When we use power amplifiers to amplify signals or when we need to detect signals, we may use a testing and measuring device called a high-voltage probe and a high-voltage differential probe. Do you know the difference between a high-voltage probe and a high-voltage differential probe?

1、 High voltage probe andDifferential probeBasic concepts

1. High voltage probe: a "step-down converter" for single ended high voltage signals

The design goal of high-voltage probes is to measure high amplitude single ended signals, that is, the scenario where one end of the signal is the measured point and the other end is ground (GND). The core principle is to attenuate high voltage signals of thousands or even tens of thousands of volts into low voltage signals that the oscilloscope can withstand at a fixed ratio (such as 100:1, 1000:1) through a precise voltage divider network (usually composed of high voltage resistors and capacitors to achieve "resistance capacitance voltage division" to ensure wideband characteristics), usually not exceeding the input range of the oscilloscope, such as 5V, 10V; (Similar to attenuator mode).

For example, a 1000:1 high voltageProbe stickThe measured signal of 10kV can be attenuated to 10V and transmitted to an oscilloscope, which then calculates the amplitude of the original signal in reverse through the "probe attenuation ratio setting". Its essence is "single ended ground measurement", which must rely on the common ground as a reference point, measuring the "potential difference of the signal relative to ground".

2. Differential probe: a "common mode suppressor" for floating signals

The design goal of differential probes is to measure the potential difference (differential signal) between two non grounded nodes, especially suitable for scenarios with "no common ground" or "unstable ground potential" (i.e. "floating measurement"). The core principle is to collect the signals of two measured points (called "+terminal" and "- terminal") through two symmetrical signal conditioning channels, and then subtract the two signals through an internal operational amplifier to finally output a differential signal of "+terminal potential - terminal potential".

More importantly, the common mode rejection ratio of differential probes（CMRR）- Can effectively suppress common interference signals that exist simultaneously at the+and - ends（Common mode signal）”Extract only useful differential signals. For example, when measuring the voltage between the upper and lower bridge arms in a motor drive circuit, both signals may carry 100VCommon mode interferenceHowever, the differential probe can filter out this interference and accurately measure the true potential difference of 5V between the two. Its essence is "dual ended non ground measurement", which does not rely on a common ground and measures the "relative potential difference between two points"

2、 The difference between high-voltage probes and differential probes

1. Different functions

high pressureProbe stickMainly used for measuring high voltage signals, such as voltage signals from high-voltage power sources, relays, switches, and other equipment in power systems. Differential probes are used to measure the potential difference between two points in signal transmission, such as signal interference, noise, common mode signals, etc.

2. Different measurement ranges

high pressureProbe stickUsually used for measuring and maintaining DC or AC high-voltage power supplies, with a measurement range typically ranging from several hundred volts to several thousand volts. Differential probes are commonly used in signal measurement, with a measurement range typically ranging from tens of millivolts to hundreds of volts.

3. Different accuracies

high pressureProbe stickThe measurement accuracy is relatively low, usually around 1% to 2%. Differential probes have higher measurement accuracy, typically reaching 0.1% to 0.2%.

3、 Advantages and disadvantages of high-voltage probes and differential probes

high pressureProbe stickThe advantage is that it has a wide range of applications, high safety and reliability. The disadvantage is that the measurement accuracy is low and it is not suitable for situations that require high signal accuracy.

The advantage of differential probes is high measurement accuracy and high application value in signal analysis. The disadvantage is that it is expensive and not suitable for general measurement work

high pressureProbe stickDifferential probes are important measurement tools in the field of sensors, each suitable for different testing scenarios. Suitable probes should be selected according to actual needs during use.

4、 Misconceptions and Precautions in Selection

In practical applications, measurement errors or equipment damage caused by confusion between the two functions are extremely common, and the following misconceptions should be avoided:

1. Misconception 1: Measuring Differential Signals with High Voltage Probes

If high voltage is appliedProbe stickThe "ground" is connected to a floating node, and the "measuring end" is connected to another floating node. It seems to be able to measure the pressure difference between the two, but the high voltageProbe stickWithout common mode rejection capability, common mode interference (such as ground potential difference) on two nodes will be directly included in the measurement results, resulting in severe data distortion; Even more dangerous is that if the common mode voltage of two nodes exceedsProbe stickThe isolation voltage may cause breakdownProbe stickInternal insulation, burning the oscilloscope.

2. Misconception 2: Measuring ultra-high voltage single ended signals with differential probes

The "differential voltage range" of differential probes is usually much lower than that of high-voltage probes (such as differential probes with a maximum differential voltage of only 1000V, while high-voltage probes can reach 10kV). If used to measure ultra-high voltage single ended signals (such as 5kV to ground voltage), it is equivalent to grounding the "+" and "-" terminals of the differential probe with 5kV. The differential voltage (5kV) far exceeds the limit that the probe can withstand, which will directly damage the operational amplifier or isolation circuit inside the probe.

3. Precautions: Isolation and safety

high pressureProbe stickConfirm the isolation voltage between the probe front end and the oscilloscope ground to avoid electric shock or equipment damage caused by the measured voltage exceeding the isolation value;

Differential probes need to confirm the "common mode voltage range" to ensure that the ground voltage (common mode voltage) of the two tested nodes does not exceed the common mode withstand limit of the probe;

Regardless of the type of probe used, it is necessary to follow the operating procedure of "connect the probe first, then connect the measured signal; disconnect the measured signal first, then remove the probe" to avoid equipment damage caused by transient surges