Tektronix PRIMER P6101B Manual

Abcs of probes

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ABCs of Probes

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Page 1 ABCs of Probes –– PRIMER...
Page 2 Simply contact your Additionally, be sure to review the following safety precautions local Tektronix representative or visit www.tektronix.com. to avoid personal injury and to prevent damage to the measuring equipment or the systems to which it is attached.
Page 3: Table Of Contents
Maximum Input Current Rating (current probes) ....44 Maximum Peak Pulse Current Rating (current probes) ..44 Maximum Voltage Rating (universal) ........44 Propagation Delay (universal) ..........44 Rise Time (universal)............45 Tangential Noise (active probes) ........45 Temperature Range (universal) ........45 Threshold Voltage (logic) ..........45 www.tektronix.com/accessories...
Page 4: Precision Measurements Start At The Probe Tip
Figure 1.1, where the probe is indicated as an undefined box signal in any way or changes the way a circuit operates, the in the measurement diagram. oscilloscope sees a distorted version of the actual signal. The result can be wrong or misleading measurements. www.tektronix.com/accessories...
Page 5: The Ideal Probe
Often, this probe tip is in the form of a spring-loaded hook that allows you to actually attach the probe to the test point. www.tektronix.com/accessories...
Page 6 The external device acts as a load when it draws signal current from the circuit (the signal source). This loading, or signal current draw, changes the operation of the circuitry behind the test point, and thus changes the signal seen at the test point. c. Clamp-on current probe. www.tektronix.com/accessories...
Page 7: The Realities Of Probes
It’s important to be further. aware of these limitations and their effects when selecting and First, it’s important to realize that a probe, even if it’s just a using probes. simple piece of wire, is potentially a very complex circuit. www.tektronix.com/accessories...
Page 8 If you use a probe that is not on the oscilloscope’s recommended list of probes, you run the risk of unpredictable measurement results. www.tektronix.com/accessories...
Page 9 This places a load at the test point that can change = 5,000,000 V/50,100 the signal that the circuit, or signal source, delivers to the test = 99.8 V point. www.tektronix.com/accessories...
Page 10 However, there are also probes that allow you to sense phenomena other than voltage signals. P6101B 1 MΩ 100 pF P6109B 10 MΩ 13 pF P6139A 10 MΩ 8 pF P6243 1 MΩ ≤1 pF Table 1.1. Probe capacitance. www.tektronix.com/accessories...
Page 11: Some Probing Tips
Moreover, the realities of probes discussed above also them to the oscilloscope and check compensation frequently. extend down to the transducer. Transducers have bandwidth limits as well and can cause loading effects. www.tektronix.com/accessories...
Page 12 6.5 inch probe ground lead. 28 inch lead attached to probe lead. Figure 1.13. Extending the length of the probe ground lead can cause ringing to appear on pulses. Also, it’s wise to check probe compensation whenever you change probe tip adaptors. www.tektronix.com/accessories...
Page 13: Summary
In this first chapter, we’ve tried to provide all of the basic information necessary for making appropriate probe selections and using probes properly. In the following chapters, we’ll expand on this information as well as introduce more advanced information on probes and probing techniques. www.tektronix.com/accessories...
Page 14: Different Probes For Different Needs
Is such a broad selection of probes really Standard BNC Probes. Probes with a plain BNC connector will connect with virtually all Tektronix oscilloscopes. Low cost passive probes generally have a plain BNC necessary? The answer is Yes, and in this connector.
Page 15 This is only possible, though, when the oscilloscope’s nominal input capacitance is within the compensation range of the probe. Thus, it’s not unusual to find probes with different compensation ranges to meet the requirements of different oscilloscope inputs. www.tektronix.com/accessories...
Page 16: Different Probe Types And Their Benefits
Passive voltage probes are available with various attenuation factors – 1X, 10X, and 100X – for different voltage ranges. Of these, the 10X passive voltage probe is the most commonly used probe, and is the type of probe typically supplied as a standard accessory with oscilloscopes. www.tektronix.com/accessories...
Page 17 And it can a higher voltage. They can even be damage by a static be in situations where the signals are low frequency and have discharge. enough amplitude to be above any concerns of noise. www.tektronix.com/accessories...
Page 18 Options for 25-foot cables are also available for performance is becoming increasingly necessary as disk drive those cases where oscilloscope operation needs to be further read/write data rates reach and surpass the 100 MHz mark. removed from the high-voltage source. www.tektronix.com/accessories...
Page 19 GHz are possible. However, bandwidths under 100 MHz Depending on the probe design, a current probe amplifier may are more typical. also be required for combining and scaling the AC and DC levels to provide a single output waveform for viewing on an oscilloscope. www.tektronix.com/accessories...
Page 20 Figure 2.8 also illustrates a particular class of probe referred current input and voltage output. The result is that waveform to as a split core probe. The windings of this type of probe are peaks are essentially “clipped off” in areas where the amp- second product is exceeded. www.tektronix.com/accessories...
Page 21 These probes offer outstanding electrical characteristics with minimal capacitive loading. www.tektronix.com/accessories...
Page 22: Floating Measurements
EMI environment. Temperature probes, which are used to measure the temperature of components and other heat generating items. Probing stations and articulated arms (Figure 2.10) for probing fine-pitch devices such as multi-chip-modules, hybrid circuits, and ICs. www.tektronix.com/accessories...
Page 23: Danger
CMRR. Additionally, maximum working voltage measurement can be made in far greater safety because the is a key specification for isolation systems. Typically, this is oscilloscope is no longer floating above ground. 600 V RMS or 850 V (DC+peak AC). www.tektronix.com/accessories...
Page 24: Probe Accessories
Switching adaptors between probe models or probe manufacturers is not recommended since it can result in poor connection to the test point or damage to either the probe or probe adaptor. www.tektronix.com/accessories...
Page 25 ABCs of Probes Figure 2.16. An example of the various accessories that are available for a 5-mm (miniature) probe system. Other probe families will have differing accessories depending on the intended application for that family of probes. www.tektronix.com/accessories...
Page 26: A Guide To Probe Selection
Taking full advantage of the oscilloscope’s measurement capabilities requires a probe that matches the oscilloscope’s design considerations. www.tektronix.com/accessories...
Page 27: Understanding The Signal Source
This can be done by setting a logic probe Current Signals to provide a trigger signal to the oscilloscope when a specified Logic Signals logic combination occurs. Other Signals This allows specific logic events to be viewed on the oscilloscope display. www.tektronix.com/accessories...
Page 28 3-dB bandwidth point. However, since the higher harmonics are still present at least to some degree, they’re still able to contribute somewhat to the waveform’s structure. www.tektronix.com/accessories...
Page 29: Understanding The Oscilloscope
R and C presented by the various circuit adjustments? For the former situation, a needle- probe’s output as follows: style probe tip is appropriate, while the latter situation requires = Optimum Signal Transfer some kind of retractable hook tip. scope scope probe probe www.tektronix.com/accessories...
Page 30 Not only does this provide adequate range for your 150-volt signals, it gives you a top-end oscilloscope display range of 1000 volts. However, before connecting any probe to a signal make sure that the signal doesn’t exceed the probe’s maximum voltage capabilities. www.tektronix.com/accessories...
Page 31: Selecting The Right Probe
Test point geometries (leaded component, surface mount, etc.) By considering the above issues and filling in the blanks with information specific to your applications, you’ll be able to specify the oscilloscope and various compatible probes that will meet all of your application needs. www.tektronix.com/accessories...
Page 32: How Probes Affect Your Measurements
For example, with low source impedances, the loading effect of a typical high- impedance 10X probe would be hardly noticeable. This is because a high impedance added in parallel with a low impedance produces no significant change in total impedance. www.tektronix.com/accessories...
Page 33: Capacitive Loading
31 pF. 2.2RC value is the fastest rise time that the pulse can have. This increases the value of 2.2RC and results in an increase in the measured rise time to 3.4 ns versus the 2.2 ns previous to probing. www.tektronix.com/accessories...
Page 34 = 1/2πfC where: = capacitive reactance f = frequency C = probe tip capacitance www.tektronix.com/accessories...
Page 35: Bandwidth Considerations
30% error in amplitude measurements for waveform that you’ll be measuring. frequencies at the bandwidth limit. Usually you won’t be using an oscilloscope at its full www.tektronix.com/accessories...
Page 36 – be sure to use the 2 ≈ Tr 2 + Tr system probe scope manufacturer’s recommended probes. For passive probes, the relationship is more complex, and the above formula should not be used. www.tektronix.com/accessories...
Page 37 Consequently it should not be relied on as a clean, tip. For example, a Tektronix 100 MHz probe provides 100 low-inductive ground return. MHz performance (–3 dB) at the probe tip when used with a compatible 100 MHz oscilloscope. ...
Page 38 This is far more convenient in that it allows you to quickly move the probe from point to point in the circuit under test. Also, the short ground lead that most probe manufacturers supply with their probes provides an adequate ground return path for most measurement situations. www.tektronix.com/accessories...
Page 39 6.5-inch probe ground clip, and it was attached From the examples in Figure 4.13, it’s clear that grounding to a common near the test point. practices have tremendous impact on measurement quality. Specifically, probe ground leads need to be kept as short and direct as possible. www.tektronix.com/accessories...
Page 40: What To Do About Probing Effects
The trade- off is that active probes typically have a low dynamic range. However, if your measurements fit within the range of an active probe, this can be the best choice in many cases. www.tektronix.com/accessories...
Page 41: Understanding Probe Specifications
This specification might also include a time window for the 10X within 3% (for oscilloscope input of 1 MΩ ±2%) aberrations. An example of this would be: Aberrations should not exceed ±3% or 5% peak-to-peak within the first 30 nanoseconds. www.tektronix.com/accessories...
Page 42: Amp-Second Product (Current Probes)
100 MHz. To avoid the uncertainty of overall system needed to be multiplied by 10. The readout systems on bandwidth performance, Tektronix specifies its passive voltage today’s oscilloscopes automatically sense probe attenuation probes to provide a specified measurement system bandwidth factors and adjust the scale factor readouts accordingly.
Page 43: Capacitance (Universal)
A low tip capacitance minimizes errors CMRR at a lower frequency. in making rise time measurements. Also, if a pulse’s duration is less than five times the probe’s RC time constant, the amplitude of the pulse is affected. www.tektronix.com/accessories...
Page 44: Decay Time Constant (Current Probes)
(the primary) that’s being measured. connector. Typically, a current probe’s reflected impedance values are in the range of milliOhms and present an insignificant effect on circuits of 25Ω or more impedance. www.tektronix.com/accessories...
Page 45: Rise Time (Universal)
(1 or 0) is made. The threshold value is set by the user, Tangential Noise (active probes) ranging from TTL levels to, CMOS, ECL, and user-definable. Tangential noise is a method of specifying probe-generated noise in active probes. Tangential noise figures are approximately two times the RMS noise. www.tektronix.com/accessories...
Page 46: Advanced Probing Techniques
This ringing signal is injected in series with the step waveform, how to address the problem. and it’s seen as aberrations impressed on top of the step, as shown in Figure 6.1. www.tektronix.com/accessories...
Page 47 It’s also just as important to realize that aberrations environment and avoid misadjustment of product circuitry seen on a waveform might just be part of the waveform and during installation or maintenance. not a result of the probe grounding method. To distinguish www.tektronix.com/accessories...
Page 48 Additionally, the mechanisms are are discussed as follows. probes and their cables should be kept away from sources of potential interference. In particular, don’t allow probe cables to lie alongside or across equipment power cables. www.tektronix.com/accessories...
Page 49: Caution
If the probe ground lead is positioned too close to certain areas on the circuit board under test, such as clock lines, the ground lead may pick up signals that will be mixed with the signal at the probe tip. www.tektronix.com/accessories...
Page 50: Differential Measurements
V signal (a few volt swing) at sufficient resolution, such as 2 V/division, while rejecting the = the amplifier’s gain several-hundred-volt transition of the source to ground. = the output signal referenced to earth ground www.tektronix.com/accessories...
Page 51 V at the output of the differential amplifier, which would be 80 V/10,000 or 8 mV. The 8 mV of residual commonmode signal represents up to a 22% error in the true 35 mV signal! www.tektronix.com/accessories...
Page 52 When attenuation is needed for high-voltage or high-frequency applications, special passive probes designed specifically for differential applications should be used. www.tektronix.com/accessories...
Page 53: Small Signal Measurements
Thus, averaging just two waveform acquisitions (2 ) provides noise and adequate measurement sensitivity. up to 3 dB of SNR improvement, averaging four acquisitions ) provides 6 dB of improvement, eight averages (2 provides 9 dB of improvement, and so on. www.tektronix.com/accessories...
Page 54 If any of these appear to be a problem, then a better approach is to take advantage of the much higher bandwidths and lower loading typical of 1X active probes. www.tektronix.com/accessories...
Page 55: Explanation Of Safety Precautions
Except for the probe tip and the probe connector center conductor, all accessible metal on the probe (including the ground clip) is connected to the connector shell. www.tektronix.com/accessories...
Page 56: Avoid Exposed Circuitry
Also, some fine dusts or powders suspended in the air may present an explosive atmosphere. www.tektronix.com/accessories...
Page 57: Glossary
This return path is capacitance – An electrical phenomenon whereby an electric provided by a probe ground lead that is attached to the circuit charge is stored. ground or common. www.tektronix.com/accessories...
Page 58 “no load” situation. some form of active electronics and, thus, are referred to as being active probes. loading – The process whereby a load applied to a source draws current from the source. www.tektronix.com/accessories...
Page 59 (T ) – On the rising transition of a pulse, rise time is the time it takes the pulse to rise from the 10% amplitude level to the 90% amplitude level. www.tektronix.com/accessories...
Page 60 TEK.COM Copyright © Tektronix. All rights reserved. Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supersedes that in all previously published material. Specification and price change privileges reserved. TEKTRONIX and TEK are registered trademarks of Tektronix, Inc. All other trade names referenced are the service marks, trademarks or registered trademarks of their respective companies.

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