probe: The UT-P32 is a differential probe with a bandwidth of 50 MHz and differential voltage capability of ±3000Vpp.
• Why this combination works: The UT-P32 is designed for differential measurements, which is essential for accurately capturing and measuring two related signals, such as the positive and negative parts of a differential signal. This allows you to precisely view the relationship between the two signals on the oscilloscope.

4. Low Current Measurement:

Example: MSO2202 Oscilloscope with UT-P40 Probe

• Scenario: You need to measure low-current waveforms from a power circuit operating with small current ranges up to 1A.
• Oscilloscope: The MSO2202 provides a 200 MHz bandwidth, suitable for low-frequency signals and detailed waveform analysis.
• Probe: The UT-P40 current probe offers a conversion ratio of 50mV/A and works within a current range of 0.4A to 60A, with a frequency range of DC to 100 kHz.
• Why this combination works: The UT-P40 current probe provides accurate current measurements in low-power circuits while maintaining signal integrity at higher frequencies, making it ideal for power electronics testing.

5. General-purpose Testing:

Example: MSO3034HD Oscilloscope with UT-P03 Probe

• Scenario: For general-purpose signal testing of low-frequency analog and digital circuits.
• Oscilloscope: The MSO3034HD offers 350 MHz bandwidth, which is suitable for a variety of signal types.
• Probe: The UT-P03 probe, with a 60 MHz bandwidth and 600Vpp voltage rating, is perfect for general-purpose testing where high-frequency signals (up to 60 MHz) are being used.
• Why this combination works: The UT-P03 probe, with its 10:1 attenuation ratio, ensures that the probe is well-matched with the oscilloscope’s bandwidth for reliable and clear signal measurements.

6. High-Frequency and Low-Voltage Testing:

Example: MSO3504E-S Oscilloscope with UT-P06 Probe

• Scenario: You are working with high-frequency signals up to 300 MHz in an RF testing environment.
• Oscilloscope: The MSO3504E-S has a 500 MHz bandwidth, making it ideal for high-frequency signals like RF or digital pulses.
• Probe: The UT-P06 probe, with a 300 MHz bandwidth, is designed to accurately capture and display high-frequency signals with a 600Vpp voltage rating.
• Why this combination works: The UT-P06 probe complements the high-speed MSO3504E-S oscilloscope, allowing you to capture fast transient signals with high fidelity without losing accuracy due to bandwidth limitations.

Conclusion: Which Probe Should You Buy?

When selecting a probe for your oscilloscope, always consider:

• The bandwidth needed for your signals.
• The voltage level of the signals you're measuring.
• The attenuation ratio required for safe and accurate measurements.
• Whether you need a differential or current probe for specific measurements.

By understanding these factors, you can choose the best probe for your oscilloscope, ensuring accurate and safe measurements for your testing needs.