How to accurately detect power quality and circuit anomalies using the advanced triggering function of a digital oscilloscope?
Taking GW Instek GDS-2000HG and ASR-6000 as examples
Keywords: Power Quality Anomalies, Advanced Triggering, Digital Oscilloscope.
Abstract: In the fields of information systems (IT) and semiconductor equipment development, whether equipment can meet industry power quality standards (such as the ITI (CBEMA) Curve, which specifies the voltage tolerance of servers and information equipment, and the SEMI 47 specification, which specifies semiconductor equipment) is crucial to determining equipment reliability.
In the power grid, anomalies such as voltage spikes, drops, and interruptions require engineers to rely on digital oscilloscopes for precise measurements and compliance verification. However, capturing fleeting abnormal waveforms within thousands of normal cycles requires more than simple edge triggering.
A comprehensive understanding of digital oscilloscope triggering capabilities is essential to dealing with these unpredictable anomalies. This article explores three advanced applications of digital oscilloscope triggering, simulating power quality anomalies using the GW Instek ASR-6000 series AC/DC power supplies.
It also provides a practical analysis of how to accurately pinpoint problems using the window, runt, and timeout triggering functions of the GDS-2000HG 12-bit digital oscilloscope. Furthermore, it shares classic applications of these triggering techniques in digital logic circuits.
Why are "advanced triggering features" so important for debugging in engineering?
Edge triggering is the most familiar and commonly used triggering function for engineers. However, when faced with complex AC voltage variations or erroneous logic signals embedded in normal packets, simple edge triggering often triggers repeatedly on normal waveforms, causing the true abnormal waveform to flash by or be difficult to locate.
Some engineers repeatedly press the run/stop trigger button, trying to capture these anomalies by chance. To effectively complete this type of measurement task, we must make good use of the advanced triggering functions of digital oscilloscopes.
By setting specific voltage conditions and time limits, the oscilloscope can act like a filter, freezing the waveform on the screen only when a true anomaly occurs. This not only significantly reduces debugging time but also helps engineers more accurately verify whether the design margin of the equipment meets expectations.
In this test architecture, we will use the following two GW Instek instruments:
- ASR-6000 Series AC/DC Power Supplies
Features powerful built-in waveform editing and sequence functions, enabling accurate simulation of various power grid anomalies. For application details of the ASR series, please refer to the AC/DC Power Supply Application White Paper. - GDS-2000HG series oscilloscopes
Featuring 12-bit vertical resolution, capable of clearly displaying minute voltage changes, and with a wealth of advanced triggering options built-in.
Below, we will break down the setup secrets and comprehensive applications of the three advanced trigger modes step by step.
Practical Example 1: Window Trigger
Phenomenon Description and Simulation:
Voltage surge refers to a sudden increase in AC voltage on the power grid due to the unloading of nearby electrical equipment, which may damage the overvoltage protection components in the power supply circuit.
The setup for this case is as follows:
Using the ASR-6000, we increased the normal AC voltage of 110 Vrms / 50 Hz to 140 Vrms in the second step and maintained it for 3 cycles (see the setup screenshot in Figure 1).
Figure 1: Steps for generating a voltage surge using ASR-6000
GDS-2000HG Trigger Setting:
• Principle:
Window triggering allows setting an "upper voltage limit" and a "lower voltage limit," forming a monitoring window. The oscilloscope will trigger immediately whenever the waveform "exits" this window (up or down).
• Setting Steps:
Select Window triggering and observe a normal 110 Vrms (peak value approximately ±155V). Set the upper limit of the window to +165 V, the lower limit to -165 V, and the trigger condition to "Outside."
• Result:
The normal waveform will remain in the window. When the ASR-6000 outputs a 140 Vrms surge waveform, the voltage exceeds the +165V upper limit, and the GDS-2000HG is triggered instantly, perfectly capturing the complete transient process.
Figure 2: Waveform of voltage surge captured by GDS-2000HG application window trigger
Besides AC voltage, window triggering is also very suitable for monitoring signals that "should remain stable but exhibit abnormal spikes":
• Server core components have extremely small tolerance for DC power supply variations. Set the upper and lower limits of the window trigger within the allowable tolerance of the 3.3 V DC voltage (e.g., ±5 %). Once load switching causes the voltage to go beyond the window, the digital oscilloscope can immediately capture the event.
• Digital signal overshoot: Overshoot caused by the oscillation of the inductor-capacitor (LC) circuitry in high-speed digital signals. A normal operating voltage window is set; as long as an overshoot occurs and the signal passes through the window, precise triggering is achieved.
Practical Application 2: Runt Trigger
Core Application: Capturing Voltage Dips /Sag
Phenomenon Description and Simulation:
Voltage dips are a common power quality issue in industrial environments, referring to a sudden drop in AC voltage caused by the startup of nearby large electrical equipment. Using the ASR-6000, a 110 Vrms signal is generated, and a voltage drop to 80 V is inserted for three consecutive cycles.
Figure 3: Steps for generating a voltage sag using ASR-6000
GDS-2000HG Trigger Setting:
• Principle:
A Runt trigger can be configured with two trigger thresholds and is specifically used to capture waveforms that are above the lower trigger threshold and below the upper trigger threshold.
• Setting Steps:
Select Runt triggering. For a normal 110 Vrms waveform (peak value approximately 155 V), set the low threshold to +20 V and the high threshold to +131 V, with positive polarity.
• Result:
A normal waveform will cross both thresholds without triggering. When a sudden drop occurs, the peak value is only about 80 V. The waveform crosses +20 V but doesn't reach +131 V before dropping. The GDS-2000HG detects this "runt" and locks the display.
Figure 4: Waveform of GDS-2000HG capturing voltage dips using runt triggering
Runt triggers are particularly useful for catching signals with insufficient amplitude, a common problem in digital logic circuits and clock signal debugging:
• Logic Level Error
Bus contention or insufficient drive during I2C or SPI communication can produce a "runt" waveform that fails to reach the standard high level, leading to decoding failure. Setting a double threshold of logic 0 and 1 can easily detect error signals hidden in normal packets.
• Poor Clock Start-up:
The quartz oscillator's amplitude is unstable when it first starts up. Using Runt triggering can capture the weak pulses during the clock signal's rise, before it reaches the operating voltage standard.
Practical Application 3: Timeout Trigger
Core Application: Capturing "Voltage Interruption"
Phenomenon Description and Simulation:
A voltage interruption refers to the complete loss of power supply for several milliseconds to several seconds, testing the power supply's hold-up time. Using the ASR-6000, we simulated a 20 ms complete power outage (0 V) while supplying 110 Vrms power followed by a restart.
Figure 5: Steps for generating a voltage interruption using ASR-6000
GDS-2000HG Trigger Setting:
• Principle:
Timeout trigger monitors the signal status. If the waveform remains at the trigger level on the rising or falling edge for a time exceeding the set limit, the oscilloscope will force trigger.
• Setting Steps:
Select Timeout trigger. The period of 50 Hz AC is 20 ms. Set the trigger level to 70 V, and the timeout condition to the signal remaining at the falling edge of 70 V for more than 20 ms.
• Result:
Under normal power supply, the time below 70 V is always less than 20 ms; during the momentary interruption, the voltage returns to zero, and the time count reaches 20 ms (below 70 V exceeds one normal cycle of 20 ms). The GDS-2000HG determines "timeout abnormality" and triggers immediately, clearly showing the momentary interruption voltage waveform at the instant and the restart. A common example in life is a light flashing (power is supplied after a momentary interruption).
Figure 6: Waveform of GDS-2000HG application capturing voltage momentary interruption using timeout trigger.
The core of timeout triggering lies in the "stagnation of time and state," making it the best tool for monitoring digital communication protocols.
• Bus Lockup and Packet Interval: If an I2C signal line is pulled low for an extended period due to a software lockup, setting a timeout (e.g., maintaining a low level for more than 50 ms) can immediately detect the crash. It is also commonly used to trigger the "end" of data packets, as the idle time between packets is usually longer than the bit interval.
• Watchdog Timer Failure Detection: The microcontroller (MCU) needs to periodically send pulses to the watchdog timer to confirm that the circuit is in normal working condition, commonly known as "feeding the dog". Set the timeout period to be slightly longer than the feeding period. If the MCU crashes and fails to send pulses, the oscilloscope will trigger due to "timeout", helping to clarify the crash state.
Conclusion: Easily Overcome Regulatory Barriers with the Right Triggering Tools
In modern electronic product and industrial equipment design, verifying the stability of equipment under various power quality conditions is an indispensable step.
The tests above clearly demonstrate that the GW Instek ASR-6000 series can easily reproduce various harsh power anomalies; while the GDS-2000HG transforms the previously arduous task of capturing abnormal waveforms into a simple, reliable, and standardized testing process, boasting a vertical accuracy of ±1.5 % and a horizontal accuracy of ±1 ppm, making it a leader in its field.
Stop wasting time letting your digital oscilloscope continuously trigger on valid waveforms! Mastering these three advanced triggering settings will allow you to achieve twice the results with half the effort, significantly accelerating your product launch timeline, whether facing poor power quality or unpredictable digital signal errors.
(For more detailed specifications and applications of the GDS-2000HG series 12-bit high-resolution digital oscilloscopes and ASR-6000 series AC power supplies, please visit the GW Instek official website.)
GDS-2000HD/HG Series
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ASR-6000 Series
High Performance AC/DC Power Source
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Diana
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