While you can make a wide variety of measurements with an ordinary ground-referenced scope, there are some circumstances where that just won't work. 
Common-mode voltages are unwanted signals that are applied equally to both measurement terminals in your probing system. The circuit above consists of a signal source (purple) with AC and DC components producing a total output of VSIG, which we wish to measure. However, the circuit also contains an unwanted voltage source (green) that also has AC and DC components adding up to VCM, a common-mode voltage. This situation is quite common, for example when probing high-side drivers in amplifiers and power supplies. As the diagram above shows, probing this circuit with a single-ended scope results in a distorted waveform (VSUM) on the display. We cannot simply connect the probe ground to the negative terminal of VSIG, as that would short-circuit VCM to ground through the oscilloscope, possibly causing a circuit malfunction or damage to the instrument. We need a measuring system that can safely detect VSIG and ignore VCM. The solution, as shown below, is to connect a differential scope input across the positive and negative terminals of the signal source. The differential input does not measure VCM, only VSIG, so VSIG is what you see on the oscilloscope display. 
Differential scopes can measure the AC or DC voltage between two points connected to the positive and negative leads, when neither of the points is grounded. This enables them to take measurements where single-ended scopes can't, for example at voltages that are much higher than ground potential. The resulting measurements focus exclusively on the potential difference between the probes.
| Vertical |
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| OSCILLOSCOPE SPECIFICATIONS | SPECIFICATIONS WITH PICOCONNECT 442 1kV CAT III PROBE | | Input channels | 4 channels | 4 channels | | Analog bandwidth (-3 dB) | 20MHz with D9-BNC adaptors
15MHz with PicoConnect 441 probe | 10MHz | | Rise time (calculated) | 17.5ns with D9-BNC adaptors
23.3ns with PicoConnect 441 probe | 35ns | | Bandwidth limiter | 100kHz or 1MHz (selectable) | 100kHz or 1MHz (selectable) | | Vertical resolution, 12-bit mode | 12 bits on most input ranges
11 bits on ±10mV range | 12 bits | | Vertical resolution, 14-bit mode | 14 bits on most input ranges
13 bits on ±20mV range
12 bits on ±10 mV range | 14 bits | Enhanced vertical resolution
(PicoScope 6 software), 12-bit mode | Up to 16 bits on most input ranges
Up to 15 bits on ±10 mV range | 16 bits | Enhanced vertical resolution
(PicoScope 6 software), 14-bit mode | Up to 18 bits on most input ranges
Up to 17 bits on ±20mV range
Up to 16 bits on ±10mV range | 18 bits | | Input type | Differential
9-pin D-subminiature, female | Differential
9-pin D-subminiature, female | | Input characteristics | 1 MΩ ±1%, in parallel with 17.5pF ±1pF
(each differential input to scope ground).
<1pF difference between ranges. | 16.7MΩ ±1%, in parallel with 9.3pF ±1pF
(each differential input to scope ground) | | Input coupling | AC or DC | AC or DC | | Input sensitivity | 2mV/div to 10V/div | ±0.5V/div to ±200V/div | | Input ranges (full scale) | ±10mV, ±20mV, ±50mV, ±100mV, ±200mV, ±500mV,
±1V, ±2V, ±5V, ±10V, ±20V, ±50V | ±2.5V, ±5V, ±12.5V, ±25V, ±50V, ±125V, ±250V, ±500V, ±1000V | | Input common mode range | 5V on ±10mV to ±500mV ranges
50V on ±1V to ±50V ranges | 125V on ±2.5V to ±12.5V ranges
1000V on ±25V to ±1000V ranges | | DC accuracy (DC to 10 kHz) | ±1% of full scale, ±500µV | ±3% of full scale, ±12.5mV | | Analog offset range | ±250mV on ±10mV to ±500mV ranges
±2.5V on ±1V to ±5V ranges
±25V on ±10V to ±50V ranges | ±6.25V on ±2.5V to ±12.5V ranges
±62.5V on ±25V to ±125V ranges
±625V on ±250V to ±1000V ranges | | Analog offset accuracy | 1% of offset setting in addition to basic DC accuracy | 1% of offset setting in addition to basic DC accuracy | | Overvoltage protection | ±100V DC + AC peak (any differential input to ground)
±100 DC + AC peak (between differential inputs) | CAT III 1000V |
| Horizontal |
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| Maximum sampling rate (real time)12-bit mode | 1 channel: 400MS/s
2 channels: 200MS/s
3 or 4 channels: 100MS/s | Maximum sampling rate (real time)
14-bit mode | 50MS/s | | Maximum sampling rate (USB streaming) | 16.67 MS/s | | Shortest real-time collection time, 12-bit mode | 50 ns (5 ns/div) | | Shortest real-time collection time, 14-bit mode | 200 ns (20 ns/div) | | Longest real-time collection time | 50000 s (5000 s/div) | | Capture memory (block mode) | 256 MS shared between active channels | | Capture memory (USB streaming mode) | 100 MS (shared between active channels) | | Waveform buffers | 10000 | | Collection time accuracy | ±50ppm (5ppm/year aging) | | Sample jitter | 3ps RMS typical | | ADC sampling | Simultaneous sampling on all enabled channels |
| Dynamic Performance (Typical) |
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| OSCILLOSCOPE SPECIFICATIONS | SPECIFICATIONS WITH PICOCONNECT 442 1kV CAT III PROBE | | Crosstalk | 2000:1 DC to 20MHz | 2000:1 DC to 10MHz | | Harmonic distortion at 100kHz, 90% of full scale | < -70dB on ±50mV ranges and higher
< -60dB on ±10mV and ±20mV ranges | < -70dB | | SFDR | > 70dB | > 70dB | | ADC ENOB, 12-bit mode | 10.8 bits | 10.8 bits | | ADC ENOB, 14-bit mode | 11.8 bits | 11.8 bits | | Noise | < 180µV RMS on ±10mV range | < 5mV RMS on ±2.5V range | | Bandwidth flatness | (+0.1dB, -3 dB) DC to full bandwidth | (+0.1dB, -3 dB) DC to full bandwidth | | Common mode rejection ratio | 60dB typical, DC to 1MHz | 55dB typical, DC to 1MHz |
| Triggering |
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| Source | Any input channel | | Trigger modes | None, auto, repeat, single, rapid | | Trigger types | Edge, window, pulse width, window pulse width, dropout, window dropout, interval, runt pulse, logic | | Trigger sensitivity | Digital triggering provides up to 1 LSB accuracy up to full bandwidth | | Maximum pre-trigger capture | Up to 100% of capture size | | Maximum trigger time-delay | 4 billion samples | | Trigger rearm time | < 2µs on fastest timebase | | Maximum trigger rate | 10 000 waveforms in a 12ms burst |
| Probe Compensation Pins |
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| Output level | 4V peak | | Output impedance | 610Ω | | Output waveforms | Square wave | | Output frequency | 1kHz | | Overvoltage protection | ±10V |
| Spectrum analyzer |
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| Frequency range | DC to analog bandwidth of oscilloscope | | Display modes | Magnitude, average, peak hold | | Windowing functions | Rectangular, Gaussian, triangular, Blackman, Blackman-Harris, Hamming, Hann, flat-top | | Number of FFT points | Selectable from 128 to half available buffer memory in powers of 2, up to a maximum of 1 048 576 points |
| Math Channels |
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| General functions | −x, x+y, x−y, x*y, x/y, x^y, sqrt, exp, ln, log, abs, norm, sign, sin, cos, tan, arcsin, arccos, arctan, sinh, cosh, tanh, derivative, integral, delay | | Filter functions | Lowpass, highpass, bandstop, bandpass | | Graphing functions | Frequency, duty cycle | | Multi-waveform functions | Min, max, average, peak | | Operands | Input channels, reference waveforms, time, constants, pi |
| Automatic Measurements |
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| Scope mode | AC RMS, true RMS, frequency, cycle time, duty cycle, DC average, edge count, falling edge count, rising edge count, falling rate, rising rate, low pulse width, high pulse width, fall time, rise time, minimum, maximum, peak to peak | | Spectrum mode | Frequency at peak, amplitude at peak, average amplitude at peak, total power, THD %, THD dB, THD+N, SFDR, SINAD, SNR, IMD | | Statistics | Minimum, maximum, average and standard deviation |
| Serial Decoding |
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| Protocols | 1-Wire, ARINC 429, CAN, CAN FD, DCC, DMX512, Ethernet 10Base-T, FlexRay, I²C, I²S, LIN, PS/2, SENT, SPI, UART (RS-232 / RS-422 / RS-485), USB 1.0/1.1 |
| Mask Limit Testing |
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| Mask generation | Numeric (automatic) or graphical (manual) | | Statistics | Pass/fail, failure count, total count | | Available actions on mask fail | Beep, play sound, stop capture, save waveform, trigger signal generator / AWG, run executable |
| Display |
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| Interpolation | Linear or sin(x)/x | | Persistence modes | Digital color, analog intensity, custom, fast or none |
| SDK/API Details & Specifications for Users Writing their own Software (see “Horizontal” above for details when using PicoScope 6 software) |
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| Supplied drivers | 32 and 64-bit drivers for Windows 7, 8 and 10
Linux drivers
Mac OS X drivers | | Example code | C, C#, Excel VBA, VB.NET, LabVIEW, MATLAB | | Maximum sampling rate (USB streaming) | 50MS/s | | Capture memory (USB streaming) | Up to available PC memory | | Segmented memory buffers | > 1 million |
| Software |
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| Windows software | PicoScope for Windows Software development kit (SDK) Windows 7, 8 or 10 recommended | | macOS software | PicoScope for macOS Software development kit (SDK) OS versions: see release notes | | Linux software | PicoScope for Linux Software development kit (SDK) See Linux Software & Drivers for details of supported distributions | | Languages | Chinese (simplified), Chinese (traditional), Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hungarian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish |
| General Specifications |
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| PC connectivity | USB 3.0, compatible with USB 2.0, USB 1.1 | | Power requirements | USB port or external DC PSU, depending on connected accessories | | Dimensions | 190 x 170 x 40mm including connectors | | Weight | < 0.5kg | | Temperature range, operating | 0°C to 45°C | | Temperature range, operating, for quoted accuracy | 15°C to 30°C | | Temperature range, storage | -20°C to 60°C | | Humidity range, operating | 5% to 80% RH non-condensing | | Humidity range, storage | 5% to 95% RH non-condensing | | Altitude | Up to 2000 m | | Pollution degree | Pollution degree 2 | | Safety approvals | Designed to EN 61010-1:2010 | | EMC approvals | Tested to EN 61326-1:2013 and FCC Part 15 Subpart B | | Environmental approvals | RoHS and WEEE compliant | | PC requirements | Processor, memory and disk space: as required by the operating system Port(s): USB 3.0 or USB 2.0 |
- General-purpose passive differential probe
- Measuring voltages on ranges from ±10 mV to ±50 V
- Used with the PicoScope 4444 only
PicoConnect 441 differential 1:1 probe - 1000 V CAT III, passive differential probe
- 25:1 10 MHz voltage measurement
- Used with the PicoScope 4444 only
PicoConnect 442 1000 V CAT III 25:1 differential probe - 40 A AC/DC, 300 V CAT III
- 100 kHz current measurement
- Used with the PicoScope 4444 only
TA300 current probe 40 A AC/DC D9 connector - 200/2000 A AC/DC, 150 V CAT II
- 20 kHz current measurement probe
- Used with the PicoScope 4444 only
TA301 current probe 200/2000 A AC/DC D9 connector - Flexible 3-phase switched-range 30/300/3000 A AC RMS
- 1000 V CAT III, 10 Hz to 20 kHz current probe
- Used with the PicoScope 4444 only
- 3 x TA271 D9-BNC Adaptors required
TA325 Flex current probe 3-phase 30/300/3000 A AC BNC - Flexible single-phase switched-range 30/300/3000 A AC RMS
- 1000 V CAT III, 10 Hz to 20 kHz current probe
- Used with the PicoScope 4444 only
TA326 Flex current probe 30/300/3000 A AC BNC - Suitable for ground-referenced measurements
- Essential when using the TA325 and TA326 current probes
- Used with the PicoScope 4444 only
- Suitable for differential measurements using two single-ended probes
- Used with the PicoScope 4444 only
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